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HOW IT's DONE - IMPLEMENTATION

Best configurations 

Planets -

                 C6 SCT/Svbony                            1.1 asecs   0.3 asecs/pix  3 amin field, sharpened resolves 0.5 asec space

                 Nikon P1000                                  2 asecs  almost see 0.5 asecs gap in Saturn's rings. 

                 480R/5x/Svbony                            2 asec       0.13 asecs/pix,

Milky Way  14/20mm Sony a7s                     1 amin    30 sec exposure w/o scanning stage

Nebula -  100mm Sony a7s                           20 asec    5 sec exposure w/o scanning stage

Nebula  - 480R/FF/Sony a7s                          3 asec   line  pixel limited, best for difficult mobile applications. 

Nebula details  C6 SCT/QHY(RGB)               0.8 asec    

Galaxies -  480R/FF/QHY(RGB)                      3 asec    

Dim Galaxies C6 RASA/QHY(RGB)                4 asec

HSO      - C6 RASA/QHY                                  4 asec l/s  MTF = 0.5. Demo 4.5 asecs FWHM spot size

System metrics

C6 SCT/QHY f10 has 30 amin field with 0.3 asec/pix for high resolution applications. 

For target finding;  400R/a7s has 3 deg field with 2.6 asec/pix, so 6x larger field to find target 

For tracking; 400R/Svbony has 40 amin field with 1.2 asec/pix, so 1 asec RMS  tracking error feasible. 

C6 SCT/Svbony f10  has 10 amin field with 0.3 asec/pix. For planets, lucky imaging requires <10 msec exposure and reduced download area of 600x600 pixels. Collect 10K images in 60 sec increments. Stack best10% of images with 3x drizzle to produce 0.1 asec/pix. Adjust images +30% saturation for correct color depth. 

C6 RASA/QHY  f2 has 2 degree field with 1.3  asec/pix, so will image the whole of Andromeda.  Hyperstar set with all screws at flange contact. Resolution 4 asecs MTF 0.5, that is aberration limited so no obscuration impact. Usable images of 10 arcmin objects.

Seestar s50 is an interesting "turnkey" system $500. Refractive optic with aperture 50mm translates to a 4.6 asecs resolution at MTF 0.5. Focal length 250mm and small field camera covers around 3 degrees @ 4 asecs/pix. Auto stacking and drizzle produces good looking Whirlpool images. Alts stage limits exposure to 10 secs, but no need for cooling.

Performance

MTF l/s and FWHM of a single spot should be close. HFD as reported by PHD2 tracking app is close to FWHM.

MTF measured in house with 16m distance to target, printed target with 0.1mm lines or 1.3 asec resolution.

C6 SCT > 480R (ED 80) = Nikon P1000 > C6 RASA > 400R (Pentax)

C6 SCT Rayliegh limit is 0.4 asec l/s at MTF 0.1. MTF 0.5 resolution is 1.6 asec l/s, simliar to HFD 1.4 asec.  The lower resolution for high contrast features is caused by  mirror obscuration. Saturn's ring Cassini gap is 0.5 asec so should be clearly visible with sharpening with perfect seeing or lucky imaging. 

 

Comparison Nikon P1000 with C6SCT clearly shows C6SCT with better resolution of fine features, high contrast limited to 1 asec due to obscuration from mirror. Will see difference in planets. 

Location impact

The background light level is classified by Bortle level, and settles the maximum exposure time to achieve an IU value of around 50.  The Bortle level roughly relates to relative brightness. Measured using Sony a7s as the reference detector. 

Brightness =  IU(8bit) * Lens  block  *  Filter block / ISO / exposure time

 Location           Bortle    Bkg 1/ISOsecs  Rel Bkg     B/Noise Sony      B/Noise QHY  cooled

Grand Tetons        1              0.006                  1                    5

Junction                  2-3          0.001-0.0028     3.3                 3

Wimberly                4             0.0033                5.5                2.5                  3.3 (low I)

Austin                      5             0.0036                6.0                                        5 

Line filter reduces intensity 180x, background 1.7x

Camera limitations 

Cameras             Type       Chip        Pixel   Pixel     ADC       Pixel      Diagonal  Tech(1).    Noise(2)  IU         Introduced  Backfocus

                                                           um                  bit        count       mm                         RT        -15C           

Nikon  1000      RGB       IMX206    1.34 4000      12          16M         8            EX-R            120                       2018/2013

Sony 7a             RGB       IMX235    8.4   3600      14          12M         43          EX                5                        2014        18mm

QHY 183 cool   Mono    IMX183    2.4   5339      12          20M         15          EX-R            4         1             2017        17.5mm 

Svbony 305       RGB       IMX290   2.9   1920       12            2M          9           EX-R                                                       11.5mm +9 mm t2 adaptor = 20.5mm

Neximage 10    RGB        ONSemi  1.6   3800      12          11M          6                                                                                           ON Semi MT9J003 

IPhone 14         RGB        IMX703    1.22  8000     10          48M        15           EX-R stacked                       2022/2018  Main 1x camera

Canon E mount                                                                                                                                                                    44mm

Pentax M42                                                                                                                                                                           45mm

Exmor technologies 

https://www.framos.com/en/articles/what-is-sonys-exmor-technology-anyway

(1) EX = Exmor.  EX-R  = Exmor - R.  Exmor R is a back-illuminated version of Sony's CMOS image sensor.[3] Exmor R was announced by Sony on 11 June 2008 with the device fabricated, and then lapped back so that the light is not blocked by the wiring layers. The semiconductor layer is still shared between diode and transistor. Sony has newly developed Exmore RS  a unique photo-diode structure  where the transistor is underneath the diode, increasing the diode area by as much as 2x. The on-chip lens optimized for back-illuminated structures, that achieves a higher sensitivity of +6dB and a lower random noise of -2dB without light by reducing noise, dark current and defect pixels compared to the conventional front-illuminated structure, 8 dB translates to a 3x improvement. 

(2) Noise at around ISO3200 20sec exposure.  G30 on QHY = 3200 ISO.

SVBONY SV305 Pro Telescope Camera, 2MP USB3.0 Astronomy Camera - IMX290 Chip. IMX 533 chip has 3x full well, better S/N. 

Noise data at https://player-one-astronomy.com/product/mars-mono-camera/

IMX235 is in the heart of Sony A7S and A7Sii. It has a large pixel making the fill factor better compared to smaller pixel design at the same technological process. In fact, the 18% SNR curve puts this sensor comparable to the Nikon D850’s back-illuminated CMOS.

https://landingfield.wordpress.com/

July 23, 2018 Tokyo, Japan—Sony Corporation today announced the upcoming release of the IMX586 stacked CMOS image sensor for smartphone cameras. The new sensor features 48 effective megapixels*2, the industry’s highest pixel count.*1 The new product achieved a world-first*3 ultra-compact pixel size of 0.8 μm, making it possible to pack 48 effective megapixels*2 onto a 1/2-type (8.0 mm diagonal) unit, thereby supporting enhanced imaging on smartphone cameras.​  By adopting the Quad Bayer color filter array, where the adjacent 2x2 pixels come in the same color, the new sensor delivers both high sensitivity and high resolution. In low light situations, such as shooting at night, the signal from the four adjacent pixels are added, raising the sensitivity to a level equivalent to that of 1.6 μm pixels (12 effective megapixels), to capture bright, low-noise photos and videos. When shooting bright scenes such as daytime outdoors, the built-in, original signal processing function performs array conversion, making it possible to obtain high-definition 48 effective megapixel images in real time. Phase sensitive focus.

PROGNOSIS - next gen Nikon P1000 in 2023 can use current lens, lens needs larger field size / shorter focal length with much larger pixel count, stabilized video, faster auto focus.  

 https://www.dpreview.com/articles/4613822764/high-iso-compared-sony-a7s-vs-a7r-vs-canon-eos-5d-iii/2

Future developments -

The X27 utilizes newly advanced BSTFA (Broad Spectrum Thin Film Array) Technology. 5M ISO ! used for Netflix Night Life documentary . SPI CORP has FINALLY introduced the X26 HFIS (Hyper Fidelity Intensified Sensor) which meets and exceed the performance of Image intensifiers and is purely Digital, The X26 sees up to 1100 Nm right at  the edge of Si band gap.  Cooled A7 full frame, no IR filter, best guess BSFTFA couples much broader wavelength range  into chip. 

https://www.x20.org/

ISO - Gain

ISO speed ratings of a digital camera are based on the properties of the sensor and the image processing done in the camera.  Decibels of gain for an amplifier is 20 x log10 of the voltage ratio.  For a video camera that would translate to a doubling of the ISO for each 6dbB of gain. 

 

The photo-speed of different cameras can be matched as follows. 

QHY 183C has a full well of 15k electrons. Sony a7s has a pixel area 10x the QHY, so a full well is around 150k electrons. The base ISO is 50, so a table of ISO and full well shows that for ISO 25,600 there are 293 electrons in a full well delivering a 8 bit color depth with 256 levels - 1 electron per level change. At an ISO of 409k, the image has a 4bit depth. At the Milky Way reference exposure conditions of ISO2000, the image has a 11 bit color levels. 

QHY 183C at a gain of 30 -dB matches the exposure time for Sony a7s at ISO800. An 8 bit image is obtained at gain of 36 -dB or ISO1600, the maximum ISO for quality images.  

Nikon P1000 has a pixel size 1/4 the QHY183C so a full well of roughly 3,750 electrons at a base ISO of 100. An 8 bit image is obtained at ISO1600. A 6 bit image is obtained at the maximum ISO6400. 

The 8 bit image with 1 electron or photon per color level, will have an inevitable shot noise of 1 photon. The table shows the drop in ISO range that results from the smaller pixel area. For ISO values smaller than the 8bit limit, RAW image storage must be used. 

QHY 183 dark noise 0.0024e/pixel/sec @ -15C, 0.02 @ 15C. At -15C time to 50% electron probability is 250s

Readout noise; 2.7e-@ G(0dB), 0.5e-@ G(50dB) - Min readout noise @ G(50db). 

Full well 15.5ke-@G(0db) scales down with gain. 30e-@G50. 

Gain 24db (ISO400) limit to access 10 bit intensity resolution.

Gain 36dB (ISO1600) limit for 256 grey levels in single electron increments.

At Gain 48dB 64e- full well, so single electron noise 4IU or 2% of 8bit image. Keep exposure time around 100s to minimize additional pixel noise.  Minimum 16 frame average, gets back to RMS 300 electrons for a nominal 8bit image. 

 

Over 100sec G(48db), 64e- means 1e- every 2 seconds for a full scale image.  Quantum efficiency is 84% so that's 1 photon every 2 secs. In a f11 lens 30 photons sec-1 at each of 25Mpixels over a lens aperture of 150mm diameter, which equals 2E10 photons m-2 compared to the sun at E21 photons m-2. 

Full well estimate

QHY183  has a full well of 15ke-. Working assumption is that the 1.22 um pixel has a transistor filling half the pixel 0.7 um^2. A front side illumination has 0.5 um^2 obscuration. Assuming that the area penalty does not change pixel size, and well size is simply a function of active area. We get: 

Full well ke-

                      pixel um          Exmor     Exmor R           Exmor RS

Sony a7s         8                    186.7            188.3            190.5

QHY 183         2.4                   13.4              15.0               17.1

Nikon P1000  1.5                     2.9                4.6                 6.7

iPhone14        1.2                     0.5                2.1                 4.3

The measured shot noise shows the Nikon P1000 10x slower than Sony a7s, the full well estimate is 40x smaller. 

QHY should be 4x faster than Nikon P1000, measured shot noise is very similar. Exmor RS should be a significant 

upgrade in the next Nikon P2000.

For really dim images through low f optics. (eg Elephants Trunk), 100s IS0800 f11 just visible image after 16x brightening equivalent to bottom 255 levels of a 10bit image. A 1(10bit) IU @ ISO800 is 1/8 of a photon. After 8 image average, the edge to center of the Trunk is 20IU (3 photon) with 30IU (4 photon) FWHM in poor seeing. Conclusion - just enough photons to resolve, need to maximize S/N at gain 48 (ISO6400).  Edge contrast should be around 10(8bit)IU. At 1 photon every 30 secs, Elephants Trunk is close to  the detection limit, needing 1 hr at f11. 

f2 image of the trunk will have 90 electrons so easily visible as a 160(8bit)IU @G48(ISO6400)

 

The Sony a7s has a 10x larger pixels, and roughly 10x more electrons in a full well, the key to a max ISO409K. As a result, the shot noise limited  ISO values are 10 x higher. A ISO16,000 produces a good looking  8 bit image.  However the large pixel under samples most lenses which have 1-2um resolution at the image plane.

The Sony a7s at ISO2000, supports a 10bit image, which accounts for excellent Milky Way panorama images with 20s exposure and automatic dark image subtraction. A ISO16,000 produces a 8bit image.  Elephants Trunk edge at 20 photons pixel-1 and  ISO2000  produces 20(10bit) levels, or  5(8bit) levels, and is just visible in a dark sky. When a 100mm focal length f2.8 lens is used without scanning stage, 1/2 the light makes it and  the maximum exposure time is 5s, leaving  2 photons pixel-1 at ISO2000, 2 (10bit) levels.  Needs at least 100s exposure. At ISO16000, noise is exposure time independent 1/500 to 1/5.

The Sony a7s iii uses the Exmor R version, little impact from backside with the larger pixel. 

Measured read and dark noise  at 256 electron full well  (at low read noise - Sony and Nikon only see 1 side of dist so 2x the measured Std dev)

                     Read Noise Std dev IU                Dark Noise  IU s-1  @ ISO                  

Sony a7s                 1.5                                      0.04                          @ISO16,000. 

                                                                             0.03  with dark subtraction.  

Nikon P1000           2.6                                      0.2                            @ ISO1,600 

QHY 183C                4                                         0.2                            @ 20C ISO800

                                  2                                         0.01  no dark sub.  @ -20C IS800 

Large pixel really helps, with lower read noise and much lower dark current. 

 At f11 leaving 1/30 of the light and 100s exposure, Elephants Trunk produces about 2 photons pixel-1.  At gain 36 (ISO1600) it produces 2(8bit) levels with 1(8bit) shot noise.  Stacking 10 frames get to 20 photons and makes it just visible, 1hr at f11 to collect 100 photons. Really need 300-500s exposure and guiding, or f2. Seeing and guiding noise means that f2 is the best choice. Eagle nebula better choice for high res. 

Noise can be measured as the 1 sigma  % IU of a  reference flat  white object. The short exposure time noise measurement shows Nikon P1000 and QHY183 are very similar. The Sony a7s with a 10x larger pixel area, supports a 10x larger ISO (greater sensitivity) for the same noise. Lighting conditions were for white matt surface  indoor, lit by 60w led light at 20 deg 6ft. Exposure time at ISO 1600 was 10ms. Noise is proportional to square root of ISO. The physics of light states that the noise observed in the intensity of light is equivalent to the square root of the number of photons generated by the light source. This type of noise is known as Shot Noise. At 100ms (1/10s) dark noise starts to be a factor. 

https://www.azom.com/article.aspx?ArticleID=20215

The brightness of image is proportional to ISO, so for dim objects use the highest ISO, limited by the background light level that should be set at around 50(8bit)IU. At the Milky Way reference, noise is dominated by shot noise, which in the Sony a7s  is around 5IU std dev. For a small pixel astro camera such as QHY 183C (gain 36dB), noise is around 10IU and suggests a 10 frame stack to match reference imaging. 

The strategy for dim objects is to use the maximum exposure (max photons) without blurring; stationary, scanned unguided, or guided depending on the asecs pix-1 of the optics.  The ISO or gain is adjusted so that background is no more than 50-60 IU. Stack 10 -100 frames to maximize S/N by square root of the stack. 

The shot noise scales as the square root of the number of photons. The mid point exposure in most good looking astro work is around  125 photons imaged as 125(8bit)IU with a shot noise of 10(bit)IU. The noise in the dark background is given by the square root of the IU. For the QHY 183C, the high gain (ISO800 30dB) at a 256 electron full well means that the read noise is around 2 electrons. The dark noise is 2 electron for an exposure of 100-300s, so a total of 4 electrons. Without cooling there is 10x higher noise.  This sets the practical QHY183C exposure conditions as Gain 30-36 dB,  -15C, 100-300s exposure, with at least 10 frames producing a noise of 5-6(8it)IU.

RGB image capture 

QHY183C Bayer pattern RGGB

QHY 183 cooled - 10 bit  1024 gray scale levels

https://www.qhyccd.com/astronomical-camera-qhy183/

Svbony 305  Bayer pattern BGGR for display ONLY

Svbony 30sec Dark has 4(8bit) FWHM noise - comparable to QHY which makes sense.

Capture in SharpCap .FITS 

Gain in Svbony is in 0.1dB (10x QHY) Gain 30dB (300) should be ISO800 for the RGB sensor.

PIPP - Debayer GRBG export TIFF to form frames. 

Photoshop or Autostakkert - Colour RGB. to stack frames -use Drizzle 3x. 

or

DSS - FITS select mono with Bayer pattern. imports as RGB16. Adj brightness to slope, saturation to 31%. 

https://stackoverflow.com/questions/9292947/what-are-the-latest-debayer-demosaicing-technics/24202407#24202407

https://www.astropixelprocessor.com/shop/

https://blog.cuvilib.com/2014/06/12/dfpd-debayer-on-gpu/

Video capture

1920*1080 HD Video 60FPS@8BIT

Capture video using SharpCap at 5fps 5kx4k image, 8 fps 2kx1.5k

An uncompressed video stream will require:

640×480×(3×8 bit)×30 fps=27.65 MB/s 

This is close to the net data rate I often encountered (~30 MB/s) for USB 2.0 with 480 Mbit/s devices.

The new transfer rate 3.0, marketed as SuperSpeed USB (SS), can transfer signals at up to 5 Gbit/s with nominal data rate of 500 MB/s after encoding overhead, which is about 10 times faster than High-Speed (maximum for USB 2.0 standard)

To help with the frame rate you can do one or a combination of the following:

 

1.) Use .SER for capture (as explained by dghent).

2.) Capture in 8-bit rather than 16-bit (that's probably preferred anyway for planetary work).

3.) Reduce the frame size (a smaller ROI or region of interest).

4.) Try adjusting the USB rate using SharpCap's "Turbo USB" or "USB Speed" setting (support may depend upon the make and model of your camera).

5.) Turn on SharpCap's "High Speed Mode" (support may depend upon the make and model of your camera)

6.) Try increasing the size of SharpCap's "High Speed Frame Cache" (may require more DRAM or SharpCap Pro).

Wide angle 

Sony 7a astro mod with either Visible H alpha front or UV/IR Astromik clip filter.  6mm window glass also works

100 mm Sony E mount  

20 mm Sony E mount  

14mm Sony E mount 

8mm Canon mount - fish eye 180 degree. 

 

Astro color balancing.  Clip red low, clip 1/2 green low. Color balance increase cyan and green, and adjust yellow. Increase saturation, auto color.

Wide angle HSO

Canon 8mm and 100mm lenses, back Focus = 44mm

Canon/T2 filter thickness = 24.5mm

QHY 183  = 17.5mm  works

Sbony 305 + Adaptors = 20.5mm  does not work

Orion ED80 configurations   

480mm focal length 80mm aperture f6 lens 1.4 asecs resolution.

Focus assembly only works if focus adjust is horizontal and on bottom, with roller bearings on top. Works well with Alt/Az stage. On a GEM EQ stage, need to lock focus during moves and then rotate focus assembly BEFORE unlocking and refocus. 

For full field with a7s camera, use with Field Flattener that uses 55mm (2.16") of backfocus.

480R - (2.5 to 1.5) - (1.5 to T2) - (T2 to T2) - QHY or (T2 to NEX) - Sa7s

480R - (2.5 to 2.5) - (2.5 to 1.5) - (1.5 5x T2)- (T2 to T2) - QHY or (T2 to NEX) - Sa7s

480R/5x/QHY 0.13asecs/pixel, Diff limited 0.7 asecs.

5 lines/mm = 2.6 asecs/line  MTF = 0.5 - with out 5x it is pixellated. Best solution for planets - need Svbony camera 

7 line/mm   = 2 asecs/line      MTF = 0.25

Svbony 305         480mm 5x   FWHM = 2.0 asecs  based on  MTF with 5x essential.

480R/5x/Sony a7s pixel limited. 

Distance from telescope face to camera face at focus is 6" (150mm). 

Sun using ND filter and Ha filter with QHY 183M camera. Field of view 1.5deg 1asec/pix. Gain 10 & 10msec exposure. 20% of 200 frames with sharpening produces plenty of surface detail. Solar prominences not visible. 

Celestron 6 configurations

Position of secondary mirror 

Screw the secondary mount back with notch at 3 o'clock.  "The needed alignment cues are the edge numbers at 3:00, and a fat sharpie stripe on the edge of the actual secondary mirror, also aligned to 3:00. If nobody removed the secondary mirror, it should be in that position when the collimation screw above the word Celestron points to the top of the scope."

Check collimation 

Use artificial star 50 um (0.7 asecs @ 16m), Sony a7s camera for SCT & RASA. Turn Menu - Tracking Mode OFF.

Collimate using artificial star indoors at around 16m distance. Defocus star - Find screw close to narrow point - Loosen other 2 screws - Tighten close screw. Rinse and repeat - Success when out of focus is symmetric. 

Check HFR in phD2 for spot size. 4.5 pixels = 1.3 asecs in QHY camera 0.3 asecs/pix . 

SCT Back focus distance from primary mirror baffle tube lock ring (in)

C5      5 in

C6      5 in

C8      5 in

C925  5.475 in

C11    5.475 in from 3 in-2 in Reducer Plate 5.975 in from 3 in Primary Mirror Baffle Tube Lock Ring

C14     5.475 in from 3 in-2 in Reducer Plate 5.975 in from 3 in Primary Mirror Baffle Tube Lock Ring

https://www.celestron.com/blogs/knowledgebase/what-are-the-optimum-back-focus-distances-for-celestron-scts

SCT theory

Lens resolution can be measured as spot size FWHM or Half Spot Diameter, MTF of l/s = 0.5, or 2x edge width 75-25%. Line width equal to FWHM equivalent to  MTF0.4 or 4x Rayliegh limit  (MTF0.1)

For a 150mm optic such as C6 that is <1.5 asecs @ MTF 0.5  

SCT-QHY 

Field 0.275 deg 0.19 asecs/pix

Resolution 1.7 asec l/s clearly visible 1.3 asec just visible. Test  using PHD2 -  HFD 4.5pix = 1.4 asecs. See comparison with P1000 below. Need to adust color temp and tint in Camera RAW filter for best color rendering at edge. Sharpen produces clean 1asec wires.

SCT - Svbony 

SCT  T2 extension - 20mm T2 - 30mm T2 - Svbony = 5" backfocus to camera chip

Direct spot image FWHM 1.2 asecs.

SCT - 5x - Svbony 

SCT  T2 extension - Filter F to F - 20mm T2 - 15mm T2 - Nose female - 5x - T2 adaptor - Svbony  5.5" back focus to 5x face.

Measured 0.055 asecs/pix  MTF @ 2.6 asecs/line  =  0.7, FWHM = 1.4 asecs.

Deep sky set up 

C6 SCT - Long T2 adaptor-50mm T2/T2 - QHY183. Position USB on RHS for correct orientation. 

Align red spot 

Align 400mmR lens - 15mm T2/T2 - T2/SonyE mount -  Sony a7s. Camera at +45 deg. Zoom box align point bottom right. 

Tracking 400mmR lens - 25mm T2/T2 - T2/Svbony 

Hyperstar theory 

Telescopes receive plan waves from a distant source. Resolution is a simple function of the lens aperture. 

Hyperstar images light at the focus of the main mirror so operates like a microscope objective receiving light from a wide angle. The resolution of the system is limited by the Hyperstar  and is a function of NA.  The HyperStar systems are not diffraction limited and are designed to produce a spot size roughly 2.5 times the size of the Airy disk. The Airy disk of f2 optic is 1.7 arcsecs.  Therefore the design limit of Hyperstar is FWHM = 4 arc secs. 

Spot size for a 128IU spot is 4.5 asecs in the example image on Starizona site.   

With QHY 183 camera C6 RASA has 1.7 asecs/pix. 

https://www.edmundoptics.com/knowledge-center/application-notes/imaging/limitations-on-resolution-and-contrast-the-airy-disk/

https://www.cloudynights.com/articles/cat/articles/the-amazing-hyperstar-a-guide-to-optimize-perf-r3013

Hyperstar 6 

  • Backfocus (from mounting thread to focal plane): 39.8mm (1.567")

  • Modular Filter Slider height:  22.2mm - newer rev 17.5mm.

  • Camera side thread 1.75 inches x 32 UNS-2A?.

  • QHY 17.5 mm   - 1.1 asecs/pix image res -Best resolution NO SPACER.  Manual says Net 5mm (3/16")..."You need a 4.8mm adapter"

  • Sony a7s 18mm backfocus.

Hyperstar collimation

Screws with white washers on HyperStar rotate camera as desired, tighten screws.

Long screws are PUSH, short are PULL. Push one, pull another see if collimation improves. 1/4 turn at a time.

Use cable tidy to id direction.   Loosen ant-clockwise the 3 taller collimation screws (back them out maybe a few turns).  Then clockwise  tighten the short collimation screws, BUT, be careful because there is a slight angle between the two bottom rings on the HyperStar.  If you tighten one screw down before the others it can tilt those rings.  I run each screw gently down until each one just touches.  Then you can tighten all three.  Then just run the taller screws back down until they are tight and you will be back in the default position.  Starizona

Aim lens vertical so no side load on adjustment. Use Tri-Bakinov mask to create diffractions lines. 

Long screw is hold - release, and then twist short till lock. 

Pick bright star in center, adjust exposure so it almost saturates at gain 10. 

Should see 2 diagonal  groups of 3 lines, symmetric and centered. 

Adjust and refocus. 

Once center good, check 4 corners, identify plane in error. 

Remove mask. Check HFD or FWHM = spot size in pixels.  1.1 asecs/pix.

Documented performance

The larger apertures Hyperstars have longer focal lengths (C14 2X C6), so pixel resolution is 2x smaller, but the microscope resolution (f number) is the  same from C6 to C14, around 4 arc secs FWHM is the practical resolution of the Hyperstar. 

"With good guiding and careful focus, the HyperStar produces tight, round stars over a large field. With my C14, I typically see minimum FWHM star images in the range of 2 pixels in a stacked image, which translates to 12.8 microns or 3.9 arc-­‐sec"

https://www.cloudynights.com/articles/cat/articles/the-amazing-hyperstar-a-guide-to-optimize-perf-r3013

Comparison C11 Hyperstar 4.2 arcsecs FWHM, Edge 3.5 arcsecs FWHM. Very similar - probably seeing limited. 

https://www.astrobin.com/full/i21oxh/0/

Starizona C11 reference resolution Leo Triplet   1800 pixels = 35 arcmin, 1 pixel = 1.1 arcsecs.   FWHM = 3.3 pix = 3.5 arcsecs. 

Starizona C6 Whirlpool 4.9 asecs FWHM. Example image Starizona from7x7 asecs edge to edge = 3.5 asecs FWHM

GOAL around 3 pixels FWHM looks like a digitization limit. low 4's arcsecs FWHM,  

Resolution test:  3 arcsecs FWHM = 1/2 pitch is 50% MTF  =(Imax-Imin)/(Imax+Imin)/ MTF(0) . 

No spacer, set neutral. Measured in house, with target and artificial star at 16m. No atmospherics.  

lw asecs     MTF

12.9            0.90

6.4              0.67

4.0              0.47

3.2              0.36

2.6              0.20

HFD (Half diameter) using artificial star indoors and phd2  = 3 pixels = 3.3 asecs. Clearly resolve 2.6 asecs with sharpening. Convert to SCT and then reinstall HFD measured as 2.5-3.5 HFD. 

Nikon P1000 configurations

Nikon P1000  12,000mm  =2.2asecs, MTF = 0.5    0.8 asecs diff limit.

                           3,000mm  =2.4asecs, MTF = 0.5   @ 0.6asecs/pix

                              100mm  = 60asecs, MTF = 0.6

At 12,000mm = 3000mm + 4x, 1/200s ISO100, clearly resolve 1 asec (10 pixel) wire in early morning with cool calm air. At 3000mm measured 0.4 asecs/pix, at 12,000mm 0.1 asecs/pix. Rayliegh line res 0.8 asec  @ MTF 0.1

400mm refractor  Pentax thread

Svbony 305         400mm FWHM = 6 asecs, based on autoguide HFD 6 pix @1.1  asecs/pix

FHWM summary

                               FWHM asecs      asecs/pix     at MTF = 0.5 (0.3)

400mm Pentax/Sa7S       6                     2.6         confirmed by phd2 HFD

C6 RASA/QHY                    4                     1.1       confirmed by phd2 HFD and Baktinov screen

480mmR/FF/Sa7s             4                     2.3                               

480mmR/5x/QHY            2.3                   0.22   

Nikon P1000                    2.2                    0.4      5x optical reduces to 0.1 asecs/pix

C6 SCT/QHY                     1.6 (1.4)           0.25  HFD = 6pix = 1.8 asecs         

C6SCT/5x/Svbony           1.6 (1.4)           0.05 over sampling to resolve 0.5 asecs Saturn ring gap

Lucky Imaging 

Guidelines for lucky imaging on stars based on paper. Sampling frequency needs to be around 30 Hz. For a 200 sec reference exposure that is being auto-guided. Pixel resolution around 1/2 FWHM is borderline under-sampling, use drizzle to provide improved grey scale. Starting with the seeing resolution,1% selection will improve resolution 2.5-3x or to diffraction limit, whichever is larger. 10% selection will improve 2-2.5x. Need low noise image collection, with no compression and maximum bit depth. Total image time of 200 secs at 20 fps = 4000 frames, 1% = 40 frames.

https://arxiv.org/pdf/astro-ph/0507299.pdf

For planets, use 2 or 5x image to get sufficient image sampling, collect 4000 frames (in 2 mins for Jupiter). Need seeing of 2 asecs or better, to get to diffraction limit.  In theory could get C6 as good as C14 example !!  Worth a trip to McDonald observatory.  

Player One Uranus-C IMX585 as capture camera. BSI technology zero amp noise. 2.9um pixel. High frame rate for lucky imaging2k images at 105 fps. $400.

Svbony 305 IMX290 130fps @(320*240)

Test 

Artificial star nominal FWHM 0.6 asec  (50 um at 16m)

With AC off, HFD 1.5 asec, midrow FWHM 0.9 asec, image 1.26 FWHM

With AC on, artificial star at 75%

8 ms G322                                          10% 1.38  (too noisy)

12ms G275 FWHM    5% 1.4asec    10% 1.30 asec    20%  1.25 asec  100% 1.45 asec (align helps)

24ms G228                                         10% 1.53  (sample too long)

0.3s                                                               1.65  star dimmed

At much brighter artificial star and  lower gain, the flat topped profile shows the finite source size.  Measure the log slope of the intensity profile, a 10x change in intensity gives 2xStd Deviation = FWHM 

Calm - no AC

10ms 10%   1.24 asecs

Artificial seeing - AC on

10ms 5%     1.25 asecs     - Gain 0.2dB  so low noise.

10ms 10%   1.38

10ms 100% 1.84

0.3s              1.69 asecs

Artificial star 0.6 FHWM, calm air  FWHM 1.3 asecs, so Lens contribution 1.1 asec FWHM. Lucky sample reduces spot size by 0.8x. 

For profiles use :

https://ij.imjoy.io/

Lucky imaging reduces seeing FWHM from 0.4 asec to 0.1 asec, but does not eliminate. Balance sampling noise for short exposure/high gain against lucky sampling. Align gains a bunch, lucky sample an additional 20%. 

Guidelines - time <10ms, G<300, 10% sample.

Planets

Mars: 5 mins max per video, 15 mins total for all videos you intend to combine

Jupiter: 1 min per video, 3 mins total

Saturn: 3 mins per video, 10 mins total

For longer collection than  total,  de-rotate block stacks in  WinJupos.

https://www.skyatnightmagazine.com/astrophotography/astrophoto-tips/use-winjupos-derotate-planetary-images

Jupiter $ Saturn  11/1/23 with C6 seeing 3/5 on a cold night 40'sC.  21ms exposure, Gain 94 Jupiter Gain 281 Saturn. 1.5 asecs FWHM. Saturn ring edge = 0.6 asecs. Seeing blur radius 8 pixels = 1.6 asecs FWHM. Best results with 10% of 10k frames, follow with Sharpen - Normal focus.  With 100% frames, noise level around 3 asecs, Sharpen - Focus very blurry can recover much of the detail. 

A 20 asec object (Saturn) @ 1 asecs resolution after lucky imaging is just acceptable. So for long exposure without lucky imaging, 2 asec seeing should just support a 40 asec object. RASA resolution of 4 asecs, should just support a 1.2 min object.

 

Excellent C8 & C14 results with 8ms exposure gain 342 for C8 Jupiter or 70 fps C14. - FWHM 0.4 asecs.

Reference Telescopes 

The most common amateur solution uses video which is always compressed.

Jupiter example for C6  uses avi for 2 minutes at around 160 fps, and is under-sampled. 

C6 has 0.2 asecs/pix  Res 1.0 FWHM, diff limit line 0.4 asecs,

C9.25  0.55 asecs/pic - FWHM = 2.2asecs probably seeing limited. 

C8 2x has  0.07 asecs/pix, edge = 2 pix = 0.3 FWHM based on Saturn image. 0.28 FWHM diff limit. 

C14 has 0.1 asecs/pix, edge +-25% = 2 pix = 0.4 FWHM, diff limit line 0.2 asecs FWHM.  

Hubble Wide Field has  0.05 asecs/pix, HRC 0.025.  image has 0.03 asecs/pix, edge +-25% = 2 pix = 0.12 FWHM, diff limit  0.025 asecs FWHM, Design spot size = 0.1 asecs. Confirmed by Saturn outer ring space 0.1 asecs clearly resolved. 

Webb - 0.009 FWHM diff limit - 3x better than Hubble, design around 0.1 asecs. Edge 2 pix = 0.02 asecs = 0.04 asecs FWHM.

Chile adaptive optics 0.08 asecs FWHM.  https://arxiv.org/abs/2008.01364

RASA systems

C8 Hyperstar specification 400mm focal length, spot size  4.6 um RMS = 1 sigma, or FWHM 4.7 asecs. - HFR = 2.7 pix. 

C9.25 Hyperstar  FWHM =  5.4 asecs.

C11 Hyperstar specification 620mm focal length, FWHM 3.0 arcsecs.  4.2 arcsecs FWHM, Edge 3.5 arcsecs FWHM.

C14 Hyperstar 3.9 arcsecs FWHM,

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Celestron C6  SCT  / 5x / Sony7as

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Phone

For astro/northern lights - need max resolution pixel and bit depth. 

48MP 1x Main: 24 mm  60 deg FOV  30arcsecs/pixel / 30 arcsecs optical resolution, ƒ/1.78 aperture, second-generation sensor-shift optical image stabilization, seven‑element lens. 12M image under-samples..  Better than Sony 7a 20mm resolution. Best choice for Northern lights. 

Turn on PRO RAW, stores 10 bit, 48Mpix image.

10 sec on tripod max still exposure time, use for stills - that is the limit before stars start to trail due to rotation. 

Milky Way time lapse -

8-20mm Sony 7as  - 30s @3200 = 65 sec cycles = 1 frame every 10 arcmins of motion. Compress to 20 fps for smooth action. Make corrections to RAW files. Use Photodirector - 0.02 per frame. 45 mins of 8mm lens = 2 secs of video.  2 hours for 30 degrees of motion.  Need battery extender.

iPhone14 Night mode - on tripod.  Much noisier than Sony RAW. 

2 sec max time lapse video exposure time, 30 deg FOV. NightCap time lapse for longer exposures. store TIFF limited to 12M, use for time lapse, so 30 sec exposure time limit. 

Aroura time lapse

Sony a7s 20mm f2.  Aperture priority, ISO 12800, +- 0 exposure, WB temp 3800K for dark sky. RAW image, no long exposure NR (no dark frames), Multi zone exposure control. Display -2.  Kp =1 requires exposure 15s.  At 30 sec cycle, 10 min exposures gives 20 frames. Time lapse 0.1 s per frame with 0.03s cross merge = 2 sec of 10 fps video with 300:1 time compression. 

System Performance 

 

Measured resolutions summarized below are consistent with these limitations.  Light 1 arcmin, post 25 arcsecs, wire 1 arcsecs. Gap in post 30 asecs, Perforation in post 10 asecs. 

                                                                                                                     FWHM      Diff limited

Focal length Aperture  f number    Mount         Back Focus  Camera    Measured  Resolution      PIxel res

    mm                mm                                                   mm                          arcsecs       arcsecs

8mm                                 f3.5         Canon EF      44mm       Sony7as      250                              250

20mm                               f2.0         Sony E           18mm       Sony7as       60                               100

20mm                               f1.7                                                  iPhone 1x     60                                 30 

35mm                               f3.5         Pentax M42  44mm      Sony7as        40

100mm          50mm       f2.8         Sony E           18mm       Sony7as        14                                 20

100mm                             f2.0         Canon EF      44mm      QHY                20                                  6.0

300mm        150mm       f2.0         C6 RASA T2   39.5mm   QHY/Svb         4             3                   1.7       diff limit = 1.75asecs, design 3asecs

400mm           60mm      f6.5         Pentax M42  44mm        Svb                 4             0.95             1.6        pixel limited ?

480mm           80mm      f7.0         Orion T2        55mm       QHY/Svb         3               0.7               1.1 

480mm           80mm      f7.0         Orion 5x        55mm       QHY/Svb         1.8            0.7               0.22              

539mm           70mm      f6.5                                Fixed         Nikon 1000     1.2            0.8               0.12      extrapolated pixels from 0.6 asecs/pix. 

1500mm       150mm      f10          C6       T2        127mm       QHY/Svb        (1.2)          0.4             0.6         1.7x sample  observable pixelation

1500mm       150mm      f10          C6       T2        127mm      Neximag10     (0.6)          0.4             0.3             

 

1500mm       150mm      f10          C6 5x Emount                 Sony 7as         2.0            0.4             1.0  

1500mm       150mm                      C6 5x T2                           Svb                  1.1             0.4             0.06      Target set up for planets. 

C14 4kmm     350mm                                                                                         0.4          0.32          0.06

Hubble            2.4 m                                                                                            0.12        0.025       0.05

Adaptive earth optics                                                                                         0.08

Webb               6.5m                                                                                             0.04        0.009       0.009

8mm Fisheye / Sony 7a   180 degree 3500 pixel  = 180 arcsecs/pixel, with Manual transform 150 degree, with PS auto Fisheye correction  85 degree field. 

Line up the full Milky Way with the long axis. Exposure time 60 secs untracked. Excellent focus with glass insert. FWHM = 2 pixels in RGB cell = 250 arcsecs.

Requires 2 shots @90 degrees for full 360. With foreground, set horizon, take 4  shots vertical stitch if MW directly overhead. Need filter for Ha line.

8mm/filter/QHY == 20mm/Sony 7a 90 degree FOV.

100mm/filter/QHY == 200mm/Sony 7a

SCT is 10x better resolution than RASA.

MILKY WAY

 

Photographing the Milky Way requires largest possible field and f number, a 20mm focal length f2 full field lens allows a full sky mosaic with around 40 images 94 degrees per field. A 20 sec untracked exposure at 2000 ISO on a astro mod camera images stars down to magnitude 10, and many nebulae.  A 8mm fisheye lens mirror compatible lens will allow filters  with a 2.5 um pixel camera QHY, will give  90 degree field of view and enhanced color contrast Milky Way. 

Basic nebula = 30s ISO2000 with 5x to reduce noise. For low intensity nebula of whole MW add 3x  105s @ ISO6400, f/2. or 10x more exposure, needs v dark skies such as Grand Staircase Escalante NP and scanning stage for 20mm lens. 

NEBULA 

The nebula within the Milky Way are some of the most visually interesting features with sizes from several degrees around Orion, to 10's of minutes.  The longest reasonably priced f2 refractive lens is 100 mm with an aperture of 60 mm and an abberation  limited resolution of 15 arcsecs.  Lenses are designed for a full frame sensor, most of which have insufficient pixel count to match the lens resolution.  Reduced field sensors (1/2 frame) can resolve closer to  the limit of the optics, so a nominal  "100 mm" f2 lens with 1/2 frame sensor has a field equivalent to a 200mm with 7 arc secs per pixel resolution. A larger (400 mm) focal length f2 telescope is available with a Schmidt Cassegrain telescope in Rowe Ackerman configuration where the secondary mirror is replaced by correction optics and imager so the focal length is solely determined by the main mirror. Resolution with the correction optics is 2 arcsecs, paired with 1/2 frame sensor.  Based on a 20 sec exposure, crude alignment to within 1 degree is fine.

Exposure strategy for highest resolution.

Benchmark f2 lens 20s @ ISO2000 for a dark sky Bortle 1-2.  400mm f6 requires 10x more exposure, C6SCT f11  requires  30x more exposure.  For C6SCT with QHY183C, G50 (g10,000) produces  5x. 120s exposure produces 6x. A total of 30x, offsetting the optical loss. To reduce noise, need multiple (>10) samples to reduces random noise 3x. Dark frames will  reduce systematic noise from chip, a fan from the mid right side of the chip. 

Hubble palette 

Using HSO 8nm  line filters the intensity is 1/100 compared to RGB filters that have a 150 nm bandwidth.

Milky Way   8mm Canon mount with Canon-T2 filter adaptor and  QHY 

Nebula in context  100mm Canon mount  with with Canon-T2 filter adaptor and QHY 

Nebula close up C6 RASA  f2 lens combined with QHY cooled camera.

 

Gain 30 (6400ISO) and 200secs exposure gets to similar signals to Milky Way  reference conditions. An additional 10x in exposure time, requires 30 arc min (60 pixel) alignment to the pole star for tracking which  implies reasonably careful align.

GALAXIES

C6 RASA f2 lens with Svbony camera has  using  1.5 degree field 70x20secs @ 6400ISO or equivalent good for Whirlpool, and Leo Triplet. Stars with magnitude 10 just resolved.  Most deep space objects  are relatively close to pole star axis and make align to axis less critical. RGB and Ha composite image makes for a really good look. Andromeda needs larger field QHY camera with RGB filters or 2 stitched Svbony  fields. 

LENSES FOR PLANETS

The planets are much higher brightness and much smaller (20-40) arcsecs, so resolution is the key requirement.  

C6 Prime with Svbony, ideally with 5x to get lucky image oversample. 

For Jupiter 2 mins of exposure before rotation blurs. 133 pixels across, 10 hr for full rotation, 133 pixels in 5 hrs = 2 mins per pixel. Example 2 mins avi at 160  fps. Using avi will invoke compression, try 16 bit image stores. Brett Turner 300 pixels. 5x would get there. 

For repeat exposure set autotimer = 2*exp time + 10 / delay 5

FILTERS

Optolong L-Ultimate 2" Filter

The L-Ultimate is similar to Optolong's L-eNhance and L-eXtreme filters in that it is a dual band filter that allows the transmission of Oxygen III and Hydrogen Alpha wavelengths, but the L-Ultimate only allows a 3nm bandwidth, compared to the 7nm of the L-Extreme!

NORTHERN LIGHTS 

Extra batteries for cold.  

20mm or 8mm lens around 30 sec exposure, tripod essential. Sony 7a - can take video - no time lapse high ISO or iPhone RAW.

8mm/Sony7as  full 180, need two images at 90deg. For foreground, place horizon at middle, 3-4 images stacked vertically to get overhead. 

For slow moving Aroura - use iPhone time lapse - top arrow, adjust exposure to 2 sec. Need to change "preserve settings"  - Night in System.

For fast moving Aroura - use 8mm with video or iPhone  video. 

STAR FINDER

https://nova.astrometry.net/

Login select amazon

GEM stage implementation

For long exposures the telescope must scan in sync with the earth. The German EQ (GEM) stage has a Right Ascension axis that must be aligned with earths axis and a Declination axis at right angles. 

Telescope location requires visibility to Polaris and Target. 

In Austin, at patio pillar - see 10 degrees north to 30 south, 10 degrees West to 40 degrees East 

In Austin at hose bib - see 0 south to 30 north, 30 degrees West to 20 degrees East 

 

In Wimberley, lights to North 

In Junction TX, park lights to North and East 

In Junction TX, AirBnB lights to South and East.

Polar align 

The RA axis is aligned the earths axis using a camera that is mounted to the RA. The RA is rotated to find the center of rotation. The camera is also used to find the earths rotation axis which is close to the pole star. The Altitude and Azimuth adjustment is use to align the stage axis to earths axis. 

The Polemaster camera is sold by QHY for the polar align process, with a 10 degree image field. A cell phone camera is a convenient way to place the polestar in the Polemaster field. A cell phone clamp is used to mount the cell phone to the stage. 

Polemaster process

Find polestar using cell phone camera  app

Center polestar in App window 11x9 degrees wide

Follow instructions to find stage center by moving polemaster mount. Start at -60 then 0 then +60 to eliminate any square error in Polemaster to RA axis. 

Check stage axis by lining up red icon and polestar - rotate polemaster arm - 10 polemaster pixel error = 2 arc min.

Check camera align by pointing at polestar and rotating camera theta. 

Align stage center to polestar (Rough align) within  4 arcmins - 0.01 arc secs/sec star drift 

Earths axis is 44 arc mins from polestar (https://astronomy.stackexchange.com/questions/38469/the-position-of-polestar) 1/3 of the way from polestar to lambda Ursa Minor. 

Align stage center to earth axis (Fine align red to green boxes) up to 30 arc secs (single pixel) - 0.001 arc secs/sec drift

AVX use model 

Configuration

Mechanical : Telescope & cell finder mounted to AVX, plate to 400mm + SVBONY guide camera & Polaris finder mount.

Electrical: AVX Handset USB to lap top USB; Polemaster, QHY and SBONY to USB hub to lap top USB2. SBONY guide ST4 to AVX St4.

Power; Mount to Battery 12v, QHY cooler to Battery lighter.

Software :  CWI controls AVX mount, NINA controls QHY, PHD2 controls SVBONY & AVX guide, Polemaster controls Polemaster camera.

Align Components

Align guide and Polaris finder to Telescope using local reference.  Polaris is an option.

In a 2 degree field; Polaris, Rotation axis, stage axis all will be visible. Set tracking off, gain down, exposure long and create star trail. Then slew RA to see stage axis. 

Align to Stars

Connect Hand controller and QHY/NINA to USB hub to Laptop

Connect Svbony to Laptop

Use Handcontroller

1) Index

2) Star Above. Use phone to identify brightest star overhead. Use laser pointer to align telescope

3) Single star align Align Stars - bright and directly above 

Use Cell phone to find target, then telescope, keep adding references closer to the target so the key pas works and the align gets better.

Spring 

Arcturus in  Bootes

Spica  in Virgo 

Regulus in Leo 

Summer

Vega in Lys

Altair in Aquarius

Deneb 

Arcturus in  Bootes

Fall

Altair in Aquarius

Deneb

Capella in Auriga 

Stephans quintet in Andromeda 

Winter

Sirius in Canis Major 

Capella in Auriga

Rigel in Orion

Procyon in Canis Minor

Pollox in Gemini

Betelgeuse in Orion

Aldebran in Taurus

Reboot PC, cycle mount, reconnect USB.  

Restart using Last Align so mount does not move.  

Check pole align 

To measure pole align errors, skip star align , and use QHY with PHD2 in "drift mode". 

Celestron PECTool for summing PEC runs. 

Mount design RA worm gear with period 480 secs or 8 min cycle, so need at least 24 mins to get a drift trend.

Nominal  PE stage performance +-15 asecs, improved to +-2 corrected.

https://www.darkframeoptics.com/blog/mount-performance-charts-1

Baseline test using 480mm lens 1.5 asecs/pix - 30 sec exposure with drift of 0.04 asecs/sec produces 1 pixel error.  5% of the worm cycle. This will be good enough with f2 RASA optics with 2 asecs resolution. 

To preselect section of worm gear, UTILITIES/MENU/RECORD/ENTER/ENTER - indexes the worm gear. Target will be somewhere in 2 degree window.

Position directly up - measure Az error using drift feature, northerly drift  = error west of pole.  Use for high accuracy cyclic RA worm error. 

Position to E or W  - measure Alt/tilt error using drift feature, northerly drift = error north of pole. 

Position on Polaris - pick edge star with 0.15 asecs/sec untracked error. and run for 24 mins  to measure  RA, PEC and scan rate error over 600 pix with 0.1 asecs/pix resolution with no DEC axis contribution. 

https://astrocamera.net/equipmnt/p-align/drift.htm

Position directly up comparing 2 stars E and W of meridian. flipping RA and DEC sides. Collect images and find difference in RA for stars on equatorial - difference in RA is 2x orthogonality between RA and DEC.  http://company7.com/library/techin/orthogonality.html

Stage 

Analysis of tracking errors gives an idea of underlying causes. Unguided, the DEC axis is fixed so after removing linear drift from pole align and orthogonality, the residual RMS or Standard Deviation is a quantitative measure of the combined seeing and star analysis errors, and their impact on spot size. In most cases seeing dominates, so "seeing limited" star spot size FHWM = 2x  RMS or standard deviation. In Austin in summer,  the estimated seeing  limited spot size = 0.9 asecs FWHM.

 

For my AVX stage with 400mm lens & Svbony camera , the contributions to unguided RA error over a 480 sec worm gear cycle  after careful Polemaster align are;

      Raw = 2.6 asecs RMS or  +- 8  asecs 3 sigma - consistent with specification

      Pole align error contribution = 9.6 asecs p-t-p

      Worm gear contribution = 3 asecs p-t-p

      Non random 10 sec exposure = 4.5 asec p-t-p  30-50 sec period

      After non-random  error removal = 0.72  asecs RMS 

      Seeing = 0.45 asecs RMS based on unguided DEC.

      Residual random position error =  0.55 asecs RMS - probably best that can be done !

The resulting uncorrectable spot size from random positioning errors with perfect seeing  = 1.1 asecs FWHM.


The most common solution is using a guide telescope to remove both pole align error and any systematic motion errors. Guiding programs such as PHD2 have measured sub pixel  noise ( 0.3 pixel RMS)  detection of star motion by following the shape of the image of a star.  Best performance guiding needs a guided telescope and camera with similar pixel and optical resolution to the imaging telescope and camera. 

For my AVX stage guided using 400mm lens with Svbony camera  with resolution of 2 asecs FWHM, over 480 sec, with  1 sec exposure.  

           RA raw error = 0.83 asecs RMS  random that produces a  star spot size =  1.6 asecs FWHM.

           Worm error = 0.3 asecs p-t-p

The guided raw error is slightly larger than the unguided random residual, suggesting that guiding may be over correcting on noise. Guiding corrects systematic errors, attempting to correct random errors will just increase total error. increasing exposure time will  tend to average out random position errors.

This also shows guiding within 2x of seeing RMS. The seeing error can be  reduced by increasing exposure time averaging out the seeing. A 4x increase in exposure should produce a 2x improvement in noise and guiding. Another strategy is to use multiple stars so that independent random variations in each star average out. Same rule should apply 4 stars should produce 2x noise reduction.   

For the AVX stage, the practical limit to best resolution in long exposures is probably FWHM of around 1-2 arc secs. A 30 sec unguided exposure has a good chance of matching guided. 

There are alternatives with improved RA accuracy, but their tracking performance is still  limited by the alignment to the earths rotation axis.  A dedicated RA scanning stage such as the Fornax Lightrack, uses a drive on the end of a long lever to achieve a RA tracking accuracy of +-1 arcsecs over 8 mins. It needs an additional RA & DEC axis  stage to point the telescope, so there is no star find capability.  A $5000 stage such a Fornax EQ mount has a claimed full cycle error of  +- 6 arc secs. The addition of a high accuracy encoder (Telescope Drive Master) can achieve +- 1-2 arc secs.  

Two modes; open loop (unguided) and guided. 

Unguided; if using CWI make sure that Siderial rate is 100%.

Residual error tests; hand controlled  0.04 asecs/sec, Supports 30 sec exposure with Orion ED 80 with QHY - 1 asecs/pix. 

Guided

Off axis guiding will not work for RASA f2 configuration.

On axis guiding - use the Orion ED, Pentax 400mm or 100mm lens  as a piggy back guide scope on the Celestron.  

Use a mono uncooled camera.  LH uses Orion 60mm guider 240 mm focal length  32 oz. 

 

400 mm pentax lens /  M42 to T2 / 20 mm T2 /T2 to C/ SVBONY SV305 Pro Telescope Camera, 2MP USB3.0 Astronomy Camera, 1.25 inch Astronomy Guiding Camera  2 degrees 2 asecs/pix.  - Mount to shared plate with Telescope.  Vixen bar to base of shared plate.

https://www.bhphotovideo.com/c/product/852654-REG/farpoint_fvs_vixen_style_saddle.html?msclkid=34918e6f86e51b9f92a5ec1ad0508ca5  $89.00

100 mm lens - QHY as finder/guider 11 degrees, 7 asecs/pix.

Polemaster as a finder  11 degree field - 30 asecs res. 

https://www.admaccessories.com/product/dpa-pole-d-series-dovetail-adapter-for-polemaster-mounting/

stage errors.jpg
Unguided ATX.jpg
Guided ATX.jpg

AXT test results  March 22 

Unguided 480 sec

Measurement DEC noise 0.45 asec RMS = 1/3 pixel

DEC was at neutral balance point showed 7 asec of backlash 

Drift 0.02 asec/sec  at limit for Polemaster 

Residual  RA RMS 2.6 asec 

RA PEC after 120 sec rolling average = 3 asec p-t-p, similar to pole drift, error is low when PEC is in opposite direction to pole drift. 

30 sec exposure RA 1 asec RMS - high res

120 sec exposure RA  2 asec RMS - f2 RASA PEC will help 

Unguided DEC

Error after linear = 0.45 asecs  - measures seeing and detection effects 

Unguided RA 

Error raw = 2.6 asecs RMS

Error after linear = 1.6 asecs RMS = +- 5 asecs 3 sigma

Worm contribution = 3 asecs p-t-p

Error after worm = 0.77 asecs RMS 

Subgroup 10 shows non random = 4.5 asec p-t-p  30-50 sec period

Error after sub 10 = 0.72  asecs RMS  - no obvious non randomness left.  

Contributions - Seeing 0.45 asecs RMS, random position 0.55 asecs RMS

Unguided 30 sec for high res (1 asec / pix), 120 sec for f2 RASA - add PEC

Guided 480 sec - 1 sec period.  

RA = 0.83 asecs RMS  mean zero - 1.6 asecs FWHM.

Subgroup 10 shows random variation (10 sec exposure) 

Worm contribution = 0.3 asecs p-t-p

Good enough for RASA and Galaxies.

At 1 sec exposure - 10x reduction in systematic, 15% increase in random. 

Need to increase the exposure time.  

Place DEC out of neutral balance to avoid backlash steps.

Make sure that camera axes match the RA - DEC directions... better calibration

in the case of standard deviation, the mean is removed out from observations, but in root mean square the mean is not removed. however in the case of noise where the mean is zero, the two concept are the same.

For 400mm lens aperture 70 mm aperture Dawes resolution = 0.7 asecs = FWHM  

Align results July 2022

C6 Hyperstar w. QHY 183 RT =  1.7 asecs/pix.  Drift = 0.1 asecs/sec or 30 sec unguided limit. Background G30 (3200 ISO), 6 sec exp, B = 61 IU(8)  FWHM = 4 IU(8). B/N = 15 & 1.4E-3 iso-1 sec-1. Smallest star FWHM = 3.4 asecs with poor (1.5 asecs dither) seeing and observable mis-collimation. 11Mag stars are saturated S/B = 4. Need to correct collimation. Basically performing to spec !

Fornax use model 

Fornax with  3 axis Manfrotto stage. R axis on RA plane. Tilt 1 provides DEC axis. Tilt 2 fixed at 90. 

Orthogonality error limits scanning to 0.1 asecs/sec. Accepting a 2 pixel scan error:

        100 mm lens and Sony 18 asecs/pix so up to 360 sec   

        100  mm lens and QHY   7 asecs/pix so up to 140 sec, sets limit for line filter imaging. 

         480 mm lens and Sony  4  asecs/pix so up to  80 sec, works fine with 30 sec max in the Sony.

Jupiter_with_Lucky_Imaging.jpg
Elephants trunk.jpg
Jupiter close.jpg

HSO  filter image

Ha filter requires 50x more exposure 8nm filter vs 300nm for White=  37x wavelength reduction.

 

Filter changer - 

1L/2S/3H/4O/5 clear

30s crude align 

120s needs fine align.

Calibration frames

Bias - readout noise - lens cap and short exposure

Dark - system noise - lens cap and same exposure time as lights (images)

Flats - vignette - white tee shirt over lap top screen.

Dark flats -noise on flat - lens cap with same exposure time as Flats

Collect at least 10 long exposures, with dark flats.  1/4 and 1/10 times for HDR.

Stack images in Deep Sky Stacker - group the different filters and exposure times, stack repeated images  using a common reference selected from best H image. Take non repeating images, use same reference frame, check images in turn and save. Use separate groups for different image sets that DO NOT include reference. 

In PS assemble HSL layers, change mode to RGB, align, equalize core color area, paste into RGB layers. reset black level, separately merge HDR color images, then merge color and L shorter exposure times.

Exposure times 

f2 30secs ISO2000 RGB is benchmark for good nebula =  

Filter increases exposure 500x, reduces bkg 6x.   

G30 is ISO 6000 so f2 240s G30 HOS should resolve M8. 

Example Rosette Nebula HOO image   f2  120secs x 4 frames per channel.  In Wimberly S/N  for Nebula 2.5:1, a 2x improvement with line filters for a M5.5 nebula, background 4 AU. Eagle nebula (pillars of creation M6.0 should increase exposure time to 200 secs. The nebula had a intensity of 10 AU, so darker Bortle or longer exposure for dimmer objects. 

 

Example Orion Nebula using 400mm f7 (1/10x) 120s G30 HOS filter = partial Orion nebula bkg 7, nebula edge 50. effectively 1/10 of full nebula. 4 deg field. 

7/18/23

RASA - QHY183 2asecs pixel size, nominal resolution 4 asecs. 

Hot evening in Austin (Friendship Observatory), seeing poor 2/5 = >4asecs. Exposure  150 sec with narrow filter. Tracking at 1 asecs RMS (2 asecs FWHM).  Measured resolution 10asecs unaffected by tracking. Need better focus process.... key on bright star. Background light 6/255 for 150s @G30 (ISO3200)

https://www.cleardarksky.com/c/FrdSpObTXkey.html

Use  a pin point light source with PhD2 on QHY183 for focus/collimation check. 

BATTERY EXTENDER

https://www.bhphotovideo.com/c/product/1235872-REG/tether_tools_crups110_case_relay_camera_power.html. Use existing battery with USB source. 

PROCESS FOR DEEP SKY 

Parts list 

Tripod - counter weight - Handboard

Telescope (includes RASA cables)  - SCT - RASA - QHY - Svbony - Sony a7s - spare Sony battery. 

Dew shield - Dark bag

Small battery - large battery -  1 power/concentric/Lighter - I  power/AC

T2/SonyE - T2/Svbony

2x USBC - USB for Svbony & QHY SCT

USB hub &  phone cable for tracking.

iPhone 10 for finding polestar.

iPad for Skyguide navigation. 

Configurations

Stage align - 2 star - laser pointer w/wo 400mm / Sony a7s.

Targeting - 400mm / Sony a7s for wide field view  -  SCT / QHY USB to Laptop.

Tracking - 400mm / Svbony  USB to Laptop via Hub. Phone connection Svbony to Tripod OR USB/USB mini for Laptop to Tripod Handboard (need to test).

20mm Viltrox lens assembly 

2 segments; one includes nose with aperture, and the other includes  focus with spring between. When dropped, the screws in nose pulled out. Reassembled by gluing the nose screws to the holes in the focus assembly. 

Focus assembly disassembled by removing 4 screws in E mount ring. Undo ring holding focus lenses - DO NOT invert. Unscrew 3 screws to release focus assembly body from shell. Re-attach focus lens ring. The focus assembly can now be unthreaded from the focus shell. 

 

If the focus lenses fall out they need to be reloaded in the correct order as in the drawing. Nose doublet first, step up ring, converging lens, gap ring, first thin asymmetric  diverging lens low curvature side down, second thick symmetric diverging lens. Be sure to check image quality, if edges are poor, reverse the first thin asymmetric diverging lens. Reattach focus lens ring until if and when the focus body is re-attached to focus shell. 

Threads

https://agenaastro.com/articles/guides/astronomy-threads-explained.html

T2 = M42 0.75, Pentax = M42 1.0.

Solar

Lunt Solar 50mm Ha Solar Telescope with Pressure Tuner / B400 Filter # LS50THa/B400PT  $950

  • Type: Single Interference Etalon

  • Tuning: Internal Pressure Tune (Doppler True Tuning)

  • Aperture: 50mm

  • Focal Length: 350mm

  • F Ratio: F/7

  • Bandpass: <0.75 Angstroms @ 656 nm

  • Focuser: 1.25" Helical Focuser

  • Mounting: Integrated clamshell style with 1/4-20 tapped base (Vixen dovetail rail available separately)

Solar HSO images

Dark spots surrounding by lighter tracks. Need 20% of 200 images to get detail, easy to overexpose and loose detail in center of sun 20msec G10 was overexposed. Edge regions seem to show more texture. Need to match brightness at sun center to match images. HSO image had a blue center, OSH had a orange center.

The Sun is a black body emitter peaking at 500nm, and is white over the visible range. The elements in the sun appear as absorption lines. Therefore H rich areas appear dark, or blue in a RGB image.  In an HSO image, the S & O wavelengths are filled by blackbody emissions. 

 - suggests HSO or HOO as palette. The texture in the sun are caused by variations in gas density  blackbody emissions AND  H content. Prominences are hydrogen emissions and are therefore the compliment of the H absorptions in the surface of the sun.  

Lens Measurements 

Using the artificial star. 

Nikon P100 at 100mm, 5 pixel or 5 um at the image plane.

100mm Canon/ QHY 3 pix center 5 pix edge @2.4um pix-1 = 10 um center17 um edge, measured using HFD from PhD2 programRequires a focal plane glass for focus.

Full frame lens so 10um in 35 mm is 0.5ppm correction. 

100mm Sony / a7s 3 pix center @ 8um pix-1 = 24 um center or 0.8ppm. 14 and 20 mm with Sony a7s 3 pix. probably pixel limited. NO focal plane glass. 

iPhone 14  - 1x lens looks like 7--8 pic FWHM, or 8-10um at the image plane, comparable to 35 mm lens. 

Aperture vs. f number 

Star size 50um. 

Distance = Spot size * fl / pixel 

For 100 mm fl lens, 400mm focal length 4x larger.

Sony a7s 8 um pixel. 

20mm/Sony 7as crossover 1.2m  f2.5 & 6.5 & 22 

100mm / Sony a7s crossover 0.6 m use f2.6 & 6.5 & 22 down to 0.3m. 

400mm/ Sony 7as crossover 2.5m. f6.5 &22 down to 5 m. 

Distance series. Baseline settings at the brightest as in the closest focus position, just below saturation. 2x increments in distance. Then change lens. 

Plot Intensity vs pixel/star ratio; >1 aperture limited, <1 f number limited. 

For Milky Way and distant galaxy nebula a pixel sized emitter need to be f number limited - high f.   Use C6 RASA for any colorful object including Stephan's Quintet. 

For galaxies a collection of point sources need to be aperture limited, low f number keeps background low. Use C6 SCT - or larger if available. Test on C6 then try C14.  This is why v. large mirror systems so effective for distant galaxies. 

RosetteNebLayers32HOO Final Small.jpg
OrionHOS2Small.jpg
victorix20mmf1.8manual.jpg
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