HOW IT's DONE - IMPLEMENTATION
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.
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
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 1.2 4000 12 16M 6 EX 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 1500 12 2M 6 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 IMX586 0.8 8000 10 48M 8 EX-R stacked 2022/2018
Canon E mount 44mm
Pentax M42 45mm
(1) EX = Exmor. EX-R = Exmor - R. Exmor R is a back-illuminated version of Sony's CMOS image sensor. Exmor R was announced by Sony on 11 June 2008. Sony has newly developed a unique photo-diode structure and 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 6x improvement.
(2) Noise at around ISO3200 20sec exposure. G30 on QHY = 3200 ISO.
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.
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.
Svbony Capture in SharpCap .FITS preferable to NINA.
Gain in Sharp cap is 10x NINA Gain 300 = ISO 3200.
QHY 183 cooled - 10 bit noise FWHM on 120 sec exposure so 1024 gray scale levels.
QHY 183 NINA Gain10 = ISO3200 Gain30 = ISO32,000 Gain50 = ISO160K
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)
Pro QHY cameras come with optical fiber connection, and optical frame grabber card in PC for real time video.
Use S7as back on C6 RASA if you want large f number telescope.
Use subsample for focusing.
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.
Save as RAW16 FITS format.
PIPP -Debayer in 2 places YES , White balance YES BGGR pattern Output Split RGB NO - confirmed correct color balance
PPG seems better.
Stack in Autostakkert COO align
PS 3x resample.
Topaz OOF V blurry
Stack in DSS with FITS specified in load. Output as TIFF and you get full color image.
30 sec Dark has 4(8bit) FWHM noise - comparable to QHY which makes sense.
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 + 2mm T2 tube
Sbony 305 + Adaptors = 20.5mm does not work
Orion ED80 configurations
400mm focal length 80mm aperture f6 lens 1.2 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.
400mm- focus 2cm + Field F + T2 to NEX + Sony7as Camera limited resolution 400mm RGB 3.5 asecs/pix unusable undersample
400mm- focus 5.2cm + Field F + 38mmT2 + Svb Diffraction/pixel match 400mm RGB 1.1 asecs/pix undersample
400mm- focus 5.2cm + Field F + Filter wheel + QHY First line filter images 400mm HSL 1.1 asecs/pix
400mm-focus 4cm + 2.5" to 1.5" + 1.5" to 5x + T2 to NEX + Sony7as 2000mm RGB 0.8 asecs/pix undersample
400mm-focus 1cm + 2.5" to 1.5" + 1.5" to 5x +38mm T2 + Svb 2000mm RGB 0.25 asecs/pix adequate sampling
400mm-focus 1cm + 2.5" to 1.5" + 1.5" to 5x +85mm T2 + Svb (10x mag) 4000mm RGB 0.12 asecs/pix good sampling
Celestron 6 configurations
To check collimation, place star in middle of field using eyepiece. Defocus and obstruction should be symmetric in the defocus ring.
Move finger shadow to find mirror screw closest to narrowest ring, if in between use opposite screw
Move star to edge of field in direction of narrowest ring.
Adjust screw 1/6 of a turn to move star back to center of field.
If to loose, tighten other two screws, if too tight loosen the other 2.
Prime focus imaging C6 0.7 asecs resolution
C6 + C6 to T2 converter + T2 to Sony E + Sony7as 1500mm RGB f10 1.0 asecs/pix 0.7x sample
C6 + C6 to T2 converter + 38mm T2 tube + QHY 1500mm HSO f10 0.35 asecs/pix 2x sample
C6 + C6 to T2 converter + T2 to C +Svbony 1500mm RGB f10 0.35 asecs/pix
C6 to 1.25" converter + 1.25 to eyepiece + eyepiece 5x T2 + T2 to Sony E +Sony 7as 7500mm RGB 0.2 asecs/pix 3.5x adequate sampling
C6 to 1.25" converter + 1.25 to eyepiece + eyepiece 5x T2 + T2 to C +Svbony 7500mm RGB 0.07asecs/pix 2amin field 10x good sampling
RASA C6 with Hyperstar 6 V4 with filter 3 asecs resolution Bf 39.8mm M42
C6 + Hyperstar M42 + M42 to T2 + QHY 300mm HSO f2 1.7 asecs/pix 3 degree field X
C6 + Hyperstar M42 + M42 to C +Svbony 300mm RGB f2 1.7 asecs/pix 1 degree fieldX
Hyper star back focus 39.8mm.
Filter drawer thickness = 17.5mm need a 5 mm ring with QHY 183.
SCT matches refractive for MTF< 0.25.
At the traditional resolution of MTF = 0.5, resolution reduced 2x.
Low noise - high bit count imaging helps to recover the lost contrast.
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.
With QHY 183 camera C6 RASA has 1.7 asecs/pix under-sampled, C14 RASA 0.6 asecs/pix optimal sampling.
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.
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 HDR or FWHM = spot size in pixels.
For RASA & QHY pixel 1934 pixels = 44 arcmins, 1.6 arcsecs/pix.
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"
Comparison C11 Hyperstar 4.2 arcsecs FWHM, Edge 3.5 arcsecs FWHM. Very similar - probably seeing limited.
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, 2.4 pix FWHM. FWHM is roughly +-90% of a single edge.
10/25/22 First test Elephants Trunk - min star 6x6 pixels = 10x10 arcsecs coned 90% FW - needs collimation FWHM = 5.8 pixels = 9.9 arcsecs. Autoguide 4.24 asecs HFR RA = .85 sigma, DEC 0.4 sigma.
Resolution test: 7 arcsecs FWHM = 1/2 pitch is 50% MTF =(Imax-Imin)/(Imax+Imin)/ MTF(0) . Definite astigmatism.
asecs vert horiz.
3 10% 7%
11/3/22 First Bakinov collimation min star 3x3 pixels 6x6 arcsecs = FWHM 3.7 pixels. @1.7 asecs/pix = 6.3 asecs.
Better, not good enough. Reset Hyperstar. Guide camera 400mm HFR = 2 asecs RA = 0.5 sigma.
Before any touch of the telescope, turn tracking off, after re-select star.
Resolution target - Use MTF and fine l/s contrast to quantitatively optimize collimation with minimal atmospherics. At 25 meters, 2 asecs l/s (FWHM) will test C6 RASA, not usable for C6 SCT at 0.4 asecs FWHM. Could use 2 mirrors to lengthen baseline to 75m. Alternatively, use edges with the water tower wire at 1 asecs. Need to find 2 medium sized mirrors.
11/16/22 I set the Hyperstar with a 0.015" or 0.4mm gap. MTF 0.5 @ 11 asecs FWHM.
11/27/22 set the Hyperstar at zero. Make 1/2 turn on each axis to see which has an effect. 1/4 turn is too much.
11/28/22 At zero MTF 0.5 @ 5 asecs FWHM - pixellation limited. MTF 0.3 @ 4 asecs = HFR = 3 which is target. adjust does not improve.
7/21/23 Adjust tilt, a star has around 2 pixel FWHM = 4 asecs.
8/16/23 Hyperstar 10 asecs l/s = 0.5MTF, 5 asecs 0.25MTF. For Nikon P1000= 0.72MTF, 5 asecsl/s for 0.5 MTF. Poorer than 11/28/22 test so is Nikon P1000. but 2x better than Nikon P1000 which is what is should. Poorer performance from both probably because of thermal distortion,
Imaging star in warm air seeing 1.6asecs/pix, 6x6 asec min starsize. Aggressive brightening sees the base of point spread.
QHY Interface M42/0.75, 4.8mm (3/16) to Filter slider M42 - 2 asecs/pix camera res - 1 asecs/pix image res -
Test artificial star- Use LED torch with 1mm hole drilled in black plastic mask. Place at 20m = 10 asecs. Expose Gain5 & 0.0001s to get grey scale image.
Test resolution target - "5" = 8 asecs pitch, 4 asecs l/s.= FWHM
Before you mount the HyperStar, use shims to set a nominal “zero position.” Select shims in the thickness range of 0.030” – 0.040”. Loosen the tilt adjustment screws, insert three identical shims and re-‐secure the adjustment screws to create a uniform gap determined by the shim thickness. (See Figure 4.) When you are done, make sure that all of the push-‐pull tilt adjustments are secured and remove the shims.
Or 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
Best results so far in default position.
MTF measured using resolution test pattern at 25 meters.
MTF = 0.5 FWHM
Pattern 5.0 = 8 arcsecs pitch, 4 arcsecs FWHM.
Nikon P1000 12,000mm =1.2asecs, MTF = 0.5 0.8 asecs diff limit.
3,000mm =1.4asecs, MTF = 0.5 @ 0.6asecs/pix
100mm = 60asecs, MTF = 0.6
Svbony 305 400mm FWHM = 4asecs, based on autoguide HFR @1.6 6asecs/pix
Svbony 305 480mm 5x FWHM = 2.0 asecs based on MTF with 5x essential.
Edge FWHM = 2x 75-25%
FWHM asecs asecs/pix
C6 RASA 10.2 1.7 collimation limited = FWHM 9asecs
C6/5x/Sony 7as 4 1 digitization limited = 2 pixels per edge
C6/5x/QHY 1.1 0.12 should be 2 x better, probably limited by mirror collimation.
Nikon P1000 1.2 0.12 0.8 asecs diffraction limited
ED80 5x 1.8 0.22
Test 5x on Orion with Svbony camera, Nikon, C6 RASA.
Svbony - 5x is essential to avoid digitiation artifacts.
Nikon has better MTF but jpeg artifiacts compared to ED 80.
NINA does better debayer than Sharpcap. Sharpcap has better tools. Ezcap only works with QHY low brightness.
Celestron NEXIMAGE 10 SOLAR SYSTEM COLOR IMAGER $309.95 1.67um pixel Item #: 93708
Existence proof that C6/2x/ASI 3.75um pixel looks good, almost identical. 2x would give better digitization.
Good choice for planets, if 5x causes abbertions .
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.
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.
Jupiter 40 asecs, red spot 3 asecs diameter.
Saturn main gap 0.5 asecs, outer 0.12 asecs.
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, (0.8^2+0.4^2)^0.5 = 1.0 FWHM based on blur of C14, diff limit 0.4 asecs FWHM,
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 0.16 asecs FWHM. 4 pixel radius blur = 0.8 FWHM matches C6.
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
C8 RASA specification 400mm focal length, spot size 4.6 um RMS = 1 sigma, or FWHM 4.7 asecs. - HFR = 2.7 pix.
C11 RASA specification 620mm focal length, FWHM 3.0 arcsecs.
C9.25 - Hyperstar FWHM = 5.4 asecs.
C11 Hyperstar 4.2 arcsecs FWHM, Edge 3.5 arcsecs FWHM.
C14 Hyperstar 3.9 arcsecs FWHM,
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.
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 55mm 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 55mm QHY/Svb (1.2) 0.4 0.6 1.7x sample observable pixelation
1500mm 150mm f10 C6 T2 55mm 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 0.12 Target set up for planets.
C14 350mm 0.4 0.16
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.
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.
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.
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.
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
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!
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.
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.
Celestron C6 SCT / 5x / Sony7as
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.
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
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 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
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.
Arcturus in Bootes
Spica in Virgo
Regulus in Leo
Vega in Lys
Altair in Aquarius
Arcturus in Bootes
Altair in Aquarius
Capella in Auriga
Stephans quintet in Andromeda
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.
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.
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
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.
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.
100 mm lens - QHY as finder/guider 11 degrees, 7 asecs/pix.
Polemaster as a finder 11 degree field - 30 asecs res.
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
Error after linear = 0.45 asecs - measures seeing and detection effects
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.
HSO filter image
Filter changer -
30s crude align
120s needs fine align.
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.
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.
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)
Use a pin point light source with PhD2 on QHY183 for focus/collimation check.
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
Imaging - Celestron C6 with Hyperstar, filter drawer, QHC 183 mono camera, cable dress.
LED align projector - Test align with image in day light.
Tracking - Pentax 400mm, color camera - Test align with Imaging
USB bus for tracking and control
USB single for imaging
Small battery for tripod drive
Big battery for camera cooler
1) Power tripod
2) Polar align
3) Use keypad to do tripod align, eyeball align of LED to target star, use 2 star. Find 2 bright NGC stars in same sector as targets
4) Move to target using NGC number.
5) load filter, focus, adjust expose to get background around 70-80.
5) Launch tracker, select track star, calibrate, expose using ??? program 10 cycles. stop track.
6) Change filter, refocus depending on filter, adjust expose, select track star, no calibrate, expose.
Focus program - settings
Track program - settings
Expose program - settings