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Astro imaging 

The challenge in astro photography is the wide range of objects, and dealing with all the astronomical and weather cycles. The planets are the smallest  (10's arc secs)  and brightest objects, the Milky Way  is the largest diffuse object covering 25% of the night sky with many colorful nebula, and the galaxies are the most distant objects from Andromeda at 3 degrees in size out to the most distant only visible in the Hubble deep field. Imaging dim objects require dark skies during the new moon and good cloudless weather. Spatial resolution is dominated by atmospheric distortion or seeing at around 1 arcsecs so 10 arcsecs is the smallest imageable object by terrestrial amateurs. Seeing is improved by cold nights, no wind, and high altitude. Outside of the atmosphere, Hubble can resolve 0.05 arc secs.

The size range of objects require both telephoto and wide angle lenses.  Telephotos have focal lengths much greater than the sensor, with narrow angular fields and less lens curvature. The resolution is typically diffraction limited depending only on the input aperture. My 480 mm telephoto and "3000 mm" lens in the Nikon P1000 both appear to be diffraction limited at Rayleigh = 1.7 arcsecs with an acceptance angle of 6 degrees or less. The Milky Way requires wider angle lenses that have focal lengths similar to or smaller than  the field size which requires more lens curvature, and has a  resolution that is aberration limited and is typically between 50 and 100 line pairs per mm. at the sensor.   A resolution of 100 lp/mm requires a pixel size of 2.5 um typically available in 1/2 field (15mm)  sensors.  My 100 mm focal length lens with a 20 degree acceptance angle has a resolution of around 15 arcsecs, much larger than the diffraction limit of 2.2 arcsecs, and so is aberration limited. For comparison 100 lp/mm is 200 ppm, whereas a state of the art semiconductor lens will resolve 10 ppm. 

The aperture of a telephoto lens determines how much light can be captured and hence the dimmest point source star that can be imaged.  The focal  length combined with the size of the image sensor determines the angular field size, and with the pixel count of the sensor, determines the angular resolution per pixel. The Rayleigh limit is the smallest resolvable distance between 2 point sources, i.e. 2 1/2 lines and 1 space.  There needs to be at least 2 pixels inside the Rayleigh resolution limit, preferably 4. Finally, the ratio of aperture to focal length or "f number" determines the ability to capture diffuse objects such as nebula. F number is critical because it determines the exposure time and is widely available in lenses up to 100mm focal length. The Celestron SCT reflector telescopes can be set up with camera at the  main mirror focus (RASA configuration) as a f2 lens with focal length around 400mm and resolution of 2 arcsecs, perfect for Nebula and galaxies.


The brightness of astronomical objects vary's from the Sun to distant galaxies.  A typical exposure of the moon is 1/400 at ISO 200 using a f6 lens that looses 10x light compared to f2. The relative intensity of the moon measured by the camera = f number multiple / exposure time / ISO = 20 sec-1 ISO-1. The short exposure time means that a large number of images can be collected, and the best 10% selected for "lucky imaging" that minimizes seeing distortion. RAW images need to be collected rather than compressed video.  The benchmark exposure for the Milky Way that shows details of nebula with a f2 lens is 20 sec at ISO 2000 = 2 E-5 sec-1 ISO-1. This is consistent with  Magnitudes, the difference in intensity between the moon (M9) and nebula (M-5) is  5E-6.

The earths rotates  at 15 arcsecs/sec, so a wide angle 20 mm lens and Sony 7a camera  that has at least 100 arc secs per pixel will just allow an untracked exposure for 20 secs. A 100mm lens and Sony 7a camera at 20 arcsec/pix just works at 5 sec exposure ISO 8,000.   A 400 mm telephoto lens and QHY camera at 1 arc secs per pixel, has a maximum untracked exposure time of 1/10 sec ISO 100K . 

Long exposure times  and/or small imaging fields require tracking the camera to offset the earths rotation.  Equatorial (RA) scanning stages sit on a 2 axis rotation (Azimuth) and tilt (Altitude) stage to align the RA axis with the earths rotation axis.  Alignment of the stage axis to the earths rotation axis is critical. The Polemaster align camera has a pixel resolution of 30 arcsecs, and a field of 10 degrees.  Crude visual alignment that puts the polestar near the center of the Polemaster field gets to 1 degree of the earths axis. Rough align to within 4 arc mins produces a measured drift of 0.1 arc sec/sec.  "Perfect" alignment to the earths axis to within a Polemaster  pixel (30 arcsecs)  gets to  0.01 arcsecs/sec, equivalent to 100 sec exposure for 1 arc secs resolution.  It is important to do the align multiple times so as obtain the best align. Most of the error is in Altitude, which can be optimized by looking for drift with the camera pointed to East or West.

There are 2 styles of scanning stage; German equatorial, and dedicated RA.  The German equatorial stage has 2 motorized perpendicular rotational axes, RA and DEC to find the feature of interest, the RA axis also follows the earths rotation. To achieve 1 arcsecs of error in 360 rotation axis requires 1 ppm of positioning  which in turn requires a reduction worm gear. Due to machining limitations, a $1000 stage such as AVX has an accuracy of +- 20 arc secs across a full worm cycle of 8 mins. A short exposure of 30 sec (6% of the cycle) has errors as small as 1 arcsecs.  A $5000 stage such a Fornax EQ mount has a full cycle error of  +- 6 arc secs. Periodic Error Correction over the worm cycle can halve the error.  The addition of a high accuracy encoder (Telescope Drive Master) can achieve +- 1-2 arc secs.  


The most common solution is using a guide telescope. Guiding programs such as PHD2 have sub pixel (0.3-0.1 pixel)  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. Performance as good as 0.5 arc secs have been reported. 

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. 

Image capture has been revolutionized by digital imaging, and has opened astrophotography to amateurs. The problem is of course that the interesting features are very dim. Displays have an intensity resolution of 8 bits producing good looking images with 256 levels. In 2022, digital cameras have 12 to 16  bits A/D resolution. A 12 bit image has 2^12  =  4096 levels  stored in 16 bit RAW format images.  As a result, 16 display levels for 12 bit, 4 levels for 14 bit, 1 level for 16 bit,  contain 256 levels  in  RAW data, and can be expanded to create excellent images with 1/10 to 1/200 of the light of a traditional 8 bit image. To use only 16 display levels, the background noise must be around 1 display level to achieve a SN >10.  The noise in the image, vary's with sensor type, and  ISO. Large pixel area sensors as used in Sony 7as have better low noise performance.  A 30 sec exposure on the 7as  automatically includes dark subtraction and has a noise FWHM <1 at ISO 2000. An 10x increase in ISO to 20,000 increases noise FWHM to 13 out of 255, which can be reduced by the square root of the number of frames averaged - suggesting that  100 images are required.  A cooled CMOS camera has much lower noise, at an ISO 3200 (Gain 30), a 90 sec exposure has FWHM <1 without dark subtraction. However, most CMOS imagers do have systematic amplifier noise that still requires dark subtraction.  After averaging multiple images, further reducing noise using Topaz AI noise reduction is an effective first step in image processing before stretching the intensity levels.  The practical limit on exposure time is the background light level that depends on the Bortle level of the location, a practical target is around 50 display levels.

Line filters for HOS lines support imaging in high Bortle locations, and much higher color contrast. The filter plus holder are around 30 mm thick, so lenses require at least that distance from lens flange to camera flange ("back focus distance"). Telephoto lenses (400mm refractor and 1500mm reflector in both SCT and RASA configurations typically have large back focus. Short focal length large f number lenses  (100mm and 8 mm) for mirror DSLR  have 44mm back focus that can be used in a Canon EF mount to T2 adaptor that includes a filter drawer.




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 or ASI), will give  50-75 degree field of view and enchanced color contrast Milky Way. 

Milky way with foreground looking away from moon. Full moon rises in east at dusk, sets in west at dawn. Waxing -increasing- moon sets in west around midnight.  Waning - decreasing - moon rises in east at dawn. 


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 1/20 compared to RGB filters that have a 150 nm bandwidth. Essential to use f2 lens combined 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. 


An f2 lens using  70x20secs @ 6400ISO or equivalent good for Andromeda, 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. 

3 choices:

1) Use reduced field "100mm" Canon with QHY RGB limited to 15 arcsecs  resolution. 

2) RASA set up SCT lens  (Celestron C6 + Hyperstar) with QHY RGB with 3 arcsecs pixel resolution. Noise FWHM < 1 

3) f6 (1/10x) telephoto 10x30secs / 25,600 ISO with Sony 7as  with 5 arcsecs resolution and 4 FWHM noise.


The planets are much higher brightness and much smaller (20-40) arcsecs, so resolution is the key requirement. Seeing limits effective resolution, can be as low as 0.4 arcsecs. "Lucky imaging" is critical. Need at least 100 best images to stack. 


3 Choices:

1) Nikon P1000 super zoom "3000 mm" nominal with 4x digital zoom to get to "12,000 mm",  at the chip it is 1.2 arcsecs/pixel and after sampling 0.3 arcsecs/pixel.  Lens Rayleigh resolution 1 arcsecs.  2160i video allows 20 fps sampling for maximum lucky imaging. 

2) 400 mm refractor with 5x converter and 2x extender to get to "4000 mm" with Sony 7as produces 0.6 arcsecs/pixel  resolution or 0.3 arcsecs/pixel  with smaller sensor. Lens Rayleigh resolution 1 arcsec. Store multiple full images to stack at 1 fps. 

3) Use 1500 mm SCT reflector extends to "15,000 mm" with 5x converter and 2x extender. Lens Rayleigh resolution 0.7 arcsecs. Sony 7as produces 0.2 arc secs/pixel resolution. 

Resolution Summary:

                                                                        Color                                                              Line filter

Lens              Field Degrees       Pixel(Res)    Camera        Field Degrees          Pixel(Res) Camera

                                                       asecs                                                                  asecs

100 mm          f2             21                (20)          7as                            10                     15          QHY 

300 mm         f2                2              2 (2 )          ASI                              3                        2           QHY      

480  mm         f6               6              5 (8)           7as                             3                     1.4           QHY 

480x5 mm    f20             1.4             1                7as   

480x10 mm  f50                                                                                                         0.14 (0.8)   QHY                                                                       

1500 mm      f10             0.6          0.7 (1)           ASI                                                                            

1500x5 mm  f20             0.1         0.14(0.4)       ASI 

Measured resolution of Orion ED 80 -400 mm lens 0.8 arc secs edge resolution 0.14 pixel resolution, 1/2 Rayleigh resolution of 1.7 arc secs. 

Sony effective pixel resolution is 1.5 x actual due to RGB color pixels.

Lens selections  

Planets 5000 mm effective focal length,  0.14 asecs/pix.  Orion ED 80 = 0.8 asecs res.  Celestron 150mm = 0.4 asecs res. ASI camera. 

Large nebula 100mm f2 line filter QHY, 20 asecs res, > 1 degree in width. 

Small nebula 300mm f2 line filter QHY, 2 asecs res. 

Deep Sky galaxies: Orion  480mm f6, Sony = 8 asecs res, QHY/ASI = 3 asecs res. Celestron 1500 mm f10, QHY/ASI = 1 asecs res.

Milky Way 20mm f2 Sony.

Brightness =  Lens  block  *  Filter block / ISO / exposure time

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

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

Cooled camera reduces noise  2x

Filter exposure times need to be G30 240 secs (4 mins) 

f2 telescope should work well with filters in Austin.

G30 on QHY = 3500 ISO.

Focuser for Orion ED 80  CT - telescope has 2.5" ID and 2 7/8 OD interface. 2.5" focuser needs a 2 7/8 (73mm) ID adaptor with outside screws. 


TS-Optics 2" V-Power Crayford Focuser for Refractors, Cassegrains, RC, ...  $269 inc. shipping.


GSO with adaptors

Explore Scientific

Align Stars - bright and directly above 

Polaris in all seasons 


Arcturus in  Bootes

Spica  in Virgo 

Regulus in Leo 


Vega in Lys

Altair in Aquarius


Antares in Libra 


Altair in Aquarius


Capella in Auriga 


Sirius in Canis Major 

Capella in Auriga

Rigel in Orion

Procyon in Canis Minor

Pollox in Gemini

Betelgeuse in Orion

Aldebran in Taurus


Saturn and Jupiter grand conjunction (one day before)

Camera is a Nikon P1000 on a Fornax tracking stage so the planet stays in frame. Get the zoom setting right at 6000 mm equivalent. Take 1 min videos at different ISO settings for the moons and planets. Wait for the perfect align to get a single align shot. Wait for planets to move away. Go back and get a video of the right bit of foreground. Use software to separate into frames and then stack 100+ frames to a single low noise image at each ISO using AutoStakkert. Then assemble the images in Photoshop. Using the align image as background image in the layers, cut around the foreground, planets and moons layers to form a spatially correct, very high dynamic range, composite. You have to size the cuts to cover up the overexposed planets in the background layer. Merge the layers and adjust to taste !! Its the better part of a day post processing to get it to work. The key really is the frame stacking it reduces the low light ISO noise and the atmospheric noise. QED!

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Andromeda (M31) Mag.  3.4, Size 3 degrees.

Above M110 Mag. 8.9, Size 21'.


Photographed using a Canon 7as

400mm f6.1 exposed 10x30 secs @ 25600 ISO at 1.5M ISOsecs, Fornax tracking stage.

Bortle 2 sky - background at Mag. 11. 



Flame Nebula in Orion Mag. 7.2, Size 30', illuminated by the neighboring star Alnitak Mag. 1.74.

Photographed using astro mod Canon 7as 400mm f6.1, exposed at 0.6M ISOsecs. Fornax tracking stage. 

3 degree field of view. 

Bortle 4 sky - background at Mag. 9

HDR created with the stars imaged by 4 smaller exposures, converted to B&W and stacked, then stacked with the nebula image. 


Stitched fish eye view panorama June, Sept and Dec, March in southern hemisphere. 

20 mm lens with a  84x61 degree field @ 20secs 2000 ISO. In landscape orientation starting  20 degrees angled up. In 4 vertical rows 25 degree increments; on the horizon 25 x 15 degree rotations, 12 x 30 degree, 4 x 90 degree, 1 vertical view. Assemble each session using PTgui software using equirectangular mode and linear corrections, discard any excess images.  Combine sessions by manual stich, and take out edge illumination artifacts using PS level in +- 10% level increments.  

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To scale, temporal shifted, composite of deep sky objects.. 

VIDEO tour script


Tour Milky Way 

Planets - Moon - Mars - Jupiter - Saturn add light year clock in bottom right from here
Plieades - Antares - Orion & Flame & Rosette  - Lagoon & Eagle    - clip all and superimpose on full pan all to give depth scale full MW 10% for Orion and lagoon.

Isolate  lagoon (may be at 400mm) and zoom in keeping full MW background fixed

Pass Lagoon and zoom in to MW, scan and exit (100 mm images) 

LMC_SMC (all deep sky from here)


Triangulum  2Mly

Bode 11 then Cigar 12

Whirlpool  23

Leo M61 32 then Sarah 36 then M65 41

Hubble  11Bly

Create foreground and background for zoom.

Select key area - inverse - copypaste new layer - select big star - enlarge 3 - copy paste to form star layer - copy star layer - select bkg - inverse - enlarge 5 - move /copy/paste in original layer to replace foregrounds. Now have foreground and background. 

Match middle ground to background, zoom in final step. Start foreground 1/3 frame early to get sense of foreground relative to background.

Deep Space look 

To create realistic deep sky images without blocking stars:

1) Copy master image - set 50% opaque - and move so that that stars pairs are distinct - set transparency 100% opaque.

2) On original - select stars using Astropanel/Astro/Hot pixel/Harder filter.

3) On filter - Create mask using magic wand - adjust tolerance  on background - Contract 1 pixel.

4) Copy filter on moved master to select local backgrounds to each star

5) Reorder layers so copied filter is added to original - Merge layers 

6) Select galaxies-feather - invert-Blur to eliminate residual variation

7)  Apply  levels by moving zero to obtain almost black background - do not overdo !

TARGETS - Whirlpool , Leo triplet 

Moon Composite 

Exposure 1/125 ISO 3200  PP7.  Continuous pics with hand controller - 40 or more frames. Lucky stack at 10%. 

Remove background - point / Tolerance 60 Feather 10 

HOS  filter image

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. 

Example Elephants Trunk Nebula M5.6   

Telescope: TEC-140 (F7)

Camera: SBIG ST-8300M

Mount: AP900 GTO

HA : 18x30 minutes (binned 1x1)

SII :18x30 minutes (binned 1x1)

OIII : 18x30 minutes (binned 1x1)

LRGB image

Useful for smaller galaxies (<1 degree) and excellent seeing using 400mm with QHY for resolution 1.4 asecs/pix. limited to 10 sec exposure time, 30 sec for moderate seeing. 

Align and stack multiple exposures in Deep Sky Stacker, set brightness at mid point. In PS, copy / paste RGB channels, adjust dark and mid point. Copy in L as new layer, change layer combine from Normal to Luminosity.

Polemaster align process

Find polestar using cell phone 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 ( 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

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.

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 Components

Align guide and Polaris finder to Telescope using local reference. 

Find Telescope to Polemaster axis offset using local ref & mark RA and DEC locations. Estimated as 1 degree right and 1 degree down (10 degree RA and 1 degree DEC  - left and down keys). Just outside ED80 + QHY field. 

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 Stars

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

1) Index

2) Polaris move to marks; 10 deg clock  RA,  1 deg right DEC. 

3) Star Above.

4) Star near target - repeat. 

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.

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 / 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.  $89.00

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 

4/25/22 First light  Polemaster pole align, Orion ED80 tracked unguided. Drift 0.04 asecs/sec.

5/3/22 Polemaster pole align Orion ED 80 - QHY. Drift test RA  @ 7.5 asecs/sec.  Self RA guiding +_ 2.5 asecs over 4 mins. DEC residual 0.02 asecs/sec = 120 arc secs align error . Good for 4 min exposure on RASA  Celestron.


1) Star find

2) Get supernova target.


1) Polemaster on and off axis test. Move axis to polestar, rotate stage to prove axis. 

2) Drift test RA @ 15 asecs/sec, Guider OFF.

3) Guider test 


1) RGBL test in Bortle 5


1) Rho 100mm/Sony

2) Lagoon 100mm/QHY line filter

Saturn stack4-Shapen-DeNoiseAI-denoise.j
Jupiter close.jpg

I have a new appreciation for the nerds at Nikon. Here is a picture of Saturn that I think provides a direct measure of the optical performance of the P1000. It was taken at 12,000 mm zoom – 3000 mm optical and 4 x digital (i.e. cropped and resampled). The image was taken as a video on a tripod with a Fornax tracking stage. The focus was set manually using the remote control. A selection of the 250 best frames in a 2 minute video were averaged using Austostakkert. The results is the image with my best focus, least atmospherics, and minimized digitization.  Atmospherics dominate so frame count and pixel count is more important than low compression.  The NikonP1000 supports higher video resolution and better pixel resolution at 12kmm zoom, than the Sony 7as.   If seeing creates 20 pixel noise in 1 frame, 100 frames  = 13 pixel noise, 2000 frames = 10 pixel noise, 4000 frames 25% = 5 pixel noise. 

The dark band (Cassini’s Division) between the 2 major rings is hinted but not resolved. The average Saturn diameter is 14.5″ to 20.1″ excluding rings, 35" for outer ring. Using a high resolution Hubble photo of Saturn, also shown, Cassini’s Division is about 0.5 arc secs wide, and the dark band between the planet and the first ring is about 5 arc secs wide.

The aperture of the P1000 is 70 mm, which translates into a Rayleigh diffraction limited resolution of 1.97 arc secs. ( Rayliegh limit (1.22 lambda/d) = 1.8 arc secs, edge resolution 0.9 arc secs, recorded at 2160i video so pixel = 0.25 arc secs, with 4x video compression.

At 3000 mm, the pixel resolution of the P1000 is 0.7 arc secs, equal to the edge resolution – as it should be !

It looks to me like the limiting resolution of the P1000 must be close to the diffraction limit of 2 arc secs based on almost resolving Cassini’s Division at 0.5 arc secs, and clearly resolving the first dark band at 5 arc secs.

BRAVO – to Nikon nerds !

BTW In 1675, Cassini in the Paris Observatory used telescopes with focal lengths up to 136 feet long to observe Saturn and its division. (




Celestron 6" in RASA configuration.  Aperture 150 mm  f2 with QHY 183 /NF  

for 3 degree field 

100 mm f2 with Sony 7as  

100mm EF/Ef-T2 Adaptor filter changer/QHY  screw focus.

35mm    f3.5  QHY183/HOS  for 55 degree field.     

35mm lens/2 mm/ZWO filter/ T2 Male to Male/ QHY


Orion 400mm Aperture 80 mm f7.5 with Sony 7as                     

400mm-2cm/Field F/T2-FE/Sony7as

400mm-5.2cm/Field F/Filter wheel/QHY


Orion 400mm Aperture 80 mm f7.5 x 5x extended with Sony 7as = 2000mm   

400mm-4cm/2.5"/1.5"/P 5x/T2-NEX/Sony7as   - used to get 2 km at moon   

400mm-1cm/2.5"/1.5"/P 5x/30mm T2/QHY  - 85mm T2 for max mag.

Celestron 6" 1,500mm Aperture 150mm, 5x gives 7500mm focal length 

Nikon P1000 12,000mm Aperture 70mm f6.3  2160i video for lucky imaging. 


20 mm f2 with Sony 7as  for 80 degree field  

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


A 1.0″ disk of  seeing for a single star  is a good one for average astronomical sites. The seeing of an urban environment is usually much worse. Good seeing nights tend to be clear, cold nights without wind gusts. Warm air rises (convection), degrading the seeing, as do wind and clouds. At the best high-altitude mountaintop observatories, the wind brings in stable air which has not previously been in contact with the ground, sometimes providing seeing as good as 0.4". Seeing disk 0.4 arcsecs in a hundredth of a sec. is regarded as "good" available at Mauna Kea. 

Seeing for best Jupiter in Nikon P1000  is 1.6" (edge resolution 0.8") requires 4000f@25% to get decent image, and matches lens performance, should see some improvement with better seeing. 


1) < 0.4"  Excellent

2)  <2

3)   >2

4)   > 4  Poor

Seeing causes dimpling in image. Fix seeing issues:   


1) Use Sharpen AI twice 1) Motion Blur V Noisy - Remove Blur 2 Suppress Noise 28  2) Out Of Focus V Blurry. 

2) PS Box blur to remove dimpling,  Sharpen AI - Motion Blur - v.blurry

3) Lucky imaging for short exposures - select best 10% of images. 

4) Resolution limit, Sharpen AI - Out of focus 


Bortle Scale 

Wimberley compared to Junction 3x higher bkg =  1 Magnitude or 2 Bortles,

Line filter 500x reduction, 6x lower bkg at same S/N = 2  Magnitudes or 4 Bortles. Increase exposure time to 240 secs.

Each unit of magnitude roughly 2.5x in brightness.  Each Bortle unit is worth roughly 1.25x in visible. 

4 Bortle units = 10 x in  background intensity = 2-3 magnitudes.


The narrow filter gains roughly 2 Bortle units. 

                         Bortle       Visible Mag     Camera Mag

Austin                5                  6                      9

Wimberley        4                  6.5                   9.75   

Enchanted R     3                  7                     10.5       Good MW core

Junction             2-3               7.25                11         Good MW edge including Nebula 

Big Bend            1                  8                     12.5

QHY 183 Calibration 

In Junction (Bortle 2),  Sony f2 20s ISO 2000 has M7.92 at 193i and a background of 40i. 

In Austin (Bortle 5), QHY f3.5 20s G30 has M7.92 at 220i and a background of 120i.

So G30 is roughly 6000 ISO. 


Angular                      Nebulas                          Galaxies                                      Planets             

width deg

10                                                                             L. Magellenic

6                                     Rho Ophicho

3                                     N American                     Andromeda

2                                    Rosette/Lagoon

1                                    Orion / Elephants T         Triangulum / Leo Trip/Bode

30'                      Flame/Eagle/Cats Paw & Eye                                                        Moon

15'                                  Helix                                  Whirlpool

6'                                     Crab

1'                                     Clown Faced

40"                                                                                                                                Jupiter

20"                                                                                                                                Saturn

10"                                                                                                                                Mars 

100 mm      50mm  f2            Resolution 15 arc secs

400 mm      80mm  f6            Resolution    3 arc secs 

400 mm    150mm  f2            Resolution    2 arc secs

1500 mm  150mm  f10          Resolution  0.8 arc secs

Mag 5 feature (Rosette Nebula)

Bortle 4 location (Wimberley) S/B = 1.2   with HOS line filters S/B = 2.5  S/N(FWHM) = 7, 14 after 4 image ave. 

Bortle 2 location (Junction)     S/B = 1.5 

Bortle 4/2  3x larger background 

Bit resolution and exposure levels.

8 bit image with 256 levels looks good, 100 levels acceptable. 

QHY 183 digitizes at 12 bit depth has 4096 levels, so 5-10 levels 8 bit  will look good. 

Mag 5 line filter @ 6400ISO 120 secs  gets full  image. 

Mag 8 line filter needs 60x more exposure for full image, 6x gets acceptable that matches Andromeda satellite M110.

Sony 7as digitizes at 14 bits in RAW or 16k levels, 64x a 8 bit image.  In theory, a 4 level 8bit can produce a usable image.




Product Code DEF-1408-802

Release Date 29/08/2014 

8.42 μm pixel 14 bit ADC


 N.American , Deneb - 100mm + 7as and NF QHY in March in Wimberley 

Megallenic Clouds - 20mm / 100mm +7as in June in Botswana

Ophicho, Lagoon - 100mm + 7as and NF QHY in July or August  in Wimberley - excited cloud complex

Horsehead, Rosette - Cent 6" + NF QHY  in  Winter '23 in Wimberley or Austin 

Elephants Trunk 35 mins close to Deneb

Eagle Nebula (Pillars of creation) 35 arc min in Core

Cats Paw 35 arc min close to Lagoon 

Trifid (close to Rosette 10 arcmins M6.3

Helix 18 arcmins M7.3  in Aquarius

Crab Nebula 6 arcmin M8.4  supernova remnant.

NGC 4647 supernova

Long term

Eskimo - Clown faced nebula   54 arcsecs  M9.1

Cats eye 38 arcsecs M8.1  in Drago


Spring Northern  Galaxies, MW low in sky 

Summer  Core, rho, Eagle N, Lagoon N

Fall Andromeda, Deneb, Elephants trunk N 

Winter Orion N.


Nebulae HOS  - large 100mm, small needs RASA

Milky Way HOS - needs 8mm and ASI

Galaxies high res - needs C6 and good seeing

Planets high res - needs C6  and good seeing


Video tour

Milky Way visible with Nebula foregrounds. 

Northern Hemisphere with Galaxy foregrounds