DSLR and Star Tracker Equipment

and some notes about it

Cameras and Lenses

 Currently, I use the following gear most of the time:

  • Canon EOS 100D camera, astro-modified, and sold, replaced by:
  • Canon EOS 800D camera, astro-modified, as a main camera
  • ZWO ASI294MM Pro, ZWO 8x EFW, Baader LRGB and CMOS-optimised HSO filters, used most of time
  • Canon EOS RP, rarely used
  • Canon 5D Mark IV, sometimes, more for wide-field views
  • Canon EF 100-400mm f/4.5-5.6L IS II USM, mostly used for Deep Sky in 300-400mm
  • Canon EF 70-200mm 1:4L IS II USM, some times used for wide-field and DSO in 100-200mm, shows less quality than the above 100-400 lens
  • Canon EF 200mm f/2.8 II USM, best image quality among compared to other lenses I own

I own a few other Canon lenses, but they are not used much at the moment. Their optical quality for astrophotography is not clear to me yet.

Most of the time I use the Canon EF 100-400mm f/4.5-5.6L IS II USM. This lens has received very good review result from one of the experts in the astrophotography. I bought this lens before I got into astrophotography, and it “saved” me from buying a telescope. I strongly recommend this lens! It also delivers a very good performance in daylight.

I also did some own lens tests to see how the Canon EF 70-200 f/4.0L IS II USM performs. The Canon EF 100-400mm f/4.5-5.6L IS II USM shows far less chromatic and coma aberrations than the Canon EF 70-200 f/4.0L IS II USM lens. This applies to any f-numbers set and focal length used. Most of time I stop both lenses at least two stops. In the focal length of 200mm, Canon EF 200mm f/2.8 II USM provides an incomparably better performance, especially if stopped to f/4. I once was thinking of buying the popular Samyang 135mm F2.0 lens, but decided to go with Canon EF 200mm f/2.8 II USM, since it can be better used in daylight photography.

Star Tracker Setup

  • Sky-Watcher Adventurer Mini Astro Set
  • QHYCCD PoleMaster camera for polar alignment
  • Laser pointer for the initial orientation… well, sometimes and with very short beams
  • Cullmann Concept One 622T tripod, it is a bit too shaky though
  • A ball-head mounted on the top of Adventurer Mini

GoTo Equatorial Mount Setup

  • Sky-Watcher AZ GTI mount, dual-mode firmware ver. 3.20 running is the equatorial mode. 3.20 is an important detail, since 3.26 does not work well
  • A self-made EQMod USB adapter cable is used to connect the ASIAIR to the mount. WiFi is not used because of its instability and resulted shaky guiding
  • ZWO EAF motor focuser with a belt drive setup for DSLR lenses
  • Rollei Rock Solid Beta Mark II Carbon tripod
  • Benro GD3WH geared head as an equatorial wedge (less used meanwhile)
  • HERCULES Stronghold equatorial wedge from Astro Shop on AliExpress
  • Astronomik CLS CCD XL Canon APS-C clip-on filter
  • Astronomik UHC XL Canon RF clip-on filter
  • ZWO 30F4 Mini Guide Scope (30mm, 120mm, f/4), sold and replaced by:
  • SVBONY SV165 30mm f/4 guide scope
  • “Guidescope50” no-name guide scope from Teleskop Austria (50mm, 180mm, f/3.6). It seems to be the same as SVBONY 50mm guide scope
  • ZWO ASI120MM-S camera as a guiding camera, sold to be replaced by:
  • ZWO ASI290MM Mini camera as a guiding camera
  • iPhone or iPad with cellular for controlling ASIAIR. A “cellular” version of mobile devices is a must, since it brings integrated GPS which is needed to sync date, time and position

Power Consumption on 12V

  • 12v goes to ASIAIR Pro and distributed from there to other devices
  • ASIAIR Pro idle or, surprisingly even after a shutdown: 5W
  • adding ASI120MM-S in idle, 6W in total
  • adding EAF in idle, 6.4W in total
  • adding Canon 100D or 800D in idle, 7.5W in total
  • adding AZ GTI in idle, 8W in total
  • All of the above in a worst case: Canon is in the LiveView, the mount is tracking, the guiding is in the cycle mode, EAF is moving at the “fast” speed: 13W in total
  • COOWOO Dew Heater – 5V, USB, 1,6A, 8W
  • COOWOO Dew Heater, adjustable, 5V, USB, steps 0.6A, 0.9A, 1,3A, up to 6.5W
  • For comparison, the power consumption of a Sky-Watcher EQM-35 (borrowed from a friend): 6W in idle, 8W tracking, 16W moving at max speed

The above is power supplied from a Litionite Tanker Mini 90W powerbank. Dew heaters are on another powerbank for longer sessions.

Current ZWO ASIAIR parameters

On version 1.5.3 when used with the Sky-Watcher AZ GTI:

  • Polar Alignment: I try to get it done under 5 min and achieve less than 1′ total error.
  • Telescope Settings:
    • Guiding rate: 0.5x (default)
  • Guide Settings:
    • Calibration Step: 2000ms (default)
    • Max DEC Duration: 2000ms (default)
    • Max RA Duration: 2000ms (default)
    • Auto Restore Calibration: off
    • Dither Settings:
      • Pixels: 10 (that much is needed for DSLRs)
      • Stability: 3″
      • Settle Time: 15s
      • Interval: 1 frame
      • RA only: off
  • ZWO ASI120MM-S as guiding camera settings:
    • 3s exposure. Less makes sense only with VERY good seeing
    • try to slowly increase the gain to get enough starts, but don’t overshoot!
    • select mid-sized, mid-bright, possibly round star with sharp edges
  • Settings on the Guide Graph:
    • DEC Aggr: 100%
    • RA Aggr: 70%

The average RMS error I achive while guiding with the Sky-Watcher AZ GTI is usually around 1.5″ with the large lens, and around 0.8″ with a small lens. I get more than 2.5″ on really “bad days”. Most of problems with guiding come from bad seeing, mechanical unbalancing or instability, and wind gusts. Try to improve what you can and find settings fitting your gear best before buying new gear.

Image Scale Calculations and Guiding Ratio

I did some math of the equipment I used and post the results here for reference.

The Image Scale uses the following formula:

Image Scale = ( Pixel Size in micro-meters / Telescope Focal Length in mm ) X 206

The result is in “arc-sec” per pixel.

Imaging Cameras

Camera Pixel Size in micro-m Image Scale on 100mm Image Scale on 200mm Image Scale on 300mm Image Scale on 360 Image Scale on 400mm Image Scale on 550mm Image Scale on 1050mm Image Scale on 1625mm
Canon 100D (5196 x 3464 px) 4.29 8.8 4.4 3.37 TBD 2.2 TBD n/a n/a
Canon 800D (6026 x 4017 px) 3.70 7.6 3.8 2.61 TBD 1.9 TBD 0.73 0.47
Canon 5D Mark IV (6720 x 4480 px) 5.36 11 5.5 3.78 TBD 2.83 TBD 1.08 0.7
Canon RP (6269 x 4179) 5.73 11.8 5.9 4.06 TBD 3 TBD 1.16 0.75
ZWO ASI294MM Pro 4.63 TBD TBD TBD 2.65 TBD 1.73 0.91 0.58
ZWO ASI2600MM Pro 3.76 TBD TBD TBD TBD TBD 14.1 0.73 0.48

For comparison, the popular astrophotography camera ZWO ASI1600MM has a sensor of the size 4656×3520px and has pixels size of 3.8 micro-meter. This initially looks like less megapixels than Canon 100D with a larger pixel-size. In reality, it is totally different, since the ASI1600MM is a mono camera. When using filters, you would get the all 16 megapixels of ASI1600MM for each base color separately. In comparison, even the high-end Canon 5D Mark IV will effectively provide a far lower resolution, since all its 30 megapixels are shared by the three base colors. Well… not speaking of other advantages of specialized astrophotography cameras.

Guiding Cameras

Camera Pixel Size in micro-m Image Scale on 120mm Image Scale on 180mm
ASI120MM-S 3.75 6.4 4.3
ASI290MM Mini 2.90 5.0 3.3

The ideal situation for guiding that the image scale of the guiding camera and scope should be the same as the imaging one. In practice, the 1/3 relation brings good results as well. It is hard and expensive to follow 1:1 relation. See the article Selecting a Guide Scope and Autoguiding Camera for Astrophotography by Brian at Agena Astro Products for more details


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