Inexpensive Guide Scope recommendation?
Posted 14 October 2021 - 03:45 PM
I'm looking at SVBONY 50mm and 60mm guidescopes and their budget SV105 camera.
Would this set up provide adequate beginner level auto guiding capability for deep sky astrophotography?
If Not... What budget option(s) would you recommend?
Posted 14 October 2021 - 03:53 PM
Off topic -- pixel size for the camera is really small. Planetary -- ok, it may cause you problems for DSO imaging (even at F/4).
If this is your guide camera -- comments stay the same.
Correcting my comment - the pixels are 3um ... bigger than I remembered.
This camera in mono can work as a guide camera. For small to mid DSO's the camera will work, but you really want plate solving working.
Edited by Mark Lovik, 14 October 2021 - 04:04 PM.
Posted 14 October 2021 - 04:25 PM
Posted 14 October 2021 - 04:56 PM
I think rather than simply focal length, it’ll depend on your image scale for both your main scope and guide scope. This factors in pixel size as well as focal length.
For my 208/860mm Newt with Fuji X-T100 (3.9um pixels), I’ve used a William Optics UniGuide 32/120mm guide scope with an ASI290MM Mini (2.9um pixels). I was happy with the results.
Currently I’m using an OAG with the same Newt for guiding as the camera attached has much smaller pixels (2.9um). The guide camera I’m using has the same pixel scale (2.9um), but binning is set to 2x2 for a guider pixel scale that’s essentially 2x of the imager. I’m also happy with these results.
One thing to note is I recently picked up another camera just to use with my PA routine so I wouldn’t have to keep swapping my guide camera between OAG and guide scope. The FOV of the main scope/camera is too narrow to use with the PA routine, but the little 32/120mm works great with 2.9um pixels.
- Benschop likes this
Posted 14 October 2021 - 05:38 PM
As for guidescope focal length, the key is the ratio between arc-seconds per pixel of the imaging camera vs arc-seconds per pixel of the guide camera.
A ratio of 1:5 is generally fine, but I can guide up to 1:7.
So the answer is dependent on the pixel size of your imaging camera and the pixel size of your guiding camera.
I recommend using the calculator linked here... enter your information, and try to keep the ratio 1:7 or less
A barlow in your guidescope can help but it makes the guidestar field smaller....
For example - with a budget guidescope/ camera
I'm presently using the QHY Mini Guidescope, 30mm aperture, 130mm focal length with a QHY5L-II-M guide camera. 3.75um pixels. 5.95"/pixel resolution.
I use an ST8300M imaging camera with 5.4um pixel size. The imaging resolution varies with focal length, as follows:
Imaging Camera resol. = 1.86 arcseconds per pixel for my ED80 (600mm), the imaging / guiding ratio is 1:3.21 (good)
Imaging Camera resol. = 0.87 arcseconds per pixel for my C8 at f6.3 (1280mm), the imaging / guiding ratio is 1:6.84.(not ideal but it works)
Imaging Camera resol. = 0.55 arcseconds per pixel for my C8 at f10 (2032mm), the imaging / guiding ratio is 1:10.68 (too high)
However, by adding a 2x barlow into the guidescope, my imaging / guiding ratio becomes 1:5.34. (good)