I bought a guidescope (70 mm aperture & 400 mm focal length) for my 10" Dob (non-tracking). I was wondering if my guidescope could also be used with my DSLR for photometry. There is, as far as I can tell, no correction for chromatic aberration. Would that be an issue and would have to get an achromatic refractor. I want to keep the photometry equipment (DSLR+small telescope+equatorial mount with either tracking or clock drive) small in both size and budget if it is within the acceptable parameters for photometry. Otherwise, I am willing to pay extra if absolutely necessary.
Link to brand of guidescope below
The "Product description" section states, somewhere towards the end:
"5)Consisting of a 70mm aperture, 400mm focal length achromatic refractor guide scope, "
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Granted though, I noticed a lot of APOs or ED when people used refractors for astrophotography, so the question remains: will a small chromatic aberration be acceptable for photometry?
Oops! I missed that part. When I was looking at Jupiter, I could see the chromatic abberation. I assumed there was no correction for it, and, I wasn't expecting any for the price. I guess if it didn't have any at all, the chromatic abberations would be even worse. Sorry but most of experience has been with reflectors.
Chromatic aberration per single color channel is not too bad. Also, achromat refractors are quite well corrected for visual range - that fits entire G channel (i.e. roughly Johnson V filter). If you don't use B and R channels, you generally should not have problems.
Not to mention that you actually may want to defocus a bit on purpose, to have signal on more pixels.