M42

Good evening. If possible, I have a question. Tell me, a guide scope like yours, with a 200 mm focal length—is that sufficient for guiding with good accuracy? I have a small 70 mm refractor with a 400 mm focal length, and I was thinking of using it as a guide scope. Or is that too large?

Feb 24th, 2025

mikeReply to scuttum

My guide scope works fine for me. But you also need to consider the pixel size of the guide camera and the ratio of the guide scope’s field of view to the telescope’s. I think 400mm will be quite good. However, the focal ratio of your guide scope—400/70—will be a bit too slow. You might run into issues finding a suitable guide star.

Feb 25th, 2025

scuttumReply to mike

Well, yes, 1/5.7 is twice as dark as 1/4. I'll give it a try. So, I dug through my spare parts—there's also a Jupiter-21 lens, F=210 mm. It seemed a bit small to me somehow. Alright, thanks for paying attention to my question! :)

Feb 25th, 2025

mikeReply to scuttum

I bought a Chinese-made lens with D=60mm/F=200mm. I printed the tube on a 3D printer.

Feb 25th, 2025