Personally, I prefer guiding with a separate guiding scope aside the imaging scope. With this guiding method, I can have much freedom in choosing a guiding star. However, the differential flexure between imaging scope and guiding system will be a very big issue, especially when imaging at very long focal length and very bad seeing condition. |
In the past 2 months, I am doing some experiments to see how the extreme can go. What I would say now: It is not easy to do autoguiding successfully with a separate guiding scope if photographic focal length >=800mm with some beginner-graded mounts.
Here is one of the result for your reference.
Imaging scope: Vixen VC200L (200mm F9) + 0.72x reducer
Camera and setting: Modified EOS 100D + LPS-2 @iso1600 RAW
Effective photographic focal length and ratio: 1280mm F6.4
Mount: Vixen SXP goto equatorial mount controlled by Star Book Ten
Guiding: autoguiding w/Mizar GT-68 (68mm f.l.600mm) + QHY5 + PHD
Total exposure: 4 x 360s
Processing: stacking in DSS and final touch in PS-CS2
No. of DF calibrated: 4
Air temperature: 7.5C
Air quality: Transparency = 5-6/10, seeing = 3-4/10 estimated
Better result may be achieved if applying FF calibrated. But I don't take the FF yet. S/N is not good too because of insufficient exposure time. If weather cooperates, I will do it again with more exposure and FF calibrated. Keep tuned please.