I started DSO imaging about a month ago with a 70mm APO. But now I have been trying to image small DSOs with my 5" MAK Scope. It needs a lot of hard work and FOV is only 0.5 Deg. wide at best .. but it gives very sharp results and I love imaging DSOs in more depth with it.
Last night was partially cloudy so it wasn't possible to polar align the scope. So I decided to do autoguiding in Alt-Az mode just to see what Alt Az limits of MAK are. I went for Leo Triplet which was about 30 - 40 Deg Altitude, in the West.
- 30 Sec Guided Exposure - Nice and round, pinpoint stars.
- 120 Sec Guided Exposure - Overexposed stars - still rounded, with no field rotation. I was imaging in west so I thought this would be achievable.
- 300 Sec Guided Exposure - I reduced ISO to the minimum possible, to avoid overexposed stars. To my great surprise, there was still no field rotation anywhere in the image ! I investigated every corner of the image, but nothing seemed elongated at all. Every star was very well rounded.
Now, I'd give benefit of doubt to 2 mins exposures - But I cannot make sense of why 5 mins exposures would have no field rotation. Is it because of the small FOV that I'm working with ? Every thing I have read places Alt-Az limit at 20 sec - 120 sec max (with no mention of FOVs)
Does a small FOV make that much of an impact that I can more than double the exposure times, without field rotation ? I have checked my image several times since last night and I'm completely confused. I'd love to hear an explanation of this.
Thanks in advance.
Edited by Agreegator, 26 February 2021 - 08:20 PM.