Tracking for Lunar

[andyrawlins]

Hi All, I'm looking for some advice about how to keep my subject in frame when imaging the moon.

I'm using a 1200mm f6 Newtonian on a HEQ5 Rowan with a 3x Televue Barlow, so 3600mm focal length ,and an ASI 224MC camera.  I am polar aligning with an iPolar which does seem to have issues with camera centering so I re-align when I'm at my target so polar alignment should be good. When imaging at this focal length with an IR pass filter, which gives the best results, I'm only getting 25fps so to get 15000 frames takes 10 minutes.   

The problem is, in this time, the image shifts and I lose some of the things I want to image.   The stacking takes care of this but I do lose some of my image, or at least the quality of the area at the edges of the image (I stack with ASI Studio which I find the best but I'm not sure how it deals with a shifting image) .

I can't use guiding as far as I know as obviously the moon is moving faster than the stars.  I can, and do, manually re-center the image during capture but this isn't ideal for several reasons.

So my questions: I

s some drift to be expected with this mount/focal length or do I have a problem with the mount?

If drift is to be expected, what do i do about it?  Obviously I can lower the focal length or just crop the image but that isn't fixing things, its just putting up with them.  I'd be grateful to hear what others are doing.

Cheers

Andy

 

 

Edited April 30, 2023 by andyrawlins
to improve it

[woldsman]

The Moon moves in DEC as well as RA with a varying orbital speed. Unless you can get guiding to work on a Lunar feature, I think you would have to make manual adjustments with a video capture as long as 10 minutes at that focal length. 

[andyrawlins]

I eventually solved this.  It was Third Axis balancing.  I came across this by chance - I had never heard of it before which amazes me because its so fundamental.  Maybe for a small refractor its fine but for a biggish Newtonian  stretching the mount towards its limit it makes a huge difference.  All I needed to do was rotate the tube so that the centre of gravity was in line with the axis of the mount (rather than having say all the weight of the focuser, finder etc on one side) and all of a sudden it tracks very well and also finds targets much better.  

Its difficult to describe in words but there are some great videos out there explaining the issue and how to solve it.  If I can re-find the one that solved this for me I'll  post the link.