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Old 11-05-2013, 11:44 PM
TanjaC (Tanja)
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TanjaC is offline
 
Join Date: May 2012
Location: Johannesburg, South Africa
Posts: 30
Flared Stars. Not Coma/field rotation. Confused

Hi All,

I'm looking for some advice to what I can do to solve the issue I have with some flared stars across the edges with my 105mm APO

I've considered a couple of things, would appreciate it if someone can add a few more suggestions to try. The issue is that if I image different parts of the sky, things improve/worsen.
When I image south (Carina) it's at its worse. North seems to be best. East / overhead slight problems

Coma
- I have an Officina Stellare reducer / flattener fitted. Seeing that without changing camera orientation - imaging N yields round stars in the corners, and keeping same setup - immediately slewing and imaging S makes it appear like field rotation

Field rotation.
- I assume it can't be this as every image over 1,5hrs matches up identically. Although a single sub might look like field rotation, over 1,5 hrs none of the stars have actually rotated across a point. (was thinking rotation around a guide star) - I have also re-polar aligned - does not yield better results.

Chip distance / camera fitting squarely
- If one or 2 corners are off, you might think its flattener and sensor not square, but then why are my stars round in the corners when imaging N.

Balance.
- I know my balance is a little off. It's balanced horizontally in Dec (balanced in RA), but not vertically in Dec. This is the only problem I can see? But then I'm still confused to why I get round stars on the left when imaging N and not S.

Also another question, should the OTA be slightly off balance in RA to give the motors something to work against? If so which side?

Mount is perfectly level. CGem DX
Polar aligned very well.
Camera Canon 60Da
Officina Stellare HiperAPO105
Focal reducer / field flattener for Hiper APO series.
0.75x focal reduction factor (http://www.officinastellare.com/acce...php?idProd2=24)

I've included links to 2 images. Leo Triplet to the N (http://astrob.in/41593/) and Carina to the S (http://www.astrobin.com/41595/). Notice how much worse the Carina image is across the left of the field. (Looks just like field rotation) - unprocessed files.


Help appreciated. What can I try to fix this (sorting out my dec vert balancing with another counterweight too)
Thanks
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