75-300mm focus problem

[Atreta]

Good news, clouds broke free for a few hours today and i could give the lens some more tests. I used APT liveview again to focus on the moon as bests as i could and took a few single shots and also captured the liveview feed. After the moon i went for the eta carina nebula to check if focus was indeed good and also to see if i could get rid of the weird star shapes.

This is a crop of one the moon single shots.

Bellow is the stars tests, i had to stop the lens down to f8 to get good star shapes, from f5.6 up to f7.1 it was showing a lot of chromatic aberration and weird shapes.

The focus issue seems to be solved, but i still think the lens is not performing as it should.

This one is a single 30s  iso 800 picture at f5.6, very noisy because of sensor temperature ( 40c ):

 

 

This last one is at f8, star shapes look much better, but there is a lot of coma around the corners:

 

[Buzzard75]

I see the coma you're talking about. I had it in my Orion and Rosette Nebula pictures as well. Once you get multiple exposures and stack them it will help clean it up a bit as well and sharpen your stars. It won't be perfect, but it will be better. You'll crop the worst of it out anyway. Based on the coloration, I assume you're using some sort of light pollution filter. Using some calibration frames will fix that too. Can't wait to see the final product as Eta Carina isn't visible from here.

[Atreta]

Thanks, Buzzard75,

The purplish color i believe is chromatic aberration. I have yet to buy a LP filter, it's hard to find astronomy stuff in stores in here. 

As for the eta carina nebula i have about 8 hours of images taken with the 135mm lens, I'll post after i process it. It's a beautiful nebula.

[Buzzard75]

I guess I never realized quite how purple my RAW files looked. Deep Sky Stacker really cleared them up better than I thought it would. Hopefully stacking will fix a lot of that for you too.