Monday, October 22, 2012

Albireo photo remarks

Received excellent feedback and criticism on the Albireo photo.

Manuel: Great Shot man. Love it! Very nice glow on the stars.

Phil: Nice first image. You did what I did on my recent M13 shot, which is to over-expose the subject. To be honest, I don't know how the experts do it, but I suspect they check the first image to evaluate the exposure setting before taking more light frames. I hope you had fun taking this image, because I was quite tickled with my first image. It can become addictive. Your image shows so clearly the differences in star colours. I don't think I've ever seen Albireo with such colour contrast before. Well done!

Steve, part 1: This is pretty good. Colours are there. It's very easy to lose colours on bright stars as there very easy to overexpose on all three channels and thus turn colours white. Can you pull back the exposure a bit or are the cores of the stars basically white. The mount tracked quite well but you can see it's not perfect.  The stars are a little bit bean shaped. Pretty impressive for 140" focal length, unguided! The noise is well controlled without making the sky artificially black. Not sure about focus but a big SCT isn't the sharpest knife in the drawer when it comes to image quality. How did you focus?

Steve, part 2: A fun way to play with blue and yellow saturation is to convert your image to Lab colour. (With some steps noted.)

Dietmar: A good start. The colours are clearly visible. If you are going to do double stars and colour you may want to reduce the exposure time depending on the magnitude of the stars, that would solve the excessive flair and halos and get you rounder stars because the integration time is less. Never the less your experiment was successful.

Dietmar then analysed the image with his CCD Inspector software. It answered my question, wherein I noted the stars at the bottom-left of the field looked poor, deformed, while the top-left of the image was OK.

Diemtar: This could be due to a number of items, [such as] your camera sagging in the focuser or less than perfect alignment of the optics.

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