What causes redness in parts of an image

Gem (Grant) · #1 26-07-2013, 11:13 PM

Hi all,

I have had a few images lately with red to the side of the images. Always the same side. Seems to get worse as the night goes on (I think). What causes this? Is it that my darks are not taken at the same temperature as the image? My camera is an ATIK 320E. I used a stack of images plus darks and bias frames...

(Yes - there is a dust bunny there too)...

Please shed some light on this for me...

Octane (Humayun) · #2 27-07-2013, 12:28 AM

Has it been calibrated by flats?

I imagine it's light leakage.

H

Gem (Grant) · #3 27-07-2013, 07:40 AM

What do you mean by 'light leakage'? This image was stacked with dark and bias frames, however if I stacked without them the image was the same.

So do you think some flats would solve this problem?

Shiraz (Ray) · #4 27-07-2013, 08:34 AM

Quote:

Originally Posted by Octane

Has it been calibrated by flats?

I imagine it's light leakage.

H

agree with Humayun - looks like stray light. a green-to-red gradient like that might just be additional skyglow or even direct light from a streetlight or something hitting the front of the scope. That would be consistent with it changing through the night. was there anything different in the imaging environment when it appeared? If stray light/pollution, flats will not help

might be able to rule out any probs with the camera cooling - maybe stretch one of the darks and see if there are any odd gradients there.

Gem (Grant) · #5 27-07-2013, 09:37 PM

Thanks - I will give that a go. New scope location and I was imaging not too far above the roof, so that might be a factor.

Much appreciated.

tlgerdes (Trevor) · #6 28-07-2013, 07:14 AM

I had similar issues at times with my 8" newt with light leakage through/around the mirror, when the mirror was pointed towards the glow of my PC. Solved it by putting a couple of opaque shower caps over the mirror opening.

Gem (Grant) · #7 29-07-2013, 05:51 AM

These images were taken with an 80mm refractor... if I cover the end with the camera I am covering the fan of the CCD camera... I will have to take another look next weekend, weather permitting.

tlgerdes (Trevor) · #8 29-07-2013, 02:29 PM

Hi Grant,

It still could be stray light, ie your PC, that is being captured by your refractor. It could be gaps around you focuser that are letting in light, it could be being reflected off your dew shield.

Take note of direction of image in regard to ANY light source, you could find that the gradient you see is only in one direction from where you are imaging, or a certain orientation to where you setup your PC. This may help pinpoint the source of the problem.

Gem (Grant) · #9 13-08-2013, 06:54 AM

Thanks. Imaging in the suburbs means stray light is common. I will try to take more careful note of light sources.