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M45 - unusual glow in images and unsure why


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hey guys

Below I enclose an image of M45 I took last night. It consists of 19 x 5 min lights. 36 x 5 mins darks I took in the fridge at roughly the same temperature, 30 x flat fields taken with a new light box I built and 143 bias frames.

Now the flats seem to be working great for the vignetting across the picture except for a strong light gradient that spreads from the left of the image.

My question is this: is this glow a problem with the flats (which when I stretch the master flat does not have this strange glow) or could it be something else? maybe amp glow? what do you guys think?

I know the neighbours switched on their lights a fair few times last night could this be an issue?

here is the image:

m45withgradient.jpg

and for the record here is a copy of the flat:

masterflatiso400.jpg

any advice would be appreciated thanks

Mark

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With a DSLR? Did you cap the viewfinder eyepiece? Light can leak in through the eyepiece if you leave it uncapped, this may be an issue in long exposures if there is significant stray light at your location.

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brianb - hmmm thats a good point I never capped the view finder it could be an issue I will look into it :)

jgs001 - ha the diffraction spike I have had before, its due to when I collimate my scope and I accidentally tilt one set of support struts for the secondary mirror then it adds an extra set of diffraction spikes. I just never noticed it at first so when I set my camera taking photos I went inside and it wasnt until I processed them did I spot it.

I noticed the odd reflections to, I do wonder why that is, maybe water or ice formations on the mirror?

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I think I figured out what caused the glow. I never realised that my skywatcher 200p lets light in from behind the primary mirror. That combined with the fact that a bright street light shines over some of my garden and that the back of my telescope was partially in the light has let the street lamp light leak into the back of my scope hence the glow from only one side.

Mystery solved... just means I have to take yet another picture of M45 minus light from the street lamp gutted :)

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Glad you figured it out. Easy to deal with too. As for the viewfinder, I've done some experiments and leaving the viewfinder uncovered can have an effect, but I found it was only with directly incident light on the viewfinder. I do use the viewfinder cap if I'm shooting darks in the garage though as I have to turn the light on to see what i'm doing.

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