HELP! Why do i have a light patch in the middle of all my photos!

[Glambert]

Hi all you will see on my images below, particularly in the picture of m81...i appear to have a glow that is the same as the ligh captured in the galaxies. As a result when i am editing on photoshop the more i bring out the galaxies the more i bring out this central glow! I am imgaing with a light pollution filter with a zenithstar 61 and a canon dslr. I have imaged on nights when the moon is out but can anyone help me here? How do i avoid this in the future either via my setup or my processing?  This is ruining my photos and my drive for me to take anymore as when i try and bring out detail the whole central part blows out as well!

Edited January 28, 2021 by Glambert
Spelling error

[wxsatuser]

Are you using flats?

 

[Glambert]

Hi, yes i am using flats and darks. 

[wxsatuser]

Try without flats and see if it's still there.

[Glambert]

3 minutes ago, wxsatuser said:

Try without flats and see if it's still there.

The bottom image was taken without flats. It is less prominent but is still there. 

[wxsatuser]

May be the Moon causing it, would expect gradients but this looks more like vignetting.

May be someone with a similar set up can give some idea.

[Glambert]

14 minutes ago, wxsatuser said:

May be the Moon causing it, would expect gradients but this looks more like vignetting.

May be someone with a similar set up can give some idea.

Thanks will see if anyone else suggests anything. I'm worried it is a problem with the scope or if it is just a problem with the camera sensor. Would adjusting my adjustable field flattener help do you think?

[wxsatuser]

What flattener is that, does it suit your scope?

[Glambert]

2 minutes ago, wxsatuser said:

What flattener is that, does it suit your scope?

Yes it is the dedicated field flattener for the z61 but it is adjustable. 

[wxsatuser]

May be that is the problem.

Make sure it is adjusted correctly for a dslr and it's t-ring
Canon and t-ring should be about 55mm+/- back focus, cannot help with adjust as not seen or used one before.

[Jamgood]

Are you using a dew shield? Using one can help with stray lights from houses, surrounding spaces, etc. Can easily make one out of cardboard.

Was there any build up of dew on the glass? Are you using dew heaters?

How long was your gear outside before you started imaging? Maybe need a little longer to cool down in these temperatures or as above, been out a while and the weather is affecting things.

These things are sent to try us, don't give up the battle. It's half of the fun.

[Glambert]

18 hours ago, Jamgood said:

Are you using a dew shield? Using one can help with stray lights from houses, surrounding spaces, etc. Can easily make one out of cardboard.

Was there any build up of dew on the glass? Are you using dew heaters?

How long was your gear outside before you started imaging? Maybe need a little longer to cool down in these temperatures or as above, been out a while and the weather is affecting things.

These things are sent to try us, don't give up the battle. It's half of the fun.

Hi thanks for the reply yes it has a dew shield built in and i am using a dew heater around it. As the dew shield was extended i couldn't really see any dew on the glass i was outside some time and it was very cold. I have not been able to take a single set of frames yet that once stacked don't have a central glow meaning i soon as i bring out details in the galaxy my image is ruined as it comes out in the centre. I might play around with the field flattenner the problem is on a single shot it doesnt show so i only know once they are stacked and i start to process the image!

[BCN_Sean]

May seem like a slightly odd and simple question, but did you cover the viewfinder of the camera when you were shooting these?  Light coming in through the back of the camera can create bright spots on an image which do look like a form of vignetting which is more noticeable the longer the exposure time.  Most SLR are supplied with a little plastic clip and that replaces the eyepiece around the viewfinder to cover it; but if not a bit of electricians tape does the same thing.

It's an often overlooked thing, but it is one of the simplest to check that doesn't require extensive work to the setup to diagnose or rule out.

[Jannis]

It looks like a flat frame issue to me.

How do you take your flat frames? I've had issues trying to take flats in daylight before due to light leaks in the telescope/focuser, as well as trough the viewfinder (before i knew i had to block that off). These days i simply take flat frames pointing up in the sky a bit before the sun comes up, or after it goes down and it have worked so far.