CCD camera smudge

[sshenke]

Hello all, I would appreciate your help on this problem please. I have been having a huge problem with capturing dso images since October last year, having previously managed to obtain good images of a few galaxies and nebulae ( I started doing this in July last year). For the last few months though I haven't captured even a single decent image and have been blaming the dew, refractor, filter etc. But finally I seem to have got to the bottom of it or so I think. As you can see in the attached images, there is a crescentic area of artefact near the centre of the image. Initially I thought it was the filter, but when I imaged without the filter, it is still there. I cannot see any obvious problem in the optical window of the CCD sensor, but still cleaned it properly with isopropyl alcohol and went onto test it last night and noticed this weird thing. I took 2 round of  1 frame each of lrgb images of m31. I didn't touch the scope or the capture software until the 2 rounds were completed and what I notice is that the smudge was there in round 1 images ( postfixed 1..red1, green etc), but not in round 2 images. I am not sure if it is due to drop in visibility as there was some cloud cover during round 2. Also I cannot see this artefact on images taken during daytime, such as of the sun. It moves independently of the image with the movement of the telescope, which is why I think it is on the CCD camera. This is ruining the images significantly and the unpredictability of it occurring is another frustrating thing. Would appreciate the help of the experienced and the wise please. The image with the title of andromeda 1 was taken about 2 months ago. I have also previously cleaned the primary and secondary mirrors thinking that that's where the problem was. 

Scope: sky watcher 130 pds

Zwo asi 1600mm camera

Thanks

[carastro]

Is this the only target you have tried this with?  Just wondering whether is is some sort of reflection. 

Carole 

[sshenke]

8 minutes ago, carastro said:

Is this the only target you have tried this with?  Just wondering whether is is some sort of reflection. 

Carole 

Thanks Carole, yes this is what I have been targeting primarily, as it was an easy target to acquire, given the problems I have been facing. But I did try a few other things like veil nebula, but have not been able to do any substantial imaging with these targets because of the cloud cover. I am going to try again tonight with a differ ent target

[souls33k3r]

Could it possibly be dew forming on the camera optical window?

[carastro]

It would be useful to point your camera in a different direction and see if you get the same thing.  If it doesn't happen elsewhere then we can exclude lots of things, as I am suspicious that it is a reflection of something, maybe a light that somehow gets into your optics only in a particular position. .  The guys are more technical than me with with this sort of thing, so lets hope some-one dives in soon to help you out.  

Carole 

[sshenke]

1 hour ago, souls33k3r said:

Could it possibly be dew forming on the camera optical window?

I am not sure if thats the case, because of 1. why would the dew always form on the same place- the optical window of the ccd camera looks clean to me 2. If it is because of dew, I would expect the images on the second round to be worse because of dew getting worse the longer the scope is outside. This is what I think, may be I am wrong, but thanks for looking into this issue. Really appreciate it

 

[MartinB]

The arc artefact is adjacent to a darked part of the image.  I wonder if your filter  wheel isn't rotating properly.  This could cause the small arc as a result of reflection and the dark edge.  If you can it is worth having a look at how accurately the wheel is placing the filters.  

[sshenke]

2 hours ago, MartinB said:

The arc artefact is adjacent to a darked part of the image.  I wonder if your filter  wheel isn't rotating properly.  This could cause the small arc as a result of reflection and the dark edge.  If you can it is worth having a look at how accurately the wheel is placing the filters.  

Thanks, I will look at the rotation of the fw.

Had very clear skies last night, but did not get any proper images at all. I can see the arc more clearly in the pictures of the pleiades and I can see the same sort of smudge in the picture of M33 ( that picture is a 120 sec exposure of M33!!!!).  Looking through the objective port of the scope, I noticed that the secondary mirror is off centre, so I think collimation is definitely a problem. I can also see the bevelled edge of the secondary mirror being prominent and I wonder if there is light coming from the primary mirror that is being reflected off this bevelled edge on to the camera causing the arc. 

[glowingturnip]

think you need to get yourself a cheshire eyepiece and sort that mirror out