Artifact problem

[andyo]

Hi

Got a chance to try out my new Atik 460Ex this weekend and new narrowband filters(except for the Ha), Things were looking good until I examined the subs and found an artifact that appeared on the O111 and S11 subs near the centre above the star cygni 52. It does not show on any of the Ha subs but first appears on the first O111 taken straight after the last Ha sub. I have taken darks and flats since and can see nothing showing on them.Last night I slewed to Vega and took some 5 sec exposures through each of the narrowband filters and the artefact showed on all three of them.I rotated the camera and the artefact also rotated suggesting its not a camera problem.It cant be the filters as its showing on all three of them so I checked the focal reducer which looks fine and I also checked the primary which also looks fine,I even loosened the primary and rotated that quarter of a turn but the artefact didn't move.I have checked the optical train for any light leakage and all seems ok. I am at an absolute loss as to what this is and how to solve it any help would be very much appreciated I have attached jpegs of each of the filters plus a dark and flat

Ha imageO111 imageS11 imageFlatDark

[D4N]

It looks like an internal reflection from 52 Cygni, what filters are you using?

[andyo]

Hi 

I am using these filters

https://www.firstlightoptics.com/narrowband/baader-narrowband-ccd-emission-line-h-alpha-filters-125.html

[Thalestris24]

Hi

Which way round do you have your filters? Try reversing them i.e. change to shiny side facing camera if currently facing the other way.

Louise

[andyo]

Just now, Thalestris24 said:

Hi

Which way round do you have your filters? Try reversing them i.e. change to shiny side facing camera if currently facing the other way.

Louise

Thanks Louise will have a look at that now,I didn't realise that made a difference

[D4N]

Interesting, those are the exact same filters that I use, the camera is nearly the same too, I have the version with the internal filter wheel.

I use the filters with the male thread towards the camera, it wouldn't be possible to mount them any other way with my setup although I guess it is possible to unmount the filter then re-mount it backwards.

[andyo]

4 minutes ago, D4N said:

Interesting, those are the exact same filters that I use, the camera is nearly the same too, I have the version with the internal filter wheel.

I use the filters with the male thread towards the camera, it wouldn't be possible to mount them any other way with my setup although I guess it is possible to unmount the filter then re-mount it backwards.

yes I have just looked and mine are mounted the same as yours male thread towards the camera would be hard to mount them any other way

[Thalestris24]

52 minutes ago, andyo said:

Thanks Louise will have a look at that now,I didn't realise that made a difference

It was just a suggestion/idea based on some other people's experiences... e.g. https://pixinsight.com/forum/index.php?topic=4776.0

I have filter drawers on some scopes and these allow easy reversal of filter orientation but obviously not so simple with filter wheels. 

Louise

[andyo]

2 minutes ago, Thalestris24 said:

It was just a suggestion/idea based on some other people's experiences... e.g. https://pixinsight.com/forum/index.php?topic=4776.0

I have filter drawers on some scopes and these allow easy reversal of filter orientation but obviously not so simple with filter wheels. 

Louise

thanks for the suggestion was worth a try but I think they had unmounted filters and I have mounted ones

[D4N]

Well it is possible to unscrew the locking ring on the filter mount and flip the filter over.

[andyo]

4 minutes ago, D4N said:

Well it is possible to unscrew the locking ring on the filter mount and flip the filter over.

Maybe but I don't think that would help in my situation

[D4N]

I would be tempted to do it with one of the filters just to eliminate it.  It seems up unlikely that they would have been put in backwards during manufacture but you never know.

[ollypenrice]

My guess would be stellar internal reflection as well. These are very rig-specific, I think, but the suggestons above are worth a go. And if they don't work you can fix it with a thoroughly scandalous and immoral dose of Photoshop thuggery...

Olly

[andyo]

53 minutes ago, ollypenrice said:

My guess would be stellar internal reflection as well. These are very rig-specific, I think, but the suggestons above are worth a go. And if they don't work you can fix it with a thoroughly scandalous and immoral dose of Photoshop thuggery...

Olly

Hi Olly, What causes these internal reflections and can anything be done about them.I have processed the image and did use the clone tool to remove it and it worked well but will I have to do this on all my images from now on.

Another question is why didn't I get these reflections with the 314L+ could that be due to the different sensor size 

[ollypenrice]

I've no idea why they are so variable, but all sorts of things could be at play. The distance between the glass surfaces, the effects of different chip micro lenses and so on.

I tend to attack these artefacts in Curves. Make a copy layer, work on the bottom, pin the background sky next to the artefact and pull down the curve above the pin. Then make the top active and erase just the bit with the artefact.

Olly

[andyo]

3 minutes ago, ollypenrice said:

I've no idea why they are so variable, but all sorts of things could be at play. The distance between the glass surfaces, the effects of different chip micro lenses and so on.

I tend to attack these artefacts in Curves. Make a copy layer, work on the bottom, pin the background sky next to the artefact and pull down the curve above the pin. Then make the top active and erase just the bit with the artefact.

Olly

Thanks for that olly

[andyo]

thanks everyone for the replies.after a few tests this evening I can confirm that it is a reflection artefact and it is showing in all filters L R G B Ha O111 S11. When I moved the mount it mirrored the movement and I was actually able to focus the artefact.

[andyo]

OK it looks like I have got to the bottom of this problem.When I had the Atik 314L+ I needed to get some adaptors and extensions to get the required 55mm distance to the focal reducer. This meant that I could not use the adaptor supplied with the filter wheel as the nose piece was to long. After looking into the filter wheel I noticed the originally supplied adaptor has a type of baffle at the back of it to block stray light. Using the new extensions I had pieced together this was not a problem with the smaller chip of the Atik 314 however with the bigger 460 chip I believe it is responsible for this artefact. I tested this out tonight by slewing to Vega and taking some short exposures sure enough the artefact was clearly visible so I then changed the extension to the supplied one,admittedly the spacing will not be correct but for this purpose I would not think that would matter. When I took some more exposures after focusing the artefact was no longer there.

I have now emailed FLO regarding getting a custom adaptor made,I have attached some images to show the difference between the adaptors.

Andy

[ollypenrice]

That is very good information on a common problem. Sticky?

Olly