Atik 383 Flats

[gnomus]

I've had continual problems with reflections in my flats.  I have an Atik 383L, an Atik EFW2, and I use 36mm unmounted Baader filters.  It seems that when using the camera and wheel 'as intended' I get reflections.  I see these especially in my flats, but I think they are there in the images too.  They do not calibrate out - I am left with lines in my images and I either have to crop them heavily or use blunderbuss processing techniques, which inevitably leads to some degradation in image quality (and my images are already quite degraded enough).

I have posted about this problem before: https://stargazerslounge.com/topic/260450-horizontal-lines-in-flats/ and https://stargazerslounge.com/topic/269119-does-atik-efw2-work-with-atik-383l/

There is a solution, but it is not ideal.  I thought that I would provide an update as to my progress and post my solution.  If anyone has any other ideas I would consider trying them out.  I am struggling to believe that I am the only person having this problem.

First off, here is the issue - it appears to me to be a reflection of either the optical window edges or the sensor itself (I've pushed the contrast a bit to make the issue obvious in a reduced size JPEG):

The issue is most obvious in the NB filters, but it is there in the RGB too - perhaps worse in the blue filter.

• I have tried the set up on 4 separate scopes - 3 x refractors and 1 x SCT - there is no difference
• I have tried two different 383L cameras - they both cause this problem
• I have tried 2 different sets of Baader LRGB filters (thanks to FLO for supplying the second set) and a set of Baader NBs - no difference
• I have tried reversing the orientation of the filters in the carousel (suggested by the chap from Baader) - no difference
• I have tried a different filter - a Chroma Green kindly supplied by Bern at Modern Astronomy - no difference (indeed maybe the reflections were a little more obvious - I've posted the Chroma version)
• I have tried 3 different methods of taking flats: an LED panel; a Gerd Neumann EL panel; and sky flats with a pillowcase
• I had one camera back to Atik who tried blackening the optical window edges.

  The chap from Baader also suggested putting a spacer between the camera and the wheel.  This started to work.  As I added spacers, the lines moved to the outside of the frame.  Eventually they went away altogether.  I was able to lose the lines at 7mm of spacing on one 383L.  I needed 7.5mm of spacing with the other.

The spacing does not seem to make the vignetting any significantly worse, so this is a 'fix'.  On the other hand if you are considering using an OAG, then being forced to add that 7.5mm could be significant.

 Am I really the only one having this problem?

[Davey-T]

I'm curious why it occurs on the long edge of the sensor ?

I use Atik EFW2 and Atik OAG with 1.25 Baader filters but with Atik314L with no problems.

Have you tried a 1.25" filter just for the hell of it ? may get no lines but worse vignetting but at least that can be processed out.

Dave

[gnomus]

Thanks Dave.  In fact you can see a full rectangle in the flat - the bottom is very obvious but you can see the sides and top too.  It has to be something to do with the sensor window.  I thought I was being 'reet smart' getting the 7 x 36mm carousel, now I wonder if I might not have been better off with a 1.25" set up (those filters are cheaper too).

It would mean getting a different carousel - £59 and filters (???? price).

I'm about to embark on a large-ish (20+ hour) project and I have things working at present.  I may look at the 1.25" option once that is done.   

[Davey-T]

The size difference between 36mm unmounted and 1.25 pretty minimal.

Pity you're not a bit closer or you could borrow mine to try now I've finished imaging incy wincy galaxies for this year.

Picked up 10Micron mount this morning so that will be occupying all my time getting it set up and working for the autumn.

Dave

[gnomus]

Congrats on the mount - hope you enjoy it.  

[sloz1664]

Hi Gomus,

I have a SX 5 position electronic filter wheel loaded with 1.25" HaLRGB Baader filters you can try, if you like.

Steve

[gnomus]

That's very decent of you Steve.  I may take you up on your offer.  Barry Wilson has suggested to me that it could be a light leak issue with my filter wheel.  I will explore that option first.  Nottingham-wise are you N, S, E or W?

Steve

[Singlin]

I had a light leak between my flanges on my Moonlight focuser.

I used electrical tape to eliminate the problem.

Also the led lights from my Sitech II controller,Focuser hub etc were causing stray light.I placed some tape on those too.

[Physopto]

If you can get hold of a camera black bag it may be helpful to find out about light leakage. I used one years ago to change out partially used film, without rewinding it into the cassette. It consists of a light tight bag with a zippered bottom end and two arm holes . You can un zipper it and place it over the camera and filter housing, then gather the open end tight around the scope. Cannot do it for too long as the camera will overheat. http://www.ebay.co.uk/itm/Good-Film-Changing-DarkRoom-Bag-Dark-Room-Load-Photography-Zipper-Camera-Bag/201587336535?_trksid=p2141725.c100338.m3726&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20150313114020%26meid%3Da14b892760724a89ab3c7b643fcb1ff5%26pid%3D100338%26rk%3D1%26rkt%3D8%26sd%3D161432578673

 

[gnomus]

2 minutes ago, Physopto said:

If you can get hold of a camera black bag it may be helpful to find out about light leakage. I used one years ago to change out partially used film, without rewinding it into the cassette. It consists of a light tight bag with a zippered bottom end and two arm holes . You can un zipper it and place it over the camera and filter housing, then gather the open end tight around the scope. Cannot do it for too long as the camera will overheat. http://www.ebay.co.uk/itm/Good-Film-Changing-DarkRoom-Bag-Dark-Room-Load-Photography-Zipper-Camera-Bag/201587336535?_trksid=p2141725.c100338.m3726&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20150313114020%26meid%3Da14b892760724a89ab3c7b643fcb1ff5%26pid%3D100338%26rk%3D1%26rkt%3D8%26sd%3D161432578673

 

Thats a good idea Physopto.  I'd already decided to do something like that.  I have sheets of neoprene kicking around the house.  I'll cobble something together.

[Davey-T]

I get light leaking in somewhere on flats taken with the Atik314, Atik OAG, EFW2 combo so I only take them in the obs'y in the dark otherwise I have to cover the camera.

Doesn't look like yours though more of a horizontal light streak about a third of the way down.

Dave

[Physopto]

25 minutes ago, gnomus said:

Thats a good idea Physopto.  I'd already decided to do something like that.  I have sheets of neoprene kicking around the house.  I'll cobble something together.

The only other thing I can think of is the CCD flush between images causing a problem. You could try setting  a delay after the flush to allow extra electron charge to clear! Bit dubious about that though!

[gnomus]

15 minutes ago, Physopto said:

The only other thing I can think of is the CCD flush between images causing a problem. You could try setting  a delay after the flush to allow extra electron charge to clear! Bit dubious about that though!

Thanks again, but this is not an electrical issue.  When I introduce a spacer between the wheel and camera the lines move towards the edge of frame.  When I introduce enough space (7.5mm) they disappear altogether.  This is reproducible regardless of the state of the camera.  And it is consistent from first frame to last.

[nucdoc]

I have followed this with interest as I have the same camera, but Astronomik filters, 2 inch in a Starlight express USB wheel.  I can see no such line on either raw flats, or masters  of LRGB or Ha.  

One thing I did not see in your attempts to resolve this is a flat image with no filter, If possible can you shoot one without the filter wheel, and then with the filter wheel but no filter in the wheel, I assume if it is related to the camera window you should see it even with no filter in the wheel.

 

Good luck 

 

Mark

[gnomus]

I've tried no filter.  I didn't see anything, but the line is much fainter in my Lums too.  

The other day I wrapped all of the camera and wheel in opaque material.  I was pretty sure I had averything covered.  At the very least I will have significantly cut down the amount of light getting to wheel and camera.  Anyway, it made no difference to the lines.  So I think I can rule out light leakage.

I believe the lines are the edges of the sensor window reflecting off the filter.  If it was just an internal camera issue, I would not be able to 'solve' it by increasing the space between filterwheel and camera.  I do wonder if less distance between filter and sensor would also elminate the issue. - that may be why you don't get it with the SX wheel.  That is probably why cameras with built in wheels seem unaffected.  Of course I cannot shorten the distance.

[nucdoc]

I had a look at the drawing of both wheels, it looks like I got lucky.  My filter wheel is 7mm wider than yours, that may well be the difference.

SX filter wheel

 

 

Atik EFW2

[gnomus]

That is spooky.  I have had to put 7.5mm of spacing rings between wheel and camera to eliminate the lines.    

[Physopto]

May sound daft but you can shorten the distance. Temporarily fix the filter to the camera and hold it to the scope. Use your opaque material wrapped around the setup and take a flat. I.e. No filter wheel. See what happens. Just the focus to get the same before you can get the result. As long as no light leakage then it should prove the point.

Derek

 

[sloz1664]

On ‎03‎/‎06‎/‎2016 at 08:52, gnomus said:

That's very decent of you Steve.  I may take you up on your offer.  Barry Wilson has suggested to me that it could be a light leak issue with my filter wheel.  I will explore that option first.  Nottingham-wise are you N, S, E or W?

Steve

Sorry for not getting back sooner...manic weekend.

SW Notts. Long Eaton

 

steve