Does Atik EFW2 work with Atik 383L?

[gnomus]

I have an Atik 383L and an Atik EFW2.  I use the 7 position carousel which takes 36mm unmounted filters.  I use Baader filters - LRGB and the NB set.

Back in January 2016, I posted about an issue I had with horizontal lines in my flats.  These were producing artefacts in my final images.  Here is one of the Ha flats that caused concern:

The chap from Baader filters suggested a couple of things.  One of these was to reverse the orientation of the filters in the filter wheel.  This made no difference.  The second thing he suggested was to put some spacing between the wheel and the camera.  This did actually work.  Indeed, as I increased the spacing, I could see these lines move closer to the edge of the frame.  When I got to 5mm of spacing, the lines disappeared.

It seemed odd to me that Atik would produce a filter wheel and camera combination that required a spacer between camera and wheel.  I assumed that this was just a one-off thing.  I hadn't heard of anyone else having these issues and perhaps there was 'just something' about the particular wheel or camera combo I had that was giving me these issues.   

I am now in the process of putting together a dual rig.   As part of this, I got hold of a second Atik 383L (used).  I thought I would try this with my EFW2.  I took the spacer out and, lo and behold, the horizontal lines came back.  This time I could only see the line at the bottom of the frame.  Once again, as I increased the spacing between wheel and camera the line moved to the edge of frame.  This time I had to use the 5mm ring and a couple of thick Delrin spacers to eliminate it.  (I still have a very slight line at the very bottom of my SII flats with the second camera).  

The lines are seen in flats taken through all of the NB filters and they appear also in the Blue flats.  They produce visible effects in the calibrated images.  My exposure length varies depending on which filter I am using but the Blues get shot at around 8 seconds and the NBs take between 12 and 15 seconds.

I need to get a second filter wheel and filters to go with my new (used) camera.  I don't now know if I should get a second EFW2 - It is getting a bit tedious having to do battle with these issues and I wonder if I might get a better result with the SX USB filter wheel.  

Does anyone have any idea what might be causing these, and what could be done to eliminate them?

And then there is this.....  I have noticed that in my original Atik 383L there is a second artefact.  Another image should show it clearly - this is a blue flat - the spacer is in place so there is no line, but look at the lower right corner:

I've exaggerated the processing to show the effect.  Once again this 'shadow', has an effect on the calibrated images producing an 'overcorrection' in the lower right of the frame - the sky in this part of the processed image becomes much lighter and I need to resort to considerable Photoshop jiggery-pokery to sort it out.  This is something that I would rather not have to do. 

Interestingly the 'new' (used) Atik that I purchased does not show this effect.

I don't really know why I am getting horizontal lines in my flats, but it seems to me that it must be the edge of the sensor window reflecting back off the filter.  

I have absolutely no idea what I should do as regards a second filter wheel and filters. 

I did e-mail the supplier of camera and wheel a week ago, but so far have not had a response.

 

             

[ollypenrice]

My guess is that the cause will be internal reflection, light shunting between the chip window and the reflective side of the filter. That would explain why varying the wheel spacing would have an effect. I doubt it's the wheel itself, which simply holds the filters in place. Guesswork, of course.

Olly

[gnomus]

I'm sure you're right, Olly.  What I don't know is if the spacing in the SX wheel would be such that I would get more or less of a problem.  I also don't know if it would be better with bigger (or smaller) filters.  (I suspect I'd get it no matter the size of the filters.)  Or would it be less of a problem with Astronomik (or **gulp** Astrodon) filters instead of Baader.  

But the overall thing that still puzzles me is, why am I getting it but no-one else seems to be.  I would have thought 383L + EFW2 would be a common combination, and the 36mm filters seem an obvious choice for that pairing. 

I should point out that I get the same issue irrespective of scope (I've tried 4 scopes now from F/L 350mm to 2030).

[geordie85]

I use an atik 383l with the SX 7 position filter wheel and 36mm unmounted Baader filters and have never noticed anything like this on my images.

Although I'm still new to ccd imaging and have yet to take any decent flats as I'm still trying to work out the best way to take flats that I am able to do (my laptop screen doesn't cover my 8 inch tube fully)

[Davey-T]

6 minutes ago, geordie85 said:

Although I'm still new to ccd imaging and have yet to take any decent flats as I'm still trying to work out the best way to take flats that I am able to do (my laptop screen doesn't cover my 8 inch tube fully)

I made a light box for my 10", just a box with a hole covered in white opaque plastic that fits over the end of the scope and has four halogen bulbs in the box and a dimmer to alter the brightness.

Or you could try sky flats

Dave

 

[gnomus]

 

21 minutes ago, Davey-T said:

I made a light box for my 10", just a box with a hole covered in white opaque plastic that fits over the end of the scope and has four halogen bulbs in the box and a dimmer to alter the brightness.

Or you could try sky flats

Dave

 

I have one of those Gerd Neumann panels.  It produces the same result.  It ain't the source of light that's causing this. 

[geordie85]

1 hour ago, Davey-T said:

I made a light box for my 10", just a box with a hole covered in white opaque plastic that fits over the end of the scope and has four halogen bulbs in the box and a dimmer to alter the brightness.

Or you could try sky flats

Dave

 

I've tried sky flats and they were washed out even after 1 second. 

Maybe I just need to go buy more white t-shirts :-P 

 

Can you post a pic of your light box so I can possibly try to create one of my own 

[Davey-T]

10 hours ago, gnomus said:

 

I have one of those Gerd Neumann panels.  It produces the same result.  It ain't the source of light that's causing this. 

Wasn't suggesting it was Steve, I just found it easier to use a dedicated light box for bigger scopes, I use a light panel for refractor flats.

Don't know what to suggest for your problem, sell it all and buy  QSIs ? 

Dave

[gnomus]

FLO have kindly sent me a new set of LRGB filters to try.  I agree with Olly that this must be a reflection, most probably off of the filter. However, is it possible that the reflection is coming off something else?  The filter wheel carousel is black but it is that slightly shiny black, just as almost every other surface is in there.  I wonder if covering everything in a matt black paint would help.  If it is a filter issue, and the replacements don't help, what about a different brand?  Has anyone tried these Astronomik 'Deep Sky' filters?

[ollypenrice]

It could be the glass of the chip window reflecting light back towards the filter. I have never had any issues with Baader filters other than the indifferent performance of the OIII, with its tendency to throw up star haloes. I've used the 1.25 and 2 inch filters (two sets of the latter) in at least half a dozen scopes and with three makes of filter wheel - Scope Technix manual, 2x EFW2 and SX. I think this is likely to be a rogue specific to one component.

Regarding QSI, one of my friends is delighted by a recent firmware upgrade which, he says, has allowed calibration to work properly for the first time.

In a nutshell this game is full of inventive and flexibly-minded gremlins who love to come from unexpected directions at the first sign of a clear night.

Careful with matt black paint. Those which are dye based tend to be reflective in IR. You need a pigment based black paint such as those intended for stoves and barbecues. For a lengthy and learned discourse on this matter here's the source: https://www.sbig.com/about-us/blog/flat-fields-the-ugly-truth/

Olly

[gnomus]

Thanks Olly.