Misaligned Optical Path on my C11" EdgeHD?

I personally doubt that tilt would cause this effect.

First, tell me how well your images calibrate.

John

Ok Bruce.  Thanks for that.  I think that the first thing to figure out is why calibration isn't working.  When flats don't work there are two very common problems.

1) Stray light
2) Too much vignetting

From what I can see in the data you've supplied, stray light is my most immediate concern.  Remember that calibration only corrects multiplicative errors and since stray light is an additive error it won't calibrate out.  Stray light can come from:

1) Stray reflections from connector tubes or other structures within the light path,
2) Poor baffling in a two mirror system,
3) Excessive scatter from a corrector plate,
4) Light leaks in your imaging path or in your camera, or
5) Something else that I can't anticipate.

The concentric rings that you see in the flats and that appears in DBE corrected data is a dead giveaway that you have stray light reflecting from the inside of a round tube some where.  In this situation, I always recommend first pulling the camera, pointing the scope outside during the day at a bright scene, and looking backwards through the system.  Look for any small strays from shinny inner surfaces.  Those are what you have to fix.  Very flat black paint (like Mussu Black) or black flock paper will go a long way toward fixing this stuff.

I'm not completely sure why you are seeing such a big gradient but let's fix one thing at a time.  You have to be relentless to kill all the strays in you system first.  Then repeat the experiment to make sure that the bright rings are gone.  Then let's figure out what's causing that big gradient.

John

Bruce, is it only the L filter? before you disassemble your Edge, maybe make sure that note one of the filters is a lemon. I actually just had such a case (for my R band), which looked similar. More clearly visible, if you have a faster optics to your disposal. you could rotate the filter in the wheel a bit (easier with unthreaded filters) and see whether the direction of your asymmetry changes - that was the case for my bad R filter - it got exchanged and now all is bright eyes and bushy tail

Matthias

Thanks for everyone's input.  No luck so far.  Spent several hours looking into the OTA after removing the camera with a very flat panel light shining into the corrector plate and no reflections noticed.  I checked the camera, FW, and filters for anything loose and the filters do align in the FW.  I also checked for any other loose peripheral extension tubes but all seem ok.  I did a few frames last night but the result was the same with the broadband filters.  So, unless I take the scope down from up in the observatory, I'm not sure what is next to try.  Frankly, I am trying to talk myself into a 12.5" Planewave.  Very frustrating.

Problem resolved……………………..

After a second round of examining each component of the setup, I found the major culprit. One of the push screws on the camera tilt plate was screwed down further than the other two, creating a gap less than a 0.5mm.  It was just enough to let light in.  While the purpose of a tilt plate is to use it this way to adjust for tilt, I have read others having this issue as the gasket on the ASI6200 is not thick enough to fill in the space created by using the push/pull screw pairs.  In addition, I redid the velcro strap that holds the Optec FastFocus Secondary Mirror wiring system in place as a small shiny piece of metal was exposed near the corrector plate.  

I took a series of 2-minute LRGB exposures, new flats, and dark flats and the result was near perfect images.  The concentric rings and bad obstruction are now gone.  

Thanks to all for their valuable input.  Another learning, albeit frustrating, experience.  Just when I think I have leaned and solved everything in this hobby, something new or unexpected arises!

Good to hear you solved your issue. Anyway, I am puzzled: what has straylight to do with off-centric illumination? I have had the same issue in all my scope/camera combinations so far (which are quite a number, mono and OSC, reflectors and fracs). Never had a perfectly centered light cone for whatever reason.

I found the major culprit. One of the push screws on the camera tilt plate was screwed down further than the other two, creating a gap less than a 0.5mm.  It was just enough to let light in.

Hi Bruce, perhaps I missed it, but what did you do to solve the issue? Did you unscrew the push screw or did you somehow tape off the gap? 
Just wondering, as the first solution would have changed tilt and gap, while the second solution would only have changed gap.
I have seen the issue you demonstrate as well in my setup, but never bothered too much, thinking it would be a <100% aligned filter. Your post suggests it might be worthwhile looking a bit further though….