RickS recently posted the following in a thread in the Deep Space imaging forum:
Quote:
I haven't run into those weird reflections with my ASI1600 yet but it's probably just a matter of time. I have a few thoughts about how you could reduce the effect in processing...
Cheers,
Rick.
Rather than hijack that thread I thought I'd start a new one here (hopefully Rick will wander past and comment). I found the following tutorial (http://trappedphotons.com/blog/?p=616) which seems to be a good method but when the reflections are as bad as the ones I have in the attached image, it becomes too difficult. I'd be keen to hear anyone's ideas about a good solution (other than buying Astrodon narrow band filters ).
That is pretty useful especially for filter reflections caused by non AR issues. Sadly the diffraction pattern from the ASI1600 is different but the technique would work well for some of the cheaper filters.
So is this problem specific to the ZWO camera and not the QHY163 which has AR coating? Just wondering as I'm thinking about a mono cam. Sorry to hijack Kevn.
I believe I have a fair number of sub examples in my library but I will need to track them down. Once I discovered the problem I resorted to framing Alnitak out to avoid it. I use Baader narrowband filters, but I believe it also happens with Astrodons.
So is this problem specific to the ZWO camera and not the QHY163 which has AR coating? Just wondering as I'm thinking about a mono cam. Sorry to hijack Kevn.
The reflections are off the sensor cover slip, not the camera window so the QHY version shows the same effect... or so I have read on CN.
Quote:
Originally Posted by glend
I believe I have a fair number of sub examples in my library but I will need to track them down. Once I discovered the problem I resorted to framing Alnitak out to avoid it. I use Baader narrowband filters, but I believe it also happens with Astrodons.
Ben said he would get me a copy of his Oiii master which is a textbook example of the artefact, so no problem if you can't find then Glen.
Rick I will upload a recent stack with terrible halos.
Btw, are the halos from zwo filters or the camera itself?
Bear with the noise, it's WIP :p
Thanks, Logan. The halos are mostly due to the sensor (microlenses and reflections from the sensor cover glass) but I wouldn't rule out filters having some effect as well.
Both are shot using both the ASI1600MM and an Astrodon OIII 3nm filter. My image is more stretched I think. An Astrodon filter (sadly) seems not to be a solution.
In processing, once a liner fit was applied to the O3, using Ha as a reference, some of the issue was quietened down somewhat.
Thanks, Logan. The halos are mostly due to the sensor (microlenses and reflections from the sensor cover glass) but I wouldn't rule out filters having some effect as well.
Interesting. I have ZWO filters but the narrowband ones give really bad reflections where the LRGB ones don't.
Thanks, Logan. The halos are mostly due to the sensor (microlenses and reflections from the sensor cover glass) but I wouldn't rule out filters having some effect as well.
That’s pretty much it. The reflections are caused by the interaction between the microlens’ and the cover glass which isn’t AR.
This means that filters without good AR coatings are likely to be more affected (thinking ZWO narrowband) so you may get worse reflections on an ASI1600 than ASI183 on the filters themselves and not just the microlens diffraction.
So, Kevin and Logan have "bullseye" halos which look to me like multiple reflections from a filter external to the camera. What filters are you guys using?
Ben has a strong case of the more complex reflected microlens diffraction pattern. I had a quick play and managed to ameliorate this to a reasonable extent but not enough that I was happy.
I probably won't get a chance to do much more until the weekend and will report back on any successes... or failures
So, Kevin and Logan have "bullseye" halos which look to me like multiple reflections from a filter external to the camera. What filters are you guys using?
I have a full set of ZWO filters. This particular image was the ZWO 7nm Ha filter.
Sorry to jump the gun but was having too much fun trying things! As a first step I followed Ricks advice and created a range mask, isolating the reflections and leaving the star, and then replaced the reflections with an estimate of the background (MMT). I had to soften the mask a little and still ended up with some residual halos. I did this on the three Ha, S2 and O3 tone maps and also on the Luminance (which in this version is just Ha). A start perhaps? Before and after pics below.
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