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Diffuse glow/halos on bright stars - causes and solution

Acquisition Deep Sky Artifacts Help Needed
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robonrome avatar
robonrome avatar
I seems to be struggling more than usual of late with diffuse halos or what I might call "glow" around stars (e.g. not "hard" halos) ... pretty much at a scale matching star brightness. Just a quick snip from a half processed image below to illustrate - this is at 300% hence rough quality.

Using an APM LZOS 130/780 (F6) refractor, ASI2600MM and Antlia SHO Pro 3nm filters. Typically doing 5min or 10min exps.

Started noticing this "glow" around stars in processing moreso in recent weeks and not sure if it's appearing more in reality or I'm just noticing more... I have been using a straight flatenner more lately and do feel my raw stars are a little less "sharp" when using a straight flatenner (Riccardi Flat 1) compared to when I use a 0.75x reducer (Riccardi m63), so not sure if that's a factor ... perhaps poorer seeing combined with longer (unreduced) focal length also playing  apart here but not sure if seeing is an worse etc.

Found this annoying enough to cut short imaging the Dolphin Head nebula linked dolphin head as i felt the star glow was getting distracting. Want to see if I can get it sorted before I invest 40-50hours on a target.

So what do we all think? - is this pretty normal and I just need deal with it in processing... is it time to upgrade to Chroma or AD filters...any other suggestions.

I find it curious I notice this more when using a high quality flatenner and not the reducer so much...does that make any sense?

thanks for your advice.


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Geoff avatar
Geoff avatar
It’s not normal. Could be dew on the optics or high thin cloud.
Dave Rust avatar
Dave Rust avatar
I get a similar effect with filters with a mirror-like diaelectric coating.  On my rig, it's essentially an infinity reflection between the filter and the glass IR plate in front of the sensor.  The result looks like a sphere.
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Dale Penkala avatar
Dale Penkala avatar
1st thing I go to when I see this is what @Geoff has already mentioned. Dew or a hazy high thin clouds causing issues.

But if you want to see if its your corrector I’d shoot an image with and without the flattener and compare to 2 images. That way your seeing the results of the change in a very short period of time to make a decision.
I also agree with you in the sense you want to get this figured out before investing the time in the image you want to go after!

Dale
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andrea tasselli avatar
andrea tasselli avatar
Normally I get this kind of glow around bright stars with thin clouds and/or hazy conditions, most likely when the object is low on the horizon. As I use heater bands all the time dew collection on the lens isn't an explanation. And I don't use filters either.
Dave Rust avatar
Dave Rust avatar
https://imagimedia.smugmug.com/AstroPix/i-KK3p7wQ/A

As mentioned, here's an example of what I get with the "double-mirror" effect when using a highly reflective narrow-band filter.
robonrome avatar
robonrome avatar
Geoff:
It’s not normal. Could be dew on the optics or high thin cloud.

thanks Geoff, I think I can pretty well rule out dew... I run two dew bands one main tube behind dewshield and on dewshield for good measure and check regularly these are working well. High thin cloud is a possibility I need to consider.
robonrome avatar
robonrome avatar
Dave Rust:
I get a similar effect with filters with a mirror-like diaelectric coating.  On my rig, it's essentially an infinity reflection between the filter and the glass IR plate in front of the sensor.  The result looks like a sphere.

thanks Dave and again for the example you posted. i suspect what I have is a little different, not as hard as the halo you are seeing - I probably need to go back and look at more images from earlier sessions to try and see if this is a more constant effect that I'd expect if were filter or the flatenner etc.
robonrome avatar
robonrome avatar
Dale Penkala:
1st thing I go to when I see this is what @Geoff has already mentioned. Dew or a hazy high thin clouds causing issues.

But if you want to see if its your corrector I’d shoot an image with and without the flattener and compare to 2 images. That way your seeing the results of the change in a very short period of time to make a decision.
I also agree with you in the sense you want to get this figured out before investing the time in the image you want to go after!

Dale

thanks Dale, i do need to do some more comparisons... I hope it is just high cloud/haze ... but I definitely have noticed that stars seem a lot more defined/less diffuse when using my reducer compared to the straight flatenner as here which made me wonder, but though that might be a FL effect as well (e.g. star light dropping across more pixels)?
robonrome avatar
robonrome avatar
andrea tasselli:
Normally I get this kind of glow around bright stars with thin clouds and/or hazy conditions, most likely when the object is low on the horizon. As I use heater bands all the time dew collection on the lens isn't an explanation. And I don't use filters either.

thanks Andrea. Sounds like thin/high cloud or haze may be a factor. Like you I am pretty fastidious about dew control and am pretty sure that's not a factor here.
robonrome avatar
robonrome avatar
Thanks to comments above I went back and started looking at all my recent images and noticed I've been getting these sort of stars for a while to varying degrees even with reducer etc. 

This has led me to something of an epiphany...I suspect now that in some part or large part it is resulting from or being exacerbated by my current processing work flow. Below are two 300% extracts... immediately below is simple RGB combined after creating SHO channel stacks in APP.... then below this is the exact same areas after my typical work flow processing in another tool. I suspect this is user error on my part with that tool and perhaps overstretching for nebulosity... a good case  maybe for an approach that strips out stars before going to town on the data!



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