Weird Artifacts in Many of my Subframes

[Mike Lewis]

(I have already posted this on Cloudy Nights, but with such an active and accomplished group of astroimagers now here on FocalWorld I thought I would repost here, in case someone has some thoughts...)

So I am just getting back imaging with a new camera/filterwheel combo, and have been seeing some strange artifacts in many of my subframes. I am thinking it might be some internal reflection issues, but I am not sure. It seems to have a bit of a strange interrelationship with various areas I might be pointing, although I really do not have enough data yet to fully establish that.

The Setup:

• OTA – Stellarvue SVQ100 refractor, 580mm @ f/5.8, used previously with no apparent issues with an ASI1600 mono setup
• Camera – QHY268M-PH
• Filterwheel – QHYCFW3L
• Filters – Antlia Pro 3nm NB and version V LRGB filters, 2 inch mounted (thread in)

I have lots of data taken over the past couple of years with this same scope using an ASI1600 mono with Astrodon 31mm unmounted filters in a ZWO filter wheel. My setup is remotely located at a friend’s house in southern AZ and I control it from here in CO, so I do not have the easiest time troubleshooting things. Based on the issues I am about to show the camera/filterwheel combo is slated to come back here to CO over the holidays.

The Problem:

I am getting weird bright areas in many images (not all of them) with many of my filters, including the NB ones. It varies from a subtle loss of contrast in a specific area to an almost full wipeout of the image, and from covering a diffuse portion of the lower part of the sensor, to a well defined hot spot. All examples shown here shot with Ha filter, but I think this is happening with other filters as well (still trying to characterize…)

Examples (Mostly Sh2-171 data):

A ‘good’ subframe:

Diffuse Artifact:

Full Wipeout of Contrast:

Spot Artifact (taken on a different part of sky another night in the worst offending orientation it seemed like)

This seems to be very repeatable in a certain direction, but I think it is present in many of my subframes even those that are not pointing in this ‘worst’ direction.

I have noticed that the QHY filterwheel is shiny black anodize inside, which I could imagine would be prone to reflections, and the spot image seems to show some ‘texture’ in it. While the directionality relationship seems to speak more to LP, I do not think I have seen much LP in the past at least with my old setup using the Astrodon 5nm Ha filter, and to me these effects just don’t look like light pollution to me as they seem to have too much definition.

Questions:

• Has anyone experienced anything like this before?
• Has anyone had issues with internal reflections with a QHYCFW3 filter wheel?
• Has anyone seen this type of behavior using Antlia Pro filters?

Appreciate any thoughts or feedback as I try to figure out how to solve this issue.

Thanks bunches,



ML

 

[JimFox]

Hey Mike, I can see now what you were talking about.

You said it's repeatable in a certain direction, what direction is that? Does it need to have a bright star or planet in the vicinity?

Have you tried it without any filters? Or does it do it with all of your filters?

Sorry if I asked a question you answered already.

 

[JimFox]

Btw, do you have a small scope up here that you can test it with? Or an adapter so you can use one of your photography lenses with it?

You should be able to test it using your Polaris?

 

[Mike Lewis]

Thanks for the replies. Here are a few answers to questions:

- I have to go back now and really try to characterize it as far as other filters and portions of the sky. I think I am seeing this in other filters and in various parts of the sky but have mostly looked at the Hα filter and then mostly in a certain area of the sky. The worst offending direction is at about 30 degrees elevation and at about 350 degrees of Azimuth, from my friend's backyard in Green Valley, AZ. That does look out to where some LP could be, but again, to my eye, this just does not look diffuse enough to be LP.
- In that direction I have seen this on different nights at vastly different times of the night, so that would seem to imply it is not one specific object in the FOV
- My Polaris is up here in CO atm, so cannot really test much with that as far as this issue is concerned.
- This is somewhat complicated by the fact that there were dew issues at least a couple of the nights I was taking data, that could certainly affect what was being seen.

The camera / filterwheel is coming back to CO over the holidays and I will be trying to flat black paint the inside of it. That will then at least remove that issue from the troubleshooting trade space, assuming I can execute that without destroying anything.

ML

 

[JimFox]

Thanks for the update, could it be a light Leak in the optical train?

 

[chuckp]

Hi Mike, I doubt if it's light pollution, if you can see what I deal with and have no problems like that. Looks like a light leak or camera fogging. Maybe a loose connection and when you go to different areas of the sky you get a different light leak. Hope you get it straightened out when you get the camera in Co.