Secondary mirror coating issue or possible light leak problem?

Equipment Reflectors Help Needed Troubleshooting
7 replies•117 views
Anthony Grillo avatar
Anthony Grillo avatar

I was considering sending my secondary for my ago idk 14.5" over to terry at ostahowski optics for a recoat because if I look closely enough, I have what looks like an oil spot or something that slightly dulled a small part of my secondary coating that did not come off after cleaning. After further inspection of the mirror and some of the old subs of the issue I was having after I set it up to test, after it sat for a little, I'm coming to the conclusion this issue may be due to something else like a light leak possibly??

this is not dew or high cloud as it was the same night after night for a few nights and I was using a custom adapter I had made to mount a focuser which i was thinking may have not been painted fully and caused a reflection or had a leak possibly??

Before I send the mirror though,📷 3190agtestresize.png3190agtestresize.png I was wondering if I could get some further insight on what everyone else thought.

always shows up in the same position as dew or something but it is for sure not after some other testing

Brian Puhl avatar
Brian Puhl avatar

Have you tried stacking without flats? I’d like to see that ruled out first.

Well Written
Dark Matters Astrophotography avatar
Dark Matters Astrophotography avatar

Anthony Grillo · Nov 3, 2025 at 02:17 AM

I was considering sending my secondary for my ago idk 14.5" over to terry at ostahowski optics for a recoat because if I look closely enough, I have what looks like an oil spot or something that slightly dulled a small part of my secondary coating that did not come off after cleaning. After further inspection of the mirror and some of the old subs of the issue I was having after I set it up to test, after it sat for a little, I'm coming to the conclusion this issue may be due to something else like a light leak possibly??

this is not dew or high cloud as it was the same night after night for a few nights and I was using a custom adapter I had made to mount a focuser which i was thinking may have not been painted fully and caused a reflection or had a leak possibly??

Before I send the mirror though,📷 3190agtestresize.png3190agtestresize.png I was wondering if I could get some further insight on what everyone else thought.

always shows up in the same position as dew or something but it is for sure not after some other testing

Can you highlight the problem you are trying to solve? I do not see one.

Well Written
andrea tasselli avatar
andrea tasselli avatar
I have one mirror which actually has some small areas where the coating has flaked off and you'll be none the wiser by looking at the images produced. So I very much doubt you can see a dulling of the coatings either. Not that I see anything wrong with the image posted.
Concise
Anthony Grillo avatar
Anthony Grillo avatar

andrea tasselli · Nov 3, 2025, 09:51 AM

I have one mirror which actually has some small areas where the coating has flaked off and you'll be none the wiser by looking at the images produced. So I very much doubt you can see a dulling of the coatings either. Not that I see anything wrong with the image posted.

It’s the bright gradient from top left to center, that gradient was not there before I took the scope off of the mount and cleaned the mirrors and put that custom adapter I machined on. It’s in each individual sub and I can clearly see it as the images come through.

There is a clearly visible “spot” on my secondary that could not come off from cleaning so I initially thought it may have been that but the more I thought about it the more I doubted it being the issue.

Anthony Grillo avatar
Anthony Grillo avatar

Dark Matters Astrophotography · Nov 3, 2025, 06:26 AM

Anthony Grillo · Nov 3, 2025 at 02:17 AM

I was considering sending my secondary for my ago idk 14.5" over to terry at ostahowski optics for a recoat because if I look closely enough, I have what looks like an oil spot or something that slightly dulled a small part of my secondary coating that did not come off after cleaning. After further inspection of the mirror and some of the old subs of the issue I was having after I set it up to test, after it sat for a little, I'm coming to the conclusion this issue may be due to something else like a light leak possibly??

this is not dew or high cloud as it was the same night after night for a few nights and I was using a custom adapter I had made to mount a focuser which i was thinking may have not been painted fully and caused a reflection or had a leak possibly??

Before I send the mirror though,📷 3190agtestresize.png3190agtestresize.png I was wondering if I could get some further insight on what everyone else thought.

always shows up in the same position as dew or something but it is for sure not after some other testing

Can you highlight the problem you are trying to solve? I do not see one.

Bright gradient from top left to the middle, before I took the scope off of the mount, cleaned and installed that custom adapter I machined my field was flat and evenly illuminated with no visible gradients

John Hayes avatar
John Hayes avatar

How well is flat calibration working? That’s the best way to tell if you’ve got a stray light problem for this type of gradient.

John

andrea tasselli avatar
andrea tasselli avatar
Anthony Grillo:
It’s the bright gradient from top left to center, that gradient was not there before I took the scope off of the mount and cleaned the mirrors and put that custom adapter I machined on. It’s in each individual sub and I can clearly see it as the images come through.

There is a clearly visible “spot” on my secondary that could not come off from cleaning so I initially thought it may have been that but the more I thought about it the more I doubted it being the issue.


I assume you mean the minor brightening of the top left corner with respect to the opposite corner. If it is stray light or a light leak you should readily see it in the flattened images, as light leaks don't correct with flats. Does it?
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