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Old 29-05-2020, 02:50 PM
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Anyone seen this before?

Anyone seen this type of internal reflection / refraction before?? It's a 60sec exposure. The bright star is mag 4.8. Never seen it before.
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Old 29-05-2020, 02:54 PM
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Bright cylindrical edge somewhere bouncing back the light reflected by a filter or sensor.
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Old 29-05-2020, 03:00 PM
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Thanks Marc. That sounds plausible. I thought it might be a refraction off the filter edge (somehow) (??)
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Old 29-05-2020, 03:09 PM
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Quote:
Originally Posted by marc4darkskies View Post
Thanks Marc. That sounds plausible. I thought it might be a refraction off the filter edge (somehow) (??)
biro black your filter edges helps as well. in my case it was an adapter m42 with a bright anodized edge picking up off field bright stars.
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Old 29-05-2020, 03:10 PM
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I agree with Marc Frogginator and maybe a bright star just out of shot but not reflection looks like you can see a split ring
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Old 29-05-2020, 03:13 PM
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I agree with Marc Frogginator and maybe a bright star just out of shot but not reflection looks like you can see a split ring
No other bright stars nearby. I think Marc may be right - I'll pull the camera off and have a squiz. I'll also blacken the filter edges just in case.
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Old 29-05-2020, 03:35 PM
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I've seen this before with my scope, it turned outto be light reflecting off an internal wall that was black anodised, but not painted flat black or internally baffled. Some flat black paint fixed it up. Also it would be interesting to see if it had a rainbow type look if you combine the colour filter exposures. I think that would indicate refraction.


Josh
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Old 29-05-2020, 03:45 PM
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I've seen this before with my scope, it turned outto be light reflecting off an internal wall that was black anodised, but not painted flat black or internally baffled. Some flat black paint fixed it up. Also it would be interesting to see if it had a rainbow type look if you combine the colour filter exposures. I think that would indicate refraction.


Josh
Thanks for that Josh! Good point. Once I saw it though I aborted my session so no colour. If I can't remedy it with black paint I'll go in and do a short colour run.
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Old 30-05-2020, 08:51 AM
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Quote:
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I agree with Marc Frogginator and maybe a bright star just out of shot but not reflection looks like you can see a split ring
Quote:
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No other bright stars nearby. ....
Doh! There is actually a very bright star about 1 degree away so I'll need to look at baffling as well I think.
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Old 30-05-2020, 09:16 AM
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I used to see something similar on the CDK17. Planewave sent some 3D printed baffles for the corrector and around the central tube and it stopped them.

So if the filter does not work then I would suspect you need a baffle or two similar to the Planewave.

Greg.
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Old 30-05-2020, 10:37 PM
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I have seen something very similar. before.

Almost certain this is an internal baffle reflection.
located close to the back plate of the 'scope....probably off a black (but still shiny) anodised surface.

Nothing some matt black acrylic or flocking material ( honest... I am not cursing ) will not fix in a jiffy.
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Old 31-05-2020, 10:33 AM
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Quote:
Originally Posted by gregbradley View Post
I used to see something similar on the CDK17. Planewave sent some 3D printed baffles for the corrector and around the central tube and it stopped them.

So if the filter does not work then I would suspect you need a baffle or two similar to the Planewave.

Greg.
Quote:
Originally Posted by Peter Ward View Post
I have seen something very similar. before.

Almost certain this is an internal baffle reflection.
located close to the back plate of the 'scope....probably off a black (but still shiny) anodised surface.

Nothing some matt black acrylic or flocking material ( honest... I am not cursing ) will not fix in a jiffy.
Thanks Greg & Peter,

Done a lot of thinking about this! I'm pretty convinced now that my artefact coming from the Mag 1 star that's only 1 degree away from the imaged field. The arc's focal point is roughly indicating the position of that star. I THINK this means it is an extraneous light problem as opposed to an internal reflections.

I initially (2013) had severe problems with flaring almost all the time because they mounted a new design flattener further forward than usual. See the first image below - the red ray indicates the problem. They responded with a clever and novel primary baffle extension (See the pink component in the middle image below) which totally eliminated extraneous light impinging on the flattener lens. Alas, it had the side effect of adding glare around stars (bloating them) and raising the background level either by diffraction or grazing incidence of light from the primary on the "matt" surface of the extension (or both).

I experimented with adding my own baffle extensions to make the secondary baffle larger and the primary baffle a bit longer (both using flocking board). See the 3rd image below. I've been operating like this since 2014 without problems (beyond incleasing the obstruction and perhaps a tiny bit more vignetting.

So, as you can see from the 3rd image there is still the possibility of extraneous light hitting the edge of the flattener lens. I do have a home made matt black baffle ring down there, but it may not be sufficiently broad. I'm loathe to make it bigger though. Before I go taking the camera off and looking for shiny stuff I think I'll lengthen my primary baffle extension - I can just pull it out a bit.

Having said all that, a star only 1 degree away does suggest it's light is travelling down the whole optical path in which case it's a scattering / reflection problem from something in the imaging train = look for shiny things in the imaging train!

BTW Peter, I already have little cylinders of flocking board in the imaging train and close to the flattener. That doesn't mean I don't need more of course.
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Old 31-05-2020, 04:52 PM
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Glare from a bright star just outside the FOV is pretty much what I am talking about as well. The CDK would sometimes show that glare from these bright stars.

How the baffle is implemented and how wide it should be and where it goes is a matter for the manufacturer to advise really. I just know the CDK one worked quite well, so much that I ended up not installing one of them that was meant for the corrector (2 went there and I only installed 1).

Reflections are always possible but a neat arc like that? I got a reflection off an adapter when I used an AP reducer on my AP140. It looked like a spiral galaxy at an angle. That was from a reflective surface on an anodised part but it wasn't an arc nor anywhere near that large.

Greg.
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Old 01-06-2020, 10:17 AM
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Quote:
Originally Posted by marc4darkskies View Post
Anyone seen this type of internal reflection / refraction before?? It's a 60sec exposure. The bright star is mag 4.8. Never seen it before.

Sure have...


http://www.iceinspace.com.au/forum/s...2&postcount=31


I hope you can fix it easily on that scope.


Best,
EB
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Old 01-06-2020, 10:33 AM
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When I did the surgery on my C11 years ago as a result the tube got slightly longer. I used a small roll of 0.1mm stainless steel sheet and jammed it in the central baffle tube to extend it a little bit and painted it black matte. It's handy to quickly test as you can push it in or pull it out and check the results on the spot.
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Old 01-06-2020, 11:32 AM
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Sure have...


http://www.iceinspace.com.au/forum/s...2&postcount=31


I hope you can fix it easily on that scope.


Best,
EB
Thanks Eric. Interestingly, this is the first time since my mods back in 2014 that I've had a problem. I guess that's because I've never imaged so close to a Mag 1 star. Note that I imaged the Antennae without issue in 2016.

Quote:
Originally Posted by multiweb View Post
When I did the surgery on my C11 years ago as a result the tube got slightly longer. I used a small roll of 0.1mm stainless steel sheet and jammed it in the central baffle tube to extend it a little bit and painted it black matte. It's handy to quickly test as you can push it in or pull it out and check the results on the spot.
That's exactly what I did back in 2014 - see the third image in my post above (red shading). I used rolled up flocking board. I'll experiment by pulling it out a bit before I go adding more flocking or even matt paint inside my imaging train
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