16 replies to this topic

[josephjja]

So in the attached image is Aldebaran as the big start. To the left of that is what I am guessing is another star, but looks like totally out of focus. 

The original image, Aldebaran is dead center, but had to crop to upload here for size.  It shows up in the lights, but not in the flats.  If this were a reflector and it was all the stars, I would say out of focus.  

Has anyone seen this before, where 1 star is out of focus but the rest are in?  It is a refractor.  It is also recent.

Attached Thumbnails

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[StargazerLuigi]

I think it's a reflection of Aldebaran, but the reflection is what an out of focus star looks like. What is your imaging train? Are you using a field flattener/reducer, filters?

Edited by StargazerLuigi, 06 December 2024 - 01:42 PM.

[Keith Rivich]

Reflection.

[sharkmelley]

You're in the DSLR forum, so are you using a DSLR with a full spectrum modification?  If so, you need to be using an IR/UV blocking filter.

[josephjja]

You're in the DSLR forum, so are you using a DSLR with a full spectrum modification?  If so, you need to be using an IR/UV blocking filter.

It is a dedicated CCD, ZWO ASI533mc Pro.  I didn't see a forum for CCDs? Not the right place?

 

I think it's a reflection of Aldebaran, but the reflection is what an out of focus star looks like. What is your imaging train? Are you using a field flattener/reducer, filters?

Astro-tech AT60ED + AT60FF (field flattener) + spacers to achieve 54.8mm backfocus + ASI533mc Pro

I guess I have to try another scope and without FF and pray it is not in the camera itself  

[RichA]

It is a dedicated CCD, ZWO ASI533mc Pro.  I didn't see a forum for CCDs? Not the right place?

 

Astro-tech AT60ED + AT60FF (field flattener) + spacers to achieve 54.8mm backfocus + ASI533mc Pro

I guess I have to try another scope and without FF and pray it is not in the camera itself  

Do a test, just factor out the flattener, take a shot without it, with an adjusted exposure time to get the same brightness and see if it recurs.  If it's still there, it could be the cover glass in front of the sensor.  Make sure the star is in the same part of the field.  But given the star is VERY overexposed, it's not really that big a surprise.

[ngc7319_20]

Yes, reflection of Aldebaran. It is out of focus, because the reflection light path is longer than the "normal" path.  For example, reflection off rear surface of flattener, traveling backwards to front surface of flattener, and then reflected again forward to sensor.  Also curved glass surfaces will change the focal distance of the reflection.  The protective window on the camera can also make reflections.  As a test, just take an image without a bright star in the field.

[deSitter]

So in the attached image is Aldebaran as the big start. To the left of that is what I am guessing is another star, but looks like totally out of focus. 

The original image, Aldebaran is dead center, but had to crop to upload here for size.  It shows up in the lights, but not in the flats.  If this were a reflector and it was all the stars, I would say out of focus.  

Has anyone seen this before, where 1 star is out of focus but the rest are in?  It is a refractor.  It is also recent.

What is crazy here is the halo around the halo. Yes double bounce reflections and out of focus, but what's up with the concentric ternary image?

 

-drl

[josephjja]

Yes, reflection of Aldebaran. It is out of focus, because the reflection light path is longer than the "normal" path.  For example, reflection off rear surface of flattener, traveling backwards to front surface of flattener, and then reflected again forward to sensor.  Also curved glass surfaces will change the focal distance of the reflection.  The protective window on the camera can also make reflections.  As a test, just take an image without a bright star in the field.

I imaged M35 last night and did not see this in M35, same exposure (60s) and everything.  I imaged M45 the other 2 nights and saw a weird artifact in M45, but doing 180s. Not sure how 1 object can be out of focus when everything else is in focus?  

[josephjja]

What is crazy here is the halo around the halo. Yes double bounce reflections and out of focus, but what's up with the concentric ternary image?

 

-drl

Using an autofocuser, so how would this be out of focus?  My M35 looks in focus afaict. I guess I have a night of playing with what in the optical chain is causing the reflections :/ 

[ngc7319_20]

... Not sure how 1 object can be out of focus when everything else is in focus?  

Aldebaran is the only thing in the image bright enough where you can see the reflection.  The reflection is out of focus due to extra light path, and possibly curved surfaces which are making the reflection.

[RichA]

What is crazy here is the halo around the halo. Yes double bounce reflections and out of focus, but what's up with the concentric ternary image?

 

-drl

It's a mild reflection of a very bright source so it's likely the main image is structured like the reflection (halo within halo) but you can't tell because the whole thing has bloomed into one big bright source.

[ngc7319_20]

Another thought regards the color of Aldebaran.  It is very red, and will have a lot of IR light.  Sometimes anti-reflection coatings work ok in the visible, but will reflect IR light.  I don't think this camera has a built-in IR blocking filter?  You might want to add a UV/IR blocking filter.  There is some chance that will make the reflection go away, or reduce it, if it is dominated by IR light.

[sharkmelley]

It is a dedicated CCD, ZWO ASI533mc Pro. 

The same applies - you need to be using an IR/UV blocking filter.  Most of those artefacts look like IR.

[josephjja]

Weird I did not get his in M35, or when I did Sadr or some other bright stars.  Could something on a lens cause this? Like a scratch, chip, or none dust object ( no idea what else ) or purely something in the optical chain is out of alignment?

[ngc7319_20]

Weird I did not get his in M35, or when I did Sadr or some other bright stars.  Could something on a lens cause this? Like a scratch, chip, or none dust object ( no idea what else ) or purely something in the optical chain is out of alignment?

 

M35 is not a bright red star.    Sadr is mag 2.3, yellow star.  Aldebaran is mag 1.0 orange - red star -- it has much more IR light.

 

Reflection also will depend on where the star is in the field of view -- especially if reflection is in the field flattener with curved surfaces.  You said Aldebaran was dead center.  Where were the other stars?  I guess it would be interesting to take more pics of Aldebaran, and move it around the field-of-view.

 

And again, try a UV / IR blocking filter.  Or don't put bright red stars at the field center.

 

I think chance of it being scratch or chip is near zero.  These would scatter light everywhere.  The diffraction rings in the reflection show that is well-collimated light beam -- just not in focus.

[josephjja]

Ok, looks like the reflection is in the field flattener.  It must have gotten banged up or something as it didn't used to do this, and it seems recent. I need to figure out how to put an IR filter in the path and keep the back focus, and try that. Saw same reflection on the Pleiades and they are magnitude about 3-4 ish and it was in same spot.