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5nm Chroma Halos: Are these from the filters?

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#1 CosmicArk

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Posted 27 January 2022 - 10:36 AM

Hello everyone, 

 

I recently purchased some 5nm, 36mm Chromas for my Edge HD 9.25 and ZWO 294MM Pro. I replaced my ZWO's because I thought there would be no halos with the Chromas, but alas, here they are. SII seems to have the worse ones, with OIII having a faint one and Ha having none, The bright star in this image is a Mag 6 I believe, so no something crazy like Alnitak. 

 

I know there is an equation to calculate where in the imaging train the halo comes from using some math, but I dont know the equation. This is around 11 hours of data per filter. 

 

Here is S2 (Halo around star and on the left):

 

get.jpg?insecure

 

Here is OIII (just in the lower left):

 

get.jpg?insecure



#2 ChrisWhite

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Posted 27 January 2022 - 12:11 PM

What orientation is your filters?  The mirror side needs to face the camera for most people.

 

Regardless of how you have them installed, the easiest thing to test is simply to flip the filters. 


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#3 santafe retiree

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Posted 27 January 2022 - 12:50 PM

+1 on the filter flip -- Chroma says it does not make a difference which side faces the sensor but it did for me - I am in the middle of a multi night mosaic run so I don't want to mess with my imaging train right now so I can't say which side is up but as Chris said, easy enough to swap for a test -- Good luck.



#4 CosmicArk

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Posted 27 January 2022 - 01:39 PM

What orientation is your filters?  The mirror side needs to face the camera for most people.

 

Regardless of how you have them installed, the easiest thing to test is simply to flip the filters. 

 

 

+1 on the filter flip -- Chroma says it does not make a difference which side faces the sensor but it did for me - I am in the middle of a multi night mosaic run so I don't want to mess with my imaging train right now so I can't say which side is up but as Chris said, easy enough to swap for a test -- Good luck.

Interesting, I spoke with Chroma and they said it didnt matter, but doing research it seems that it might! I need to flip them and go take on Alnitak as a test to make sure I have them right, assuming that these halos are from them. 



#5 freestar8n

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Posted 27 January 2022 - 03:59 PM

Interesting, I spoke with Chroma and they said it didnt matter, but doing research it seems that it might! I need to flip them and go take on Alnitak as a test to make sure I have them right, assuming that these halos are from them. 

I haven't seen an actual imaging example where someone reversed the orientation and it made a difference - *except* a case where there was a light leak in one direction.

 

So you will definitely see people claiming it matters - for various reasons - but I don't know of any examples.

 

If anyone has an example I'd be interested to see it.

 

Frank



#6 ChrisWhite

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Posted 27 January 2022 - 04:06 PM

I haven't seen an actual imaging example where someone reversed the orientation and it made a difference - *except* a case where there was a light leak in one direction.

 

So you will definitely see people claiming it matters - for various reasons - but I don't know of any examples.

 

If anyone has an example I'd be interested to see it.

 

Frank

Here are a few anecdotes where filter orientation made a difference:

 

https://www.cloudyni...ection-problem/

 

https://www.cloudyni...ion/?p=10423985

 

https://www.cloudyni...ilter-artifact/

 

I have seen a few posts where there were reflections as seen in the OP here but I didnt find them on a 2 second google search.


Edited by ChrisWhite, 27 January 2022 - 04:07 PM.


#7 freestar8n

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Posted 27 January 2022 - 04:13 PM

Here are a few anecdotes where filter orientation made a difference:

 

https://www.cloudyni...ection-problem/

 

https://www.cloudyni...ion/?p=10423985

 

https://www.cloudyni...ilter-artifact/

 

I have seen a few posts where there were reflections as seen in the OP here but I didnt find them on a 2 second google search.

Ugh - those all appear to be due to light leak and not which side the reflection faces.  I had heard the same with ZWO filters but I think it was fixed.  And I guess it was a problem with earlier Baader filters.

 

If the filters are designed so they end up with a light leak one way and not the other - there is no reason it should be associated with which side is shiny.  It could happen either way - but if made well it won't happen either way.

 

I hope the chroma filters don't have those problems anymore.

 

A more healthy example would be to show actual halos around stars in one orientation - and none the other way.  A light leak wouldn't make that happen - and I would be surprised if there is such an example.

 

Frank



#8 ChrisWhite

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Posted 27 January 2022 - 04:17 PM

Ugh - those all appear to be due to light leak and not which side the reflection faces.  I had heard the same with ZWO filters but I think it was fixed.  And I guess it was a problem with earlier Baader filters.

 

If the filters are designed so they end up with a light leak one way and not the other - there is no reason it should be associated with which side is shiny.  It could happen either way - but if made well it won't happen either way.

 

I hope the chroma filters don't have those problems anymore.

 

A more healthy example would be to show actual halos around stars in one orientation - and none the other way.  A light leak wouldn't make that happen - and I would be surprised if there is such an example.

 

Frank

Good question. A while back I had a reflection issue where light was bouncing off the filters back up to the curved element of the reducer and back to the chip.  Scott from starizona modeled the problem.  I was using mounted filters so I couldnt flip them but I could see that depending on where reflections are happening and how they interact with the filters it could make a difference with respect to which side the AR coating is oriented. 

 

Chroma even tells users to try flipping the filters if there is a reflection problem, as a first test.  In any event, its an easy thing to try with nothing to lose.



#9 CosmicArk

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Posted 27 January 2022 - 05:37 PM

Ugh - those all appear to be due to light leak and not which side the reflection faces.  I had heard the same with ZWO filters but I think it was fixed.  And I guess it was a problem with earlier Baader filters.

 

If the filters are designed so they end up with a light leak one way and not the other - there is no reason it should be associated with which side is shiny.  It could happen either way - but if made well it won't happen either way.

 

I hope the chroma filters don't have those problems anymore.

 

A more healthy example would be to show actual halos around stars in one orientation - and none the other way.  A light leak wouldn't make that happen - and I would be surprised if there is such an example.

 

Frank

 

 

Good question. A while back I had a reflection issue where light was bouncing off the filters back up to the curved element of the reducer and back to the chip.  Scott from starizona modeled the problem.  I was using mounted filters so I couldnt flip them but I could see that depending on where reflections are happening and how they interact with the filters it could make a difference with respect to which side the AR coating is oriented. 

 

Chroma even tells users to try flipping the filters if there is a reflection problem, as a first test.  In any event, its an easy thing to try with nothing to lose.

Frank is right, none of those are from filters but light leaks. The math on a halo that size shows it not the filter. Using my pixel size, focal length, and all that, I get a distance of 18mm from the sensor, which is where the filters are. 

 

I am curious if flipping solves this because the halos are 800 pixels wide and lines up exactly with the math. 



#10 freestar8n

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Posted 27 January 2022 - 06:27 PM

Frank is right, none of those are from filters but light leaks. The math on a halo that size shows it not the filter. Using my pixel size, focal length, and all that, I get a distance of 18mm from the sensor, which is where the filters are. 

 

I am curious if flipping solves this because the halos are 800 pixels wide and lines up exactly with the math. 

Thanks.  The main thing is - there are very good reasons one way *could* be better than the other - but only if the outer edge isn't masked properly and actual white light is getting through.  That has nothing to do with one side being reflective - it has to do with a converging beam being able to get through one way and not another because of poor masking.

 

And this wouldn't show as halos in one case and none in the other - it would show as weird glows in the image, which those examples do show.

 

People have a sense that the reflective side matters - but there is no good optical basis for thinking that - and I don't know of examples that show the effect in the behavior of halos.

 

Frank



#11 CosmicArk

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Posted 27 January 2022 - 06:29 PM

Thanks.  The main thing is - there are very good reasons one way *could* be better than the other - but only if the outer edge isn't masked properly and actual white light is getting through.  That has nothing to do with one side being reflective - it has to do with a converging beam being able to get through one way and not another because of poor masking.

 

And this wouldn't show as halos in one case and none in the other - it would show as weird glows in the image, which those examples do show.

 

People have a sense that the reflective side matters - but there is no good optical basis for thinking that - and I don't know of examples that show the effect in the behavior of halos.

 

Frank

Frank,

 

so the math does show that the halos in my image do come directly from the filter, and the halos in my image are just that, halos and not light leaks. Do you think I have a defective filter? 



#12 freestar8n

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Posted 27 January 2022 - 06:41 PM

Frank,

 

so the math does show that the halos in my image do come directly from the filter, and the halos in my image are just that, halos and not light leaks. Do you think I have a defective filter? 

Hi.  I hadn't seen the full res. images.  You are talking about the large and faint ghost reflections on the left side of the image?  I think they are too large to be due to bounces within the filter.  Can you show the math you used?

 

When the halo is not on top of the star it is likely due to an air gap between two surfaces in the imaging train.  And since it involves light that made it through the filter, there is no reason to think the filter shiny side played a role.

 

It's possible the filter or some other surface is not well AR coated but I would need to do math on the halo size.

 

Frank



#13 CosmicArk

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Posted 27 January 2022 - 09:32 PM



Hi.  I hadn't seen the full res. images.  You are talking about the large and faint ghost reflections on the left side of the image?  I think they are too large to be due to bounces within the filter.  Can you show the math you used?

 

When the halo is not on top of the star it is likely due to an air gap between two surfaces in the imaging train.  And since it involves light that made it through the filter, there is no reason to think the filter shiny side played a role.

 

It's possible the filter or some other surface is not well AR coated but I would need to do math on the halo size.

 

Frank

Hey Frank,

 

I actually used a formula that you posted on a another thread of mine 2*t/(n*FNum) but I think I did the math wrong. So that should be 2 * 3000 / (1.5 * 10) = 400 um and with a pixel size on bin 2 of 4.6um, that should give a halo size of 87 pixels. This halo is actually 800 pixels wide. I dont know how to calculate the inverse of this to correlate the halo size to the distance because the other equation I tried is Distance = (Diameter * Pixel Size* FR)/1000 which gives 18.4 mm. But in the other thread you said this does not account for the right thing, but it is listed as CCD Filter Reflections.

 

What complicates things is that I noticed this on the SII. There are these little rings working their way out from the big halo as well. Maybe these are screw heads? 

 

get.jpg?insecure



#14 freestar8n

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Posted 28 January 2022 - 07:22 PM

Hey Frank,

 

I actually used a formula that you posted on a another thread of mine 2*t/(n*FNum) but I think I did the math wrong. So that should be 2 * 3000 / (1.5 * 10) = 400 um and with a pixel size on bin 2 of 4.6um, that should give a halo size of 87 pixels. This halo is actually 800 pixels wide. I dont know how to calculate the inverse of this to correlate the halo size to the distance because the other equation I tried is Distance = (Diameter * Pixel Size* FR)/1000 which gives 18.4 mm. But in the other thread you said this does not account for the right thing, but it is listed as CCD Filter Reflections.

 

What complicates things is that I noticed this on the SII. There are these little rings working their way out from the big halo as well. Maybe these are screw heads? 

 

 

Hi-

 

The small blobs are due to diffraction from the microlenses in the camera and are caused by the camera itself - so it's a separate issue.  You will see them around bright stars and there is nothing really to do about it.

 

If the diameter of the halo is D = 2*t/(n*FNum) then you also have t = nDFNum/2

 

For EdgeHD9.25 at f/10 and 800 pixels wide with 294 and 4.63 micron pixels I get an air gap (n=1) of 18.5mm.

 

Can you identify a gap of that size in your image train?

 

I see a halo on top of the bright star on the right - and also one on the left.  Are they the same size?  If not can you measure them carefully?

 

And you're not using a reducer - correct?

 

Frank



#15 CosmicArk

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Posted 28 January 2022 - 07:43 PM

Hi-

 

The small blobs are due to diffraction from the microlenses in the camera and are caused by the camera itself - so it's a separate issue.  You will see them around bright stars and there is nothing really to do about it.

 

If the diameter of the halo is D = 2*t/(n*FNum) then you also have t = nDFNum/2

 

For EdgeHD9.25 at f/10 and 800 pixels wide with 294 and 4.63 micron pixels I get an air gap (n=1) of 18.5mm.

 

Can you identify a gap of that size in your image train?

 

I see a halo on top of the bright star on the right - and also one on the left.  Are they the same size?  If not can you measure them carefully?

 

And you're not using a reducer - correct?

 

Frank

I did not know the 294 had microlensing! 

 

But measuring the halo more closely, the far left one seems to be 726 pixels and the one around the star is 654 pixels. So a little different. I do not have a reducer but the air gap seems to be around that number. The camera is 7.5mm and the filterwheel is 20mm so if the filter is near the middle, the math seems to line up. 



#16 Endymion

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Posted 28 January 2022 - 09:44 PM

I have the Chroma 3nm filters and did a lot of testing on my C11EDGEHD.  Orientation of the filters makes almost no difference with the microlens reflections.   With the AR side facing the camera and the filter side facing the OTA, the halos will be *slightly* bigger and dimmer.   The reflections are occurring between the microlens and the side of the filter with the filter coating.   Flipping the filter to a first order just changes the distance between the reflecting surfaces by the thickness of the filter glass.  

 

It is unclear to me whether the cause of the reflections off the filter surface is due to issues with the angle the reflected light hits the filter (changing the BW of the filter and thus causing reflections) or simply that the filters don't transmit perfectly and the amount not transmitted is simply reflected and not absorbed or that both causes can be in effect but it is definitely the filter surface and not the AR surface causing the reflections.   If you didn't have AR coating on the filter, things would get a lot worse since you would have two surfaces reflecting as was the case on my very old ZWO filter set which caused horrendous reflections.

 

As you increase the F ratio of the OTA the effect of the microlens reflection gets worse.  This is because the halo gets smaller in diameter and correspondingly brighter while the desired image gets dimmer.

 

At F10 I get very pronounced halos from Alnitak on O3 and S2 when shooting the horsehead/flame.   At F7 they get better but are still there.  If I could shoot at F4 I'm sure I wouldn't see them for this target.

 

There is just a limit to what the filters can achieve when trying to image faint targets with very bright stars around.  Unfortunately flipping the filters has almost no effect on the halos.



#17 deepanshu29

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Posted 28 January 2022 - 09:59 PM

I haven't seen an actual imaging example where someone reversed the orientation and it made a difference - *except* a case where there was a light leak in one direction.

 

So you will definitely see people claiming it matters - for various reasons - but I don't know of any examples.

 

If anyone has an example I'd be interested to see it.

 

Frank

I don't have any light leak in my system, here are two flats taken with 36mm 5nm Chroma Ha filters, one with light ring has mirrored side towards telescope, other one has towards camera. This light ring clearly shows up in star images as well. Ha and S2 filters both show this behavior but O3 does not. O3 is clean on either side. 

Mirrored side towards telescope - 

Screen Shot 2022-01-23 at 11.00.14 AM.jpg

 

Mirrored side towards camera sensor - 

 

Screen Shot 2022-01-23 at 4.13.54 PM.jpg



#18 ChrisWhite

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Posted 29 January 2022 - 10:12 AM

I did not know the 294 had microlensing! 

 

 

Not to be pedantic, but microlensing is not the correct terminology here.  Microlensing is a gravitational bending of light that can be found in the universe.  What you are seeing is a microlens diffraction pattern. 


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#19 freestar8n

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Posted 29 January 2022 - 05:19 PM

I don't have any light leak in my system, here are two flats taken with 36mm 5nm Chroma Ha filters, one with light ring has mirrored side towards telescope, other one has towards camera. This light ring clearly shows up in star images as well. Ha and S2 filters both show this behavior but O3 does not. O3 is clean on either side. 

Mirrored side towards telescope - 

 

 

Mirrored side towards camera sensor - 

 

 

What you're showing here is consistent with a light leak around the edges of the filter itself.  That is the one thing I have seen that can be direction-dependent in these filters.  It has nothing to do with which side is shiny - it just has to do with how exactly the outer edge of the filter is masked off.  Converging light can get through one way but not the other.  It doesn't show as halos around stars, but as weird large rings or blobs in the image.

 

Frank


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#20 deepanshu29

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Posted 31 January 2022 - 03:41 PM

What you're showing here is consistent with a light leak around the edges of the filter itself.  That is the one thing I have seen that can be direction-dependent in these filters.  It has nothing to do with which side is shiny - it just has to do with how exactly the outer edge of the filter is masked off.  Converging light can get through one way but not the other.  It doesn't show as halos around stars, but as weird large rings or blobs in the image.

 

Frank

Yeah that could be a possibility. I initially had 3D printed mask on these filters, but I was getting disc jamming because mine is an slim filter wheel, I ended up removing the mask, and holding the filters with just 3 screws and soft washers. 

I was merely sharing my experience regarding orientation of filters, yes, it has nothing to do with halos. I don't see halos in my images, it is just that one direction had annoying light ring which actually does not calibrate out with flats. 



#21 CosmicArk

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Posted 31 January 2022 - 10:40 PM

I just dont understand why others using the same filter and Edge scopes dont have a halo 



#22 hmaron

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Posted 01 February 2022 - 02:29 PM

Are we seeing the same thing? Certainly I see the smallish dense ring like effect around the bright star but that is actually more pronouncde in the OIII image. But then there is the big circle. But I see that paired to the left with it's donut like counterpart. I seen the same pair in the OIII image but rotated.
Are we referring to the same thing?
Certainly your concern is based on multiple images of other bright stars. But the larger ring that looks like a washer I would not suggest to be a halo particularly when I see its counterpart to the left (not on a star) and see the pair duplicated in the second image, albeit rotated, compared to the first.
Just curious if we are all analyzing this image as you. What I see looks reflection based.

 

 

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#23 CosmicArk

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Posted 01 February 2022 - 08:37 PM

Are we seeing the same thing? Certainly I see the smallish dense ring like effect around the bright star but that is actually more pronouncde in the OIII image. But then there is the big circle. But I see that paired to the left with it's donut like counterpart. I seen the same pair in the OIII image but rotated.
Are we referring to the same thing?
Certainly your concern is based on multiple images of other bright stars. But the larger ring that looks like a washer I would not suggest to be a halo particularly when I see its counterpart to the left (not on a star) and see the pair duplicated in the second image, albeit rotated, compared to the first.
Just curious if we are all analyzing this image as you. What I see looks reflection based.

I must say, I am quite confused at what you are meaning? 

 

There are halos in both images. In the OIII, there is no halo around the star, but there is one offset  from it. There is that weird pattern though. For the SII, there's two halos. One on the star, though slightly offset, and the other largely offset on the left. But these are of two completely different targets. 



#24 Lead_Weight

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Posted 01 February 2022 - 10:44 PM

I know exactly what those halos are. They're large scale micro lens reflections from the CMOS chip in the 294, and they tend to be more present in any system with a secondary, though I have seen the reflections in my refractor. There was a big thread on this at some point around the ASI6200 by Rockstarbill, but the conclusion was that some halos are unavoidable in compound systems where they are exacerbated.

 

You can just barely make them out here in this shot with my Esprit 100, they're on the left and right side of the image on either side of the star towards the edge of the frame.

 

get.jpg?insecure


Edited by Lead_Weight, 01 February 2022 - 10:55 PM.


#25 hmaron

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Posted 02 February 2022 - 12:19 PM

I must say, I am quite confused at what you are meaning? 

 

There are halos in both images. In the OIII, there is no halo around the star, but there is one offset  from it. There is that weird pattern though. For the SII, there's two halos. One on the star, though slightly offset, and the other largely offset on the left. But these are of two completely different targets. 

I just wanted to be certain what you were referring to because I see other things also. So just to clarify that I am not on LSD (at the moment) I thought I'd highlight exactly what I see in addition.  Do you see that "donut" I pulled from your SII image? Well, the identical "effect" also surrounds the star in that I image so I was wondering if you were referring to it as well. And, I see the same thing in the OIII, one on the star (very subtle) and one off the star in left bottom. So I see the pair in both

 

There is plenty to worry about in AP without worrying about something only a weirdo can see.

Sorry about my psychodelic vision. 

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Edited by hmaron, 02 February 2022 - 12:22 PM.

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