Topics

Reflections Nightmare - I'm ready to give up the hobby!


Jon
 
Edited

I have posted previously about reflections with a Riccardi reducer but now have the same issue with a native flattener and I have tried everything I can think off. 

My objective is to purchase a QUADTCC to replace the Riccardi but I cant do this until I sort out the existing reflections which I now suspect are coming from the sensor/filters.

I have now spent over 20 imaging sessions since October trying to sort out the issue and it has become such a chore that I'm ready to give up the hobby - can anyone help? 

Equipment - CFF 135/926mm, QHY600L, Chroma LRGB and 3nm Ha/OIII/SII. 

I have tried reversing filters individually in all permutations, moved spacing from between Objective and Filters to between Filters and Sensor and its just balloon squeezing. One filter works, then another one doesn't. Lights work but flats don't or vice versa. Nothing I do seems to help.

I can take images with no bright stars ok but as soon as I try something like the Pleiades I have issues, I even had reflections on Polaris with the current configuration. 

These are the latest test images on Pleiades, one for each filter - all 120s subs. All have reflections.
https://www.dropbox.com/sh/gn2x15vu8hs1whn/AADquWhGxYyE_SvfevDrYyzKa?dl=0

Can these reflections be resolved or am I wasting my time?

I would be very grateful if anyone could help or work with me to try and sort this out.

Thanks
Jon


Konstantin von Poschinger
 

Hi,

most reflections came from the combination of reducer, flattner and the filter.

Grüsse

Konstantin


Konstantin v. Poschinger


Hammerichstr. 5
22605 Hamburg
040/8805747
0171/1983476

Am 13.02.2021 um 13:22 schrieb Jon <jonkelly999@...>:



[Edited Message Follows]

I have posted previously about reflections with a Riccardi reducer but now have the same issue with a native flattener and I have tried everything I can think off. 

My objective is to purchase a QUADTCC to replace the Riccardi but I cant do this until I sort out the existing reflections which I now suspect are coming from the sensor/filters.

I have now spent over 20 imaging sessions since October trying to sort out the issue and it has become such a chore that I'm ready to give up the hobby - can anyone help? 

Equipment - CFF 135/926mm, QHY600L, Chroma LRGB and 3nm Ha/OIII/SII. 

I have tried reversing filters individually in all permutations, moved spacing from between Objective and Filters to between Filters and Sensor and its just balloon squeezing. One filter works, then another one doesn't. Lights work but flats don't or vice versa. Nothing I do seems to help.

I can take images with no bright stars ok but as soon as I try something like the Pleiades I have issues, I even had reflections on Polaris with the current configuration. 

These are the latest test images on Pleiades, one for each filter - all 120s subs. All have reflections.
https://www.dropbox.com/sh/gn2x15vu8hs1whn/AADquWhGxYyE_SvfevDrYyzKa?dl=0

Can these reflections be resolved or am I wasting my time?

I would be very grateful if anyone could help or work with me to try and sort this out.

Thanks
Jon


Joel Short
 

Sorry to hear this is continuing for you Jon. Three questions:
1.  Have you tried not using any filters to see if the reflections are still present?
2.  Were the reflections always present with the CFF flattener, or did the reflections appear after some time using the flattener?
3.  Remind me what camera you are using?

If you are getting reflections with both the Riccardi reducer (as expected) and the CFF flattener (not expected) then I have my doubts getting the QUADTCC will solve the issue. 
The reflections are the same across filters, with varying degree of intensity.  They look odd to me.  There is some sort of double reflection going on.  The reflections have a bright inner part and then an offset dimmer part. I've dealt with lots of reflections with the Riccardi and it looked nothing like this (with the same scope, as you know).  

I'm wondering if there might be an issue with the sensor cover glass, or maybe even the scope collimation. I'm no expert though...
joel


Roland Christen
 

Hello,

I cannot be sure about our QuadTCC working with your scope to produce no reflections. However, i do know that our 130 field flattener will work and produce zero reflections. It has been designed with convex radii so that any light reflected from the filters will be dispersed toward the outside of the focal plane and not towards the middle.

here is a simple test that you can do to determine where the reflections originate. Take an image with your filters and no field flattener or telecompressor in the optical path. If you still see reflections, then it is caused by your filters. Filters like the Astrodon series, have a sharp cutoff of each color, so they will pass the principal color and reflect the ones outside their passband. The colors that are reflected back up toward the telecompressor will then be rejected if they are reflected back from the telecompressor down to the chip. They will not be able to pass thru the filter again. Other filters may have less steep cutoff, and thereby allow some of the reflected light to pass again thru the filter and produce halos or reflection artifacts.

I have used Astrodon filters in all of my cameras since many years now and have never seen reflections like the ones in your images. However, I know about your reflections because I did have multiple reflections from a set of less expensive filters.

As far as using our 130 Field Flattener, I can assure you that this will not produce reflections, even if your filters do not have a sharp cutoff. If you have been watching our group for some time, you may have seen images taken by Ignacio, a lot of them became APOD images, and you will see the contrast and zero reflections in all of his images. I worked with him years ago to produce just the right Flattener design geometry to eliminate even the slightest hint of reflections - Ignacio was extremely demanding that this optic works perfectly.

So, the solution might require both testing a different filter and a different field flattener. The problem is not coming from the main objective for sure. So try my suggestion of removing the field flattener first and see if the reflections go away. Then the solution might be either change the filters or change the field flattener or both for best results.

Rolando


-----Original Message-----
From: Jon <jonkelly999@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 6:08 am
Subject: [ap-ug] Reflections Nightmare - I'm ready to give up the hobby!

I have posted previously about reflections with a Riccardi reducer but now have the same issue with a native flattener and I have tried everything I can think off. 

My objective is to purchase a QUADTCC to replace the Riccardi but I cant do this until I sort out the existing reflections which I now suspect are coming from the sensor/filters.

I have now spent over 20 imaging sessions since October trying to sort out the issue and it has become such a chore that I'm ready to give up the hobby - can anyone help? 

Equipment - CFF 135/926mm, QHY600L, Chroma LRGB and 3nm Ha/OIII/SII. 

I have tried reversing filters individually in all permutations, moved spacing from between Objective and Filters to between Filters and Sensor and its just balloon squeezing. One filter works, then another one doesn't. Lights work but flats don't or vice versa. Nothing I do seems to help.

I can take images with no bright stars ok but as soon as I try something like the Pleiades I have issues. 

These are the latest test images on Pleiades, one for each filter - all 120s subs. All have reflections.
https://www.dropbox.com/sh/gn2x15vu8hs1whn/AADquWhGxYyE_SvfevDrYyzKa?dl=0

Can these reflections be resolved or am I wasting my time?

I would be very grateful if anyone could help or work with me to try and sort this out.

Thanks
Jon


Eric Claeys
 

Have you tried taking pictures without any filter?  I would think that would rule out the filters themselves.

I also had several reflections with M45 and my SBIG 16200 with Astrodon filters.  I was never able to figure it out, although I didn't spend much time on it since no other object gave me reflections. 

Eric


Jon
 

Hi Joel, 
I have tried so many different permutations I'm not sure - will have to go back to my notes. Most of my testing was with the Riccardi and I think with that I still had reflections with a filter removed. The only time I didn't get reflections was with my original SX814 CCD and cheap Baader filters - but it was a small chip. I got some reflections using a D750 DSLR with no filters.

I don't remember seeing reflections with the CFF flattener until I got the QHY600L and the Chroma filters. The Chroma filters were recommended by Catalin and are only a little cheaper than Astrodon, although that doesn't mean the performance is also similar.

I'm not looking for a QuadTCC to solve the reflections, I just need a faster solution than the F7 flattener for imaging. It's the current reflections that are stopping me from buying the Quad - no point adding another variable until I have solved the current problem :)

These reflections are probably the worst so far, since I moved the spacing. but yes they are odd. I'm no expert but wondering if the circular reflections are filter to sensor and the oval ones are from a curved surface.

I think collimation is probably ok from my CCDI results.


Jon
 

Thanks Roland, I will try that. 

Joel, who posted above, has the same scope and flattener as I have but uses the ZWO version of the camera and, I think, Astrodon filters and doesn't have the issue so I am wondering if its a camera/filter issue. 

Chroma tell me that their filters can be used in any orientation but I would be interested to know if you have a suggested starting point, as things stand they are in various orientations?


Jon
 

I will try removing a filter again. 
Unfortunately its not just M45, I got reflections two nights ago even on Polaris.


Joel Short
 

I use Chroma LRGB and Astrodon 5nm narrowband filters, and I see no reflections with the CFF flattener.  The M82 Riccardi reducer was a different story.  Basically, I noticed that the spacers inside the reducer were very reflective.  I 3D printed some small baffle rings that sit inside the metal spacers in the reducer.  The reflections were completely eliminated with the baffles in place.  The one drawback is that the clear aperture was reduced a little bit, but not enough to affect vignetting of the full frame sensor.
joel


On Sat, Feb 13, 2021 at 10:39 AM Jon <jonkelly999@...> wrote:
Thanks Roland, I will try that. 

Joel, who posted above, has the same scope and flattener as I have but uses the ZWO version of the camera and, I think, Astrodon filters and doesn't have the issue so I am wondering if its a camera/filter issue. 

Chroma tell me that their filters can be used in any orientation but I would be interested to know if you have a suggested starting point, as things stand they are in various orientations?
_._,_._,


Roland Christen
 


Chroma tell me that their filters can be used in any orientation but I would be interested to know if you have a suggested starting point, as things stand they are in various orientations?
You can flip filters all you want, but it won't change things. Remove the flattener and shoot straight thru. You won't get the funny ghosts but you may get halos around the bright stars.

Roland


-----Original Message-----
From: Jon <jonkelly999@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 10:39 am
Subject: Re: [ap-ug] Reflections Nightmare - I'm ready to give up the hobby!

Thanks Roland, I will try that. 

Joel, who posted above, has the same scope and flattener as I have but uses the ZWO version of the camera and, I think, Astrodon filters and doesn't have the issue so I am wondering if its a camera/filter issue. 

Chroma tell me that their filters can be used in any orientation but I would be interested to know if you have a suggested starting point, as things stand they are in various orientations?


Roland Christen
 


I will try removing a filter again. 
That won't prove anything unfortunately. You need to remove the Flattener.

Roland


-----Original Message-----
From: Jon <jonkelly999@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 10:42 am
Subject: Re: [ap-ug] Reflections Nightmare - I'm ready to give up the hobby!

I will try removing a filter again. 
Unfortunately its not just M45, I got reflections two nights ago even on Polaris.


Jon
 

On Sat, Feb 13, 2021 at 06:15 PM, Roland Christen wrote:
That won't prove anything unfortunately. You need to remove the Flattener.
Sorry, I meant I will remove the flattener and a couple of filters (Ha and Blue). If I get reflections where there are filters in place and no reflections where the filters are missing it should help narrow things down.


Jon
 

On Sat, Feb 13, 2021 at 06:14 PM, Roland Christen wrote:
You can flip filters all you want, but it won't change things.
I have found that flipping the filters does make a difference. I don't understand why but it was explained that the filters are 3mm thick and flipping them moves the reflective surface by 3mm. I also don't understand why changing spacing makes a difference but it does seem to. 

When I was optimising back focus I got to a point that my flats were working for some filters but when I added a final 0.6mm spacing my flats were suddenly swamped with ghosts as here. Odd that 0.6mm spacing made this happen.


Christopher Erickson
 

It might be possible to use trigonometry to determine the distance of the source of the reflection from the sensor. Take two pics of the same field with a shift of a precise amount of the field. Measure the position shift of the reflection.


-Christopher Erickson
Observatory engineer
Waikoloa, HI 96738
www.summitkinetics.com
   

On Sat, Feb 13, 2021, 10:56 AM Jon <jonkelly999@...> wrote:
On Sat, Feb 13, 2021 at 06:14 PM, Roland Christen wrote:
You can flip filters all you want, but it won't change things.
I have found that flipping the filters does make a difference. I don't understand why but it was explained that the filters are 3mm thick and flipping them moves the reflective surface by 3mm. I also don't understand why changing spacing makes a difference but it does seem to. 

When I was optimising back focus I got to a point that my flats were working for some filters but when I added a final 0.6mm spacing my flats were suddenly swamped with ghosts as here. Odd that 0.6mm spacing made this happen.


Roland Christen
 

Those multiple reflections are caused by the chip itself sending light back to the filter, and yes indeed, flipping the filter will cause them to appear and disappear or change size. That's because in one case the light does not go thru the filter and bounces right back off the first layer. When you flip the filter, that reflection goes thru the second layer (now the first layer) which then proceeds thru the filter and up out of the front of the scope.

In the case of these multiple reflections the field flattener/telecompressor is not involved at all. The tell-tale evenly spaced 3x3 reflections is an indication that the microlenses overlaying the sensor pixels are reflecting light back up to the filter. In some cameras the microlens layer is not multi-coated and can reflect 5% of the light back up.

Ghost images that appear opposite to a bright star that is not perfectly centered is an indication that the last lens element of a field flattener or telecompressor has a concave surface which re-images the reflected light from the sensor. This is a completely different form of reflection from the one you attached in this post.

Rolando

-----Original Message-----
From: Jon <jonkelly999@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 2:55 pm
Subject: Re: [ap-ug] Reflections Nightmare - I'm ready to give up the hobby!

On Sat, Feb 13, 2021 at 06:14 PM, Roland Christen wrote:
You can flip filters all you want, but it won't change things.
I have found that flipping the filters does make a difference. I don't understand why but it was explained that the filters are 3mm thick and flipping them moves the reflective surface by 3mm. I also don't understand why changing spacing makes a difference but it does seem to. 

When I was optimising back focus I got to a point that my flats were working for some filters but when I added a final 0.6mm spacing my flats were suddenly swamped with ghosts as here. Odd that 0.6mm spacing made this happen.


Roland Christen
 

You can measure the diameter of the halo and knowing the F-ratio you can calculate the distance from the chip. It must be a flat surface, and using the diameter in this image, it must be chip to filter and back to chip reflection. The multiple reflections come from the microlens layer above the pixels.

Rolando



-----Original Message-----
From: Christopher Erickson <christopher.k.erickson@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 3:08 pm
Subject: Re: [ap-ug] Reflections Nightmare - I'm ready to give up the hobby!

It might be possible to use trigonometry to determine the distance of the source of the reflection from the sensor. Take two pics of the same field with a shift of a precise amount of the field. Measure the position shift of the reflection.


-Christopher Erickson
Observatory engineer
Waikoloa, HI 96738
www.summitkinetics.com
   

On Sat, Feb 13, 2021, 10:56 AM Jon <jonkelly999@...> wrote:
On Sat, Feb 13, 2021 at 06:14 PM, Roland Christen wrote:
You can flip filters all you want, but it won't change things.
I have found that flipping the filters does make a difference. I don't understand why but it was explained that the filters are 3mm thick and flipping them moves the reflective surface by 3mm. I also don't understand why changing spacing makes a difference but it does seem to. 

When I was optimising back focus I got to a point that my flats were working for some filters but when I added a final 0.6mm spacing my flats were suddenly swamped with ghosts as here. Odd that 0.6mm spacing made this happen.


ROBERT WYNNE
 

This has to be one of the most informative exchanges since I joined the group. Thanks for the education. -Best, Robert

On 02/13/2021 1:14 PM Roland Christen via groups.io <chris1011@...> wrote:
 
 
Those multiple reflections are caused by the chip itself sending light back to the filter, and yes indeed, flipping the filter will cause them to appear and disappear or change size. That's because in one case the light does not go thru the filter and bounces right back off the first layer. When you flip the filter, that reflection goes thru the second layer (now the first layer) which then proceeds thru the filter and up out of the front of the scope.
 
In the case of these multiple reflections the field flattener/telecompressor is not involved at all. The tell-tale evenly spaced 3x3 reflections is an indication that the microlenses overlaying the sensor pixels are reflecting light back up to the filter. In some cameras the microlens layer is not multi-coated and can reflect 5% of the light back up.
 
Ghost images that appear opposite to a bright star that is not perfectly centered is an indication that the last lens element of a field flattener or telecompressor has a concave surface which re-images the reflected light from the sensor. This is a completely different form of reflection from the one you attached in this post.
 
Rolando
 
-----Original Message-----
From: Jon <jonkelly999@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 2:55 pm
Subject: Re: [ap-ug] Reflections Nightmare - I'm ready to give up the hobby!

On Sat, Feb 13, 2021 at 06:14 PM, Roland Christen wrote:
You can flip filters all you want, but it won't change things.
I have found that flipping the filters does make a difference. I don't understand why but it was explained that the filters are 3mm thick and flipping them moves the reflective surface by 3mm. I also don't understand why changing spacing makes a difference but it does seem to. 

When I was optimising back focus I got to a point that my flats were working for some filters but when I added a final 0.6mm spacing my flats were suddenly swamped with ghosts as here. Odd that 0.6mm spacing made this happen.


Roland Christen
 

I hope it is resolved, since it would be a shame if one of those new CMOS cameras was producing halos.

Rolando



-----Original Message-----
From: ROBERT WYNNE <robert-wynne@...>
To: main@ap-ug.groups.io; Roland Christen via groups.io <chris1011@...>
Sent: Sat, Feb 13, 2021 6:07 pm
Subject: Re: [ap-ug] Reflections Nightmare - I'm ready to give up the hobby!

This has to be one of the most informative exchanges since I joined the group. Thanks for the education. -Best, Robert
On 02/13/2021 1:14 PM Roland Christen via groups.io <chris1011@...> wrote:
 
 
Those multiple reflections are caused by the chip itself sending light back to the filter, and yes indeed, flipping the filter will cause them to appear and disappear or change size. That's because in one case the light does not go thru the filter and bounces right back off the first layer. When you flip the filter, that reflection goes thru the second layer (now the first layer) which then proceeds thru the filter and up out of the front of the scope.
 
In the case of these multiple reflections the field flattener/telecompressor is not involved at all. The tell-tale evenly spaced 3x3 reflections is an indication that the microlenses overlaying the sensor pixels are reflecting light back up to the filter. In some cameras the microlens layer is not multi-coated and can reflect 5% of the light back up.
 
Ghost images that appear opposite to a bright star that is not perfectly centered is an indication that the last lens element of a field flattener or telecompressor has a concave surface which re-images the reflected light from the sensor. This is a completely different form of reflection from the one you attached in this post.
 
Rolando
 
-----Original Message-----
From: Jon <jonkelly999@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 2:55 pm
Subject: Re: [ap-ug] Reflections Nightmare - I'm ready to give up the hobby!

On Sat, Feb 13, 2021 at 06:14 PM, Roland Christen wrote:
You can flip filters all you want, but it won't change things.
I have found that flipping the filters does make a difference. I don't understand why but it was explained that the filters are 3mm thick and flipping them moves the reflective surface by 3mm. I also don't understand why changing spacing makes a difference but it does seem to. 

When I was optimising back focus I got to a point that my flats were working for some filters but when I added a final 0.6mm spacing my flats were suddenly swamped with ghosts as here. Odd that 0.6mm spacing made this happen.


Bill Long
 

Super long thread here about the exact same issue:

https://www.cloudynights.com/topic/728648-reflection-artifacts-in-the-asi6200/

Issue was far worse on optics with a central obstruction. Somewhere in that thread is a script you can run in PixInsight to determine the location of the reflection. From looking at your images it is the filter.

The CMOS cameras tested were more prone to cause the problem, but CCD chips showed similar patterns as well. Changing filter brands to Astrodon didn't change anything. 


Khushrow Machhi
 

I upgraded to an ASI6200MM camera with an ATIK filter wheel last year.  I use this setup with my 130GTX with the field flattener and the QTCC, with 50mm Chroma LRGB and 3nm Ha, OIII and SII filters..  On first use I had major issues with reflections.  This was particularly easy to see when taking flats.  In my case it was an issue of light leakage around the filters and then then causing reflections that were especially noticeable with the NB filters.  Fortunately I had filter masks from ZWO and these had the same hole patterns as the ATIK fw and I used these, and they effectively blocked any light paths around the filters.  This resolved the leakage and subsequent reflection issues.

One issue I continue to observe is that flats with the Ha and SII filters has what appears to be uneven illumination (very subtle) across the frame.  I had not previously seen this when using CCDs and Astrodon 3nm NB filters.  So, when I saw this with the Chroma's I suspected something was the issue with these filters.  I contacted Chroma and they explained this as some sort of interference between the camera and the filters.  I think in this long chain there is an explanation by Roland that may explain what is happening here. Anyway, I decided to get an Astrodon 50mm 3nm Ha filter to check on the difference between Astrodon and Chroma, as the Chroma filters used to be about $400 cheaper.  Chroma has since raised their price to $1300 and are now more expensive than Astrodon's.  Anyway, I do see the same uneven illumination with the Astrodon Ha filter also in the flat frames and the pattern is the same as with the Chroma filters.  This effect is subtle and if I can find the flats I will post one showing what I see.  This does not affect my images as far as I can tell.  Additionally, as a comparison of the Chroma vs Astrodon 3nm Ha filter, when looking at the nebulosity details I cannot tell the difference between the two, however if there is a bright star in the image I see some reflection on the bright stars with the Astrodon that I do not see with the Chroma.  

Khushrow