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RASA 11 - problems with reflections/rainbows caused by bright stars

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#26 calypsob

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Posted 21 October 2022 - 09:54 AM

I've recently ran into this issue as well.  I've had my Octopi attached to my RASA 11 v2 for about a year.  I run the rig with an ASI6200MC camera as well.  

 

Not until about 2 weeks ago when I got serious about leveling the tilt of my camera via the Octopi did this 'rainbow glare' issue begin.  Before I got all four corners of the tilt adapter within 3-5 microns of each other was this 'effect' an issue.  My stars evened out with adjusting the tilt, but this glare effect started.  Ugh.  haha

 

I can get the flocking paper easily, but I'm concerned with cutting it accurately.  How did you guys cut it with precision?

 

 

PS. If anyone would care to sell me a 3D printed ring I'd be interested, but the one posted here is for an APS-C sensor and not a full frame, so I don't know if it'd even work.  I do not own a 3D printer.

It will take trial and error to get the size right.

I suggest a good circle cutter 

https://www.amazon.c...,aps,111&sr=8-3

 

and some adhesive light blocking felt

 

https://www.amazon.c..._images_section
 



#27 Fegato

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Posted 21 October 2022 - 09:57 AM

I've recently ran into this issue as well.  I've had my Octopi attached to my RASA 11 v2 for about a year.  I run the rig with an ASI6200MC camera as well.  

 

Not until about 2 weeks ago when I got serious about leveling the tilt of my camera via the Octopi did this 'rainbow glare' issue begin.  Before I got all four corners of the tilt adapter within 3-5 microns of each other was this 'effect' an issue.  My stars evened out with adjusting the tilt, but this glare effect started.  Ugh.  haha

 

I can get the flocking paper easily, but I'm concerned with cutting it accurately.  How did you guys cut it with precision?

 

 

PS. If anyone would care to sell me a 3D printed ring I'd be interested, but the one posted here is for an APS-C sensor and not a full frame, so I don't know if it'd even work.  I do not own a 3D printer.

I'm still using my 5mm ring of flocking paper. To be honest it's not really a "precision" job!  I used a protractor to get the right width and just cut it out with scissors!  I don't use the Celestron filter, so I took the glass out of the filter holder and then screwed the filter holder in to hold the flocking paper nicely in place.

 

This has worked perfectly, so I never did get the printed part that Pablo created above. I'm not sure about your light path comment - you need about 5mm to stop any problems with a full frame sensor (in my experience - and I think same for Daniel above).  Is the printed part a different width? (I can't tell from the description). 

 

In any case, you really need Flats with a full frame sensor, so hopefully they will sort out any other anomalies in the illumination of the sensor caused by this.



#28 calypsob

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Posted 21 October 2022 - 10:50 AM

I'm still using my 5mm ring of flocking paper. To be honest it's not really a "precision" job!  I used a protractor to get the right width and just cut it out with scissors!  I don't use the Celestron filter, so I took the glass out of the filter holder and then screwed the filter holder in to hold the flocking paper nicely in place.

 

This has worked perfectly, so I never did get the printed part that Pablo created above. I'm not sure about your light path comment - you need about 5mm to stop any problems with a full frame sensor (in my experience - and I think same for Daniel above).  Is the printed part a different width? (I can't tell from the description). 

 

In any case, you really need Flats with a full frame sensor, so hopefully they will sort out any other anomalies in the illumination of the sensor caused by this.

Sometimes I prefer flock honestly. It takes 20 minutes to measure and draw a part, then 4-9 hours to print not including failures, then you paint the part well and hope it has a good fit, prints shrink so there is always a degree of tolerance. 
I always leave open the option of painting and using stick on flock, it can come in very thin mediums which is great in a area where you could end up creating an aperture stop. The hole cutter is also invaluable, we work with alot of round flat surfaces that can reflect light in this side of the hobby. Definitely take time to explore and choose the most efficient options for the job.


Edited by calypsob, 21 October 2022 - 10:51 AM.

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#29 jcrop

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Posted 21 October 2022 - 11:39 AM

Sometimes I prefer flock honestly. It takes 20 minutes to measure and draw a part, then 4-9 hours to print not including failures, then you paint the part well and hope it has a good fit, prints shrink so there is always a degree of tolerance. 
I always leave open the option of painting and using stick on flock, it can come in very thin mediums which is great in a area where you could end up creating an aperture stop. The hole cutter is also invaluable, we work with alot of round flat surfaces that can reflect light in this side of the hobby. Definitely take time to explore and choose the most efficient options for the job.

 

Wes,

 

Right!  I wasn't looking forward to investing in a 3D printer and all the effort it takes to make the part, but kudos to those who do, honestly, they are talented.

 

Thanks for the links to a circle cutter and flocking paper.  I ordered the paper and cutter this morning.  I hope to be reflection free this Sunday if the weather stays as nice as it is down here in East Texas.  I'm surprised so many haven't had this issue.  I wonder if tilt is such a problem that it isn't an issue until the tilt is tuned up.  The reflections in mine didn't start until I tuned up the tilt, but that could be a coincidence.  I've had my RASA 2+ years and the Octopi for almost a year.  I tuned the Octopi up 2 weekends ago and then noticed the reflections.

Did you use only a single piece of flock paper?  Looking at the pics you posted in this thread it appears that way.  I want to make sure I'm not seeing that wrong.  Thank you so kindly and the others in this thread for showing me the way.  I appreciate it immensely.

 

Clears minds and clear skies.

 

-Jason


Edited by jcrop, 21 October 2022 - 11:58 AM.


#30 calypsob

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Posted 21 October 2022 - 12:57 PM

Wes,

 

Right!  I wasn't looking forward to investing in a 3D printer and all the effort it takes to make the part, but kudos to those who do, honestly, they are talented.

 

Thanks for the links to a circle cutter and flocking paper.  I ordered the paper and cutter this morning.  I hope to be reflection free this Sunday if the weather stays as nice as it is down here in East Texas.  I'm surprised so many haven't had this issue.  I wonder if tilt is such a problem that it isn't an issue until the tilt is tuned up.  The reflections in mine didn't start until I tuned up the tilt, but that could be a coincidence.  I've had my RASA 2+ years and the Octopi for almost a year.  I tuned the Octopi up 2 weekends ago and then noticed the reflections.

Did you use only a single piece of flock paper?  Looking at the pics you posted in this thread it appears that way.  I want to make sure I'm not seeing that wrong.  Thank you so kindly and the others in this thread for showing me the way.  I appreciate it immensely.

 

Clears minds and clear skies.

 

-Jason

I only needed 1 piece as you see in robins thread


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#31 jcrop

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Posted 21 October 2022 - 01:44 PM

Just to give you all an example of what I'm facing, here is a screenshot of the Witch Head IC 2118.

 

This wasn't an issue until after I tuned up my Octopi tilt adapter.  

Attached Thumbnails

  • Screen Shot 2022-10-21 at 13.30.11.png


#32 calypsob

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Posted 21 October 2022 - 02:30 PM

Just to give you all an example of what I'm facing, here is a screenshot of the Witch Head IC 2118.

 

This wasn't an issue until after I tuned up my Octopi tilt adapter.  

I suspect you are splitting rigel at the mirrors edge, thats a brutally bright star


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#33 jcrop

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Posted 21 October 2022 - 02:45 PM

I suspect you are splitting rigel at the mirrors edge, thats a brutally bright star

 

This panel is part of a 4 panel mosaic and yes Rigel is not far away.  In that panel, believe it or not, Rigel doesn't cause as much reflection.  This is the worst panel as a whole since Rigel is just off sensor.  And what I've learned about this reflection problem is the star light on the *edges* of the sensor are the main culprits when imaging, not stars directly captured onto the sensor.



#34 Fegato

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Posted 21 October 2022 - 02:50 PM

Just to give you all an example of what I'm facing, here is a screenshot of the Witch Head IC 2118.

 

This wasn't an issue until after I tuned up my Octopi tilt adapter.  

 

Yes that is exactly what I was getting - rainbow arcs, just the same. Do as above, and they will disappear.


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#35 Fegato

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Posted 16 March 2023 - 05:45 AM

I just got myself a square 50x50 UFC filter holder, as I thought this would reduce my vignetting a lot, caused by the 2" round filter. I have dark skies, so shoot mostly broadband. So I'm not too bothered that there isn't a 50x50 dual narrowband filter available, I'm happy to use separate Ha and OIII when I do go narrowband.

 

Anyway - turns out it makes no difference!  The little circle of flocking at the end of the lens group that fixes this reflection issue is causing a fair bit of vignetting itself. Oh well, back to the drawing board. I will try some progressively narrower rings to see how small I can make it (I'm getting some 3D printed). Anyone found a sweet spot any smaller than around 4-5mm, or does it have to be that small?

 

PS I finally got round to raising a ticket on this issue with Celestron, really for their info.


Edited by Fegato, 16 March 2023 - 06:05 AM.


#36 tom_halsingland

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Posted 11 May 2023 - 04:28 AM

Hi,

 

can it be reflections of the camera body? the ZWO asi-cameras reflect a lot of "rainbow" strikes, I guess. May be one shall try use a "sock" with some holes for the fan outlet over the camera body?

 

\Tom 



#37 mayhem13

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Posted 11 May 2023 - 05:37 AM

Hi,

 

can it be reflections of the camera body? the ZWO asi-cameras reflect a lot of "rainbow" strikes, I guess. May be one shall try use a "sock" with some holes for the fan outlet over the camera body?

 

\Tom 

I’ve always wondered about these glossy anodized and polished camera bodies with RASA and Hyperstar……and the heat plume coming from the fan right in the photon path…..but I suppose that can be mitigated with not capturing while the sensor is cooling.



#38 Fegato

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Posted 11 May 2023 - 07:45 AM

Hi,

 

can it be reflections of the camera body? the ZWO asi-cameras reflect a lot of "rainbow" strikes, I guess. May be one shall try use a "sock" with some holes for the fan outlet over the camera body?

 

\Tom 

I don't think so. As in the posts above, it's been fixed for us by blocking the outside few millimetres of the lens group glass. I don't think camera reflections would be fixed by this. Also, I would have thought any reflection from outside the front of the RASA would be much more diffuse?



#39 dlasserre

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Posted 09 June 2023 - 01:10 AM

I just got myself a square 50x50 UFC filter holder, as I thought this would reduce my vignetting a lot, caused by the 2" round filter. I have dark skies, so shoot mostly broadband. So I'm not too bothered that there isn't a 50x50 dual narrowband filter available, I'm happy to use separate Ha and OIII when I do go narrowband.

 

Anyway - turns out it makes no difference!  The little circle of flocking at the end of the lens group that fixes this reflection issue is causing a fair bit of vignetting itself. Oh well, back to the drawing board. I will try some progressively narrower rings to see how small I can make it (I'm getting some 3D printed). Anyone found a sweet spot any smaller than around 4-5mm, or does it have to be that small?

 

PS I finally got round to raising a ticket on this issue with Celestron, really for their info.

Hi,

 

What the answer of Celestron ?

 

Thx.



#40 Fegato

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Posted 09 June 2023 - 01:12 AM

Hi,

 

What the answer of Celestron ?

 

Thx.

No response I'm afraid. I haven't chased them.



#41 mosman1

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Posted 09 September 2023 - 04:13 PM

I also have RASA 11 v2 using with zwo large format camera, and have noticed one or two faint rainbows appear in stacked images, which are very hard to see in single subs.  I use Baader UFC so I have to remove the Celestron optical window for the UFC scope adapter to fit in correctly.

I notice that with UFC off and shining a dimmed flashlight into the RASA lens cell, multiple arc reflections of exact same shape as rainbows in the images appear.  No doubt these cause the problem.

 

I plan to try the 3D printed part since there is no good way to secure a 5mm floc ring in place without the Celestron optical window ring. Will likely get some vignetting but may be able to minimize that by using flats.



#42 sigxcpu

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Posted 02 November 2023 - 04:23 AM

Hi Robin,

 

It looks like the flocking material around the edge of the lens group does fix the issue - at least with my limited testing this evening. I decided to remove the flocking material and imaged a patch of the sky that exhibited rainbows, then re-added the flocking material and imaged the same exact patch of sky to see if the rainbows disappeared.

 

In the screenshot below, you can see on the left two faint rainbow artifacts on the single 60-second frame captured with no flocking material. Then on the right, the same exact framing and camera rotation, but this time with the flocking material. These are just single 60-second frames with an ABE in PixInsight. There are no rainbows visible!

 

attachicon.gif Rainbows.jpg

 

I actually added a narrower circle of flocking material this time (~5.5mm), and that appears to be enough. I made sure it was black on both sides by sticking two bits of flocking material back to back, just in case the white backing paper causes any side effects due to its reflectivity. Obviously time will tell whether this definitely resolves the issue, or whether any other bright stars in different parts of the field of view still cause rainbows. 

 

attachicon.gif FlockingMaterial.jpg

 

Have you had a chance to test something similar?

I didn't notice the rainbows in my images, but what I do see and it is the same in your images are the dark red rings. They happen with or without a filter.

 

Did anyone notice these and/or find a solution for them? There is a big one that touches the top and bottom edges and then concentric ones outside and inside less visible.

The train is Baader UFC, Baader tilter, Baader rings, RASA adapter, everything S70 up to M48 adapter to the ASI2600 camera. The filter holder is the first mounted thing on the camera.

 

LE: I've tried the 3D printed part, although I don't have rainbows, and it looks like it removed the red-brown rings. At least, I cannot see them anymore.


Edited by sigxcpu, 02 November 2023 - 07:59 AM.


#43 Kevin_A

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Posted 03 November 2023 - 02:37 PM

I have only seen reflections that bad in camera spacers from being shiny black inside instead of flat black. I repainted all my 21 and 16.5mm spacers and my reflections went away. Not rasa specific related.



#44 Fegato

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Posted 03 November 2023 - 03:07 PM

I have only seen reflections that bad in camera spacers from being shiny black inside instead of flat black. I repainted all my 21 and 16.5mm spacers and my reflections went away. Not rasa specific related.

Yes, that's why we all wasted so much time flocking everything we could in the image train!

 

However, this definitely comes from inside the RASA lens group. I did send a message to Celestron pointing this out, but perhaps unsurprisingly, got no response. 



#45 alexgov

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Posted 15 March 2024 - 08:14 AM

Just to give you all an example of what I'm facing, here is a screenshot of the Witch Head IC 2118.

 

This wasn't an issue until after I tuned up my Octopi tilt adapter.  

I have the same problem with RASA 11 and the camera ASI6200MC. I get exactly the same shape of a parasitic rainbow in my frames as in your photo. Did you somehow solve the problem for a full frame camera? Thanks in advance for your help.



#46 Fegato

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Posted 16 March 2024 - 04:40 AM

I have the same problem with RASA 11 and the camera ASI6200MC. I get exactly the same shape of a parasitic rainbow in my frames as in your photo. Did you somehow solve the problem for a full frame camera? Thanks in advance for your help.

Mine is full frame - ASI2400MC Pro. You need to follow the advice above - blocking the light path for 3-4mm around the lens group. This "solves" the problem - but is not great, as it blocks the light path a bit,  creating quite severe vignetting with a full frame camera (unless you are using 2" filters, which create about the same amount of vignetting)



#47 alexgov

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Posted 18 March 2024 - 07:43 AM

Mine is full frame - ASI2400MC Pro. You need to follow the advice above - blocking the light path for 3-4mm around the lens group. This "solves" the problem - but is not great, as it blocks the light path a bit,  creating quite severe vignetting with a full frame camera (unless you are using 2" filters, which create about the same amount of vignetting)

Thanks for your reply. It's strange that I also have these reflections - I didn't unscrew the RASA optical window (I don't use additional filters). If I understand correctly, I should make the aperture smaller than the optical window itself (68mm). How much do you recommend? 64mm? Is it better to make a thin ring and press it with an optical window? Thanks in advance.



#48 Fegato

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Posted 18 March 2024 - 07:49 AM

I don't think the optical window makes much difference - it's having a wide image train that allows the problem to occur. I do use filters, and have taken the glass out of my optical window and screwed it in to try and hold the flocking paper in place (but I think there's a lip which means it doesn't really hold if very well). So yes - I just cut a small ring (c 4mm) of flocking paper to fit around the outside of the lens group. It does normally just stay where it is, as the OTA is normally pointing upwards (and I never point it downwards!).



#49 alexgov

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Posted 21 March 2024 - 07:03 AM

Thank you, I will be grateful for your help. Unfortunately, my telescope is located on a remote hosting and I cannot accurately measure the required outer diameter for the ring. Strange, the RASA description indicates the thread size for the optical window - M75x0.75mm. I printed a ring from the above 3D model - there is a ring with an outer diameter of 76mm (it is not clear how it should fit into the M75 thread, although it fits in the photo) and an inner one of 62mm with a thickness of 1.5mm. You are talking about an additional reduction of the aperture by 4mm. My question - what internal diameter is ultimately best to make? 68mm is the optical window now. Then 62-68mm in this range, what is better to choose? Sorry to ask for help again. But I need to make a ring to send to a remote observatory.

I don't think the optical window makes much difference - it's having a wide image train that allows the problem to occur. I do use filters, and have taken the glass out of my optical window and screwed it in to try and hold the flocking paper in place (but I think there's a lip which means it doesn't really hold if very well). So yes - I just cut a small ring (c 4mm) of flocking paper to fit around the outside of the lens group. It does normally just stay where it is, as the OTA is normally pointing upwards (and I never point it downwards!).



#50 Fegato

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Posted 22 March 2024 - 08:12 AM

It's important to note that this ring is not connected in any way to the optical window. It sits on the lens group glass behind the optical window. I think this glass width is 76mm as per the 3D ring above. I can't check mine right now as it's attached, but I'll be taking it off in the next few days and will check it then.

 

Note - I suspect the 3D part is for use without the optical window in place. You may need to message the creator to check that.




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