Stowaway spacing adjustment #file-notice


Arun Hegde
 

Hello,

I recently purchased a Stowaway with 92TCC reducer/flattener and am in the process of doing spacing optimizations using a ZWO 2600 MC Pro camera. The nominal spacing for the Stowaway/92TCC is 64.1 mm. Attached are three images, taken at nominal -1mm, nominal -0.5mm, and nominal+0mm. It does seem like as I increase spacing, astigmatism is being reduced and suggests I need to increase spacing further. I'm posting these images to get answers to two questions:

  1. In previous, admittedly limited, spacing tests I have done with other scopes, I have not seen astigmatism, but rather coma being reduced as spacing reaches optimal. Just wanted to confirm this is expected behavior seen from a Stowaway with 92TCC.
  2. Is the 92TCC that sensitive to where 0.5mm changes make significant differences?
Thanks in advance for the replies. All there are 180s images on a well tracking Mach 1, motorized focus disregarding the outer 30% of the frame.


 

Hello Arun,

 

The three pictures that you posted show tilt in your camera. Before you can address the spacing, you need to fix the tilt. I would suggest that you do this with the nominal spacing. When all 4 corners show the same amount and shape of the stars, then the tilt is gone. For example, with the center stars properly focused, the stars in all 4 corners will either all point to the center or they will all point away from the center. But they will all have similar shape. One the tilt is gone, then you will probably find that the nominal spacing will work for your camera. I’m assuming this is not a full frame 35mm chip size because the TCC will not cover that size chip. Only the field flattener will work for a full frame 35mm camera.

 

Roland Christen

Astro-Physics Inc.

 

From: main@ap-ug.groups.io <main@ap-ug.groups.io> On Behalf Of Arun Hegde
Sent: Tuesday, October 26, 2021 12:50 PM
To: main@ap-ug.groups.io
Subject: [ap-ug] Stowaway spacing adjustment #file-notice

 

Hello,

I recently purchased a Stowaway with 92TCC reducer/flattener and am in the process of doing spacing optimizations using a ZWO 2600 MC Pro camera. The nominal spacing for the Stowaway/92TCC is 64.1 mm. Attached are three images, taken at nominal -1mm, nominal -0.5mm, and nominal+0mm. It does seem like as I increase spacing, astigmatism is being reduced and suggests I need to increase spacing further. I'm posting these images to get answers to two questions:

  1. In previous, admittedly limited, spacing tests I have done with other scopes, I have not seen astigmatism, but rather coma being reduced as spacing reaches optimal. Just wanted to confirm this is expected behavior seen from a Stowaway with 92TCC.
  2. Is the 92TCC that sensitive to where 0.5mm changes make significant differences?

Thanks in advance for the replies. All there are 180s images on a well tracking Mach 1, motorized focus disregarding the outer 30% of the frame.


 

Aberrations in an optical system can be traced to the various elements by how thet appear over the frame. If the main lens was out of collimation, then all stars over the entire chip would be oval shaped in exactly the same direction. This is not the case in your images so you can rule out the main optics. It’s not possible for the Feathertouch focuser to be tilted. It is possible for the camera adapter dovetail attachment to be tilted – you can check that visually. Make sure that it seats flat against the focuser end when you tighten the three thumb screws. The last  possibility is that the TCC reducer is internally miscollimated. If you send it back, I can check it out when I return to the factory on the Monday after next. No need to return the Stowaway itself.

By the way, you can look at stars with the scope visually and see that it works correctly – it’s the easiest test in the world.

 

Roland Christen

Astro-Physics Inc.

 

From: main@ap-ug.groups.io <main@ap-ug.groups.io
Sent: Tuesday, October 26, 2021 11:14 PM
To: main@ap-ug.groups.io
Subject: Re: [ap-ug] Stowaway spacing adjustment #file-notice

 

Hello Arun,

 

The three pictures that you posted show tilt in your camera. Before you can address the spacing, you need to fix the tilt. I would suggest that you do this with the nominal spacing. When all 4 corners show the same amount and shape of the stars, then the tilt is gone. For example, with the center stars properly focused, the stars in all 4 corners will either all point to the center or they will all point away from the center. But they will all have similar shape. One the tilt is gone, then you will probably find that the nominal spacing will work for your camera. I’m assuming this is not a full frame 35mm chip size because the TCC will not cover that size chip. Only the field flattener will work for a full frame 35mm camera.

 

Roland Christen

Astro-Physics Inc.

 

From: main@ap-ug.groups.io <main@ap-ug.groups.io> On Behalf Of Arun Hegde
Sent: Tuesday, October 26, 2021 12:50 PM
To: main@ap-ug.groups.io
Subject: [ap-ug] Stowaway spacing adjustment #file-notice

 

Hello,

I recently purchased a Stowaway with 92TCC reducer/flattener and am in the process of doing spacing optimizations using a ZWO 2600 MC Pro camera. The nominal spacing for the Stowaway/92TCC is 64.1 mm. Attached are three images, taken at nominal -1mm, nominal -0.5mm, and nominal+0mm. It does seem like as I increase spacing, astigmatism is being reduced and suggests I need to increase spacing further. I'm posting these images to get answers to two questions:

  1. In previous, admittedly limited, spacing tests I have done with other scopes, I have not seen astigmatism, but rather coma being reduced as spacing reaches optimal. Just wanted to confirm this is expected behavior seen from a Stowaway with 92TCC.
  2. Is the 92TCC that sensitive to where 0.5mm changes make significant differences?

Thanks in advance for the replies. All there are 180s images on a well tracking Mach 1, motorized focus disregarding the outer 30% of the frame.


 

I did find one 92 Stowaway customer image of the same field taken with a 35mm full frame camera, so it appears that it is possible with the 92 Stowaway and 0.8 TCC: https://www.astrobin.com/x9ia06/0/

 

Roland Christen

 

From: main@ap-ug.groups.io <main@ap-ug.groups.io> On Behalf Of Marj Christen
Sent: Tuesday, October 26, 2021 11:14 PM
To: main@ap-ug.groups.io
Subject: Re: [ap-ug] Stowaway spacing adjustment #file-notice

 

Hello Arun,

 

The three pictures that you posted show tilt in your camera. Before you can address the spacing, you need to fix the tilt. I would suggest that you do this with the nominal spacing. When all 4 corners show the same amount and shape of the stars, then the tilt is gone. For example, with the center stars properly focused, the stars in all 4 corners will either all point to the center or they will all point away from the center. But they will all have similar shape. One the tilt is gone, then you will probably find that the nominal spacing will work for your camera. I’m assuming this is not a full frame 35mm chip size because the TCC will not cover that size chip. Only the field flattener will work for a full frame 35mm camera.

 

Roland Christen

Astro-Physics Inc.

 

From: main@ap-ug.groups.io <main@ap-ug.groups.io> On Behalf Of Arun Hegde
Sent: Tuesday, October 26, 2021 12:50 PM
To: main@ap-ug.groups.io
Subject: [ap-ug] Stowaway spacing adjustment #file-notice

 

Hello,

I recently purchased a Stowaway with 92TCC reducer/flattener and am in the process of doing spacing optimizations using a ZWO 2600 MC Pro camera. The nominal spacing for the Stowaway/92TCC is 64.1 mm. Attached are three images, taken at nominal -1mm, nominal -0.5mm, and nominal+0mm. It does seem like as I increase spacing, astigmatism is being reduced and suggests I need to increase spacing further. I'm posting these images to get answers to two questions:

  1. In previous, admittedly limited, spacing tests I have done with other scopes, I have not seen astigmatism, but rather coma being reduced as spacing reaches optimal. Just wanted to confirm this is expected behavior seen from a Stowaway with 92TCC.
  2. Is the 92TCC that sensitive to where 0.5mm changes make significant differences?

Thanks in advance for the replies. All there are 180s images on a well tracking Mach 1, motorized focus disregarding the outer 30% of the frame.


Bill Long
 

The ZWO cameras are really poorly QC'd and most have tilted sensors.


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Marj Christen <marj@...>
Sent: Tuesday, October 26, 2021 9:13 PM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway spacing adjustment #file-notice
 

Hello Arun,

 

The three pictures that you posted show tilt in your camera. Before you can address the spacing, you need to fix the tilt. I would suggest that you do this with the nominal spacing. When all 4 corners show the same amount and shape of the stars, then the tilt is gone. For example, with the center stars properly focused, the stars in all 4 corners will either all point to the center or they will all point away from the center. But they will all have similar shape. One the tilt is gone, then you will probably find that the nominal spacing will work for your camera. I’m assuming this is not a full frame 35mm chip size because the TCC will not cover that size chip. Only the field flattener will work for a full frame 35mm camera.

 

Roland Christen

Astro-Physics Inc.

 

From: main@ap-ug.groups.io <main@ap-ug.groups.io> On Behalf Of Arun Hegde
Sent: Tuesday, October 26, 2021 12:50 PM
To: main@ap-ug.groups.io
Subject: [ap-ug] Stowaway spacing adjustment #file-notice

 

Hello,

I recently purchased a Stowaway with 92TCC reducer/flattener and am in the process of doing spacing optimizations using a ZWO 2600 MC Pro camera. The nominal spacing for the Stowaway/92TCC is 64.1 mm. Attached are three images, taken at nominal -1mm, nominal -0.5mm, and nominal+0mm. It does seem like as I increase spacing, astigmatism is being reduced and suggests I need to increase spacing further. I'm posting these images to get answers to two questions:

  1. In previous, admittedly limited, spacing tests I have done with other scopes, I have not seen astigmatism, but rather coma being reduced as spacing reaches optimal. Just wanted to confirm this is expected behavior seen from a Stowaway with 92TCC.
  2. Is the 92TCC that sensitive to where 0.5mm changes make significant differences?

Thanks in advance for the replies. All there are 180s images on a well tracking Mach 1, motorized focus disregarding the outer 30% of the frame.


Arun Hegde
 

Thank you Roland.

I certainly agree that there is some tilt in my ZWO camera... I am yet to see a ZWO camera that doesn't have some degree of tilt. That is why I focused on the middle of the frame. However, the degree of tilt in that 2600 (which is APS-C) is not so significant that it has shown significant distortions in the center of the frame when I have used it with my 80mm refractor. 

I fully agree that the main optics are sound - I checked with a cheshire and they are perfectly collimated. The focuser is rock solid and a laser collimator shows no tilt in it. I'll send in the 92TCC just to remove that variable. Thanks again.


Bill Long
 

Was the 80mm refractor F5.3 and using a compressed field?


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Arun Hegde <arun.k.hegde@...>
Sent: Wednesday, October 27, 2021 3:27 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway spacing adjustment #file-notice
 
Thank you Roland.

I certainly agree that there is some tilt in my ZWO camera... I am yet to see a ZWO camera that doesn't have some degree of tilt. That is why I focused on the middle of the frame. However, the degree of tilt in that 2600 (which is APS-C) is not so significant that it has shown significant distortions in the center of the frame when I have used it with my 80mm refractor. 

I fully agree that the main optics are sound - I checked with a cheshire and they are perfectly collimated. The focuser is rock solid and a laser collimator shows no tilt in it. I'll send in the 92TCC just to remove that variable. Thanks again.


Bill Long
 

Also center of the field won't show tilt issues because the axis doesn't really allow for that to be possible. 


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Arun Hegde <arun.k.hegde@...>
Sent: Wednesday, October 27, 2021 3:27 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway spacing adjustment #file-notice
 
Thank you Roland.

I certainly agree that there is some tilt in my ZWO camera... I am yet to see a ZWO camera that doesn't have some degree of tilt. That is why I focused on the middle of the frame. However, the degree of tilt in that 2600 (which is APS-C) is not so significant that it has shown significant distortions in the center of the frame when I have used it with my 80mm refractor. 

I fully agree that the main optics are sound - I checked with a cheshire and they are perfectly collimated. The focuser is rock solid and a laser collimator shows no tilt in it. I'll send in the 92TCC just to remove that variable. Thanks again.


Bill Long
 

Tilt causes a change in focus across the frame, and in systems with a corrector it also changes the star patterns due to the corrector influence on the field differing. 

So to say "hey my 80mm scope shows XYZ" isn't as relevant as one would assume naturally.

You're comparing the outcomes of two largely different scenarios.


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Bill Long <bill@...>
Sent: Wednesday, October 27, 2021 3:54 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway spacing adjustment #file-notice
 
Also center of the field won't show tilt issues because the axis doesn't really allow for that to be possible. 


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Arun Hegde <arun.k.hegde@...>
Sent: Wednesday, October 27, 2021 3:27 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway spacing adjustment #file-notice
 
Thank you Roland.

I certainly agree that there is some tilt in my ZWO camera... I am yet to see a ZWO camera that doesn't have some degree of tilt. That is why I focused on the middle of the frame. However, the degree of tilt in that 2600 (which is APS-C) is not so significant that it has shown significant distortions in the center of the frame when I have used it with my 80mm refractor. 

I fully agree that the main optics are sound - I checked with a cheshire and they are perfectly collimated. The focuser is rock solid and a laser collimator shows no tilt in it. I'll send in the 92TCC just to remove that variable. Thanks again.


Arun Hegde
 

Hi Roland,

To answer your other question, yes, I will address the tilt in my camera at nominal spacing once I get the 92TCC checked and back. I also have a 92FF on order which can help me check my camera tilt independently of the 92TCC. 

Bill - the 80mm is f/4.8 with reducer.

Arun


M Hambrick
 

Hi Arun

If tilt is your problem you should also make sure that the 92TCC is fitting properly into the Doveloc adapter. Look for dimples from the lock screws in the bottom of the groove of the 92TCC. If you see dimples like those shown in the attached photo, then there is a good chance that the 92TCC and camera are not being positioned correctly when you attach it. To seat properly, the tapered tip of the lock screws should be making contact with the angled shoulder of the groove in the 92TCC. You can see how this should work in the drawing.

I believe that the root cause of this issue is that the lock screw holes in the Doveloc adapter are drilled in the wrong location (too close to the back face by about 0.030"). However, you can correct this issue by filing the sharp tip off of the lock screws so that only the tapered part makes contact with the angled shoulder of the 92TCC.

Mike

 


Arun Hegde
 
Edited

Thanks for that tip, Mike. Earlier this morning I checked the groove on the 92TCC. I do not see any dimples there. I do see slight marring on the lip/shoulder where the screws made contact with the 92TCC. I believe this would be normal based on your diagram. Thanks again.

Also, Mike, your diagram was also very helpful in me understanding the other suggestion that Roland had, which was to assure that the adapter sat flush against the focuser once the screws were tightened. So thanks for sharing that.


ROBERT WYNNE
 

Yes these screws were designed to jam the 92CC towards the flange to assure a closely coupled flat fit to the glange and certainly not to affix the doveloc to the barrel incorrectly postioned some few thousand'ths of an inch away from the flange. -Best, Robert

On 10/27/2021 5:56 AM M Hambrick <mhambrick563@...> wrote:


Hi Arun

If tilt is your problem you should also make sure that the 92TCC is fitting properly into the Doveloc adapter. Look for dimples from the lock screws in the bottom of the groove of the 92TCC. If you see dimples like those shown in the attached photo, then there is a good chance that the 92TCC and camera are not being positioned correctly when you attach it. To seat properly, the tapered tip of the lock screws should be making contact with the angled shoulder of the groove in the 92TCC. You can see how this should work in the drawing.

I believe that the root cause of this issue is that the lock screw holes in the Doveloc adapter are drilled in the wrong location (too close to the back face by about 0.030"). However, you can correct this issue by filing the sharp tip off of the lock screws so that only the tapered part makes contact with the angled shoulder of the 92TCC.

Mike

 


ROBERT WYNNE
 

That should have been flange not glange. -Best, Robert

On 10/27/2021 7:01 PM ROBERT WYNNE <robert-wynne@...> wrote:


Yes these screws were designed to jam the 92CC towards the flange to assure a closely coupled flat fit to the glange and certainly not to affix the doveloc to the barrel incorrectly postioned some few thousand'ths of an inch away from the flange. -Best, Robert
On 10/27/2021 5:56 AM M Hambrick <mhambrick563@...> wrote:


Hi Arun

If tilt is your problem you should also make sure that the 92TCC is fitting properly into the Doveloc adapter. Look for dimples from the lock screws in the bottom of the groove of the 92TCC. If you see dimples like those shown in the attached photo, then there is a good chance that the 92TCC and camera are not being positioned correctly when you attach it. To seat properly, the tapered tip of the lock screws should be making contact with the angled shoulder of the groove in the 92TCC. You can see how this should work in the drawing.

I believe that the root cause of this issue is that the lock screw holes in the Doveloc adapter are drilled in the wrong location (too close to the back face by about 0.030"). However, you can correct this issue by filing the sharp tip off of the lock screws so that only the tapered part makes contact with the angled shoulder of the 92TCC.

Mike