Topics

Optimizing Quad TCC Backfocus Spacing


M Hambrick
 

I recall a discussion on this a while back, but I can not find it. A-P sells sets of 1 mm spacer rings for tweaking the backfocus spacing of the Quad TCC. Is there a particular methodology for determining the optimum backfocus distance ? I took some test images the other night with zero, one, and two spacers. Looking at the corners of these images I can see differences visually, but if I compare the statistics (FWHM, Flatness, & Max Pixel) for a reference star in each corner, they do not really agree with what I can see in the images.


Roland Christen
 

What scope are you using? Optimum spacing also depends on the size of the chip.

Rolando



-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Mon, Dec 28, 2020 8:18 am
Subject: [ap-ug] Optimizing Quad TCC Backfocus Spacing

I recall a discussion on this a while back, but I can not find it. A-P sells sets of 1 mm spacer rings for tweaking the backfocus spacing of the Quad TCC. Is there a particular methodology for determining the optimum backfocus distance ? I took some test images the other night with zero, one, and two spacers. Looking at the corners of these images I can see differences visually, but if I compare the statistics (FWHM, Flatness, & Max Pixel) for a reference star in each corner, they do not really agree with what I can see in the images.


James Stone
 

Not to hijack this thread, but I actually had a similar question for use of a quad TCC as well as a 67PF582 with a 155 EDF upgraded to a 3.5” focuser with a 16803 chip.

 

From: <main@ap-ug.groups.io> on behalf of "Roland Christen via groups.io" <chris1011@...>
Reply-To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Date: Monday, December 28, 2020 at 11:53 AM
To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing

 

What scope are you using? Optimum spacing also depends on the size of the chip.

 

Rolando

 

 

 

-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Mon, Dec 28, 2020 8:18 am
Subject: [ap-ug] Optimizing Quad TCC Backfocus Spacing

I recall a discussion on this a while back, but I can not find it. A-P sells sets of 1 mm spacer rings for tweaking the backfocus spacing of the Quad TCC. Is there a particular methodology for determining the optimum backfocus distance ? I took some test images the other night with zero, one, and two spacers. Looking at the corners of these images I can see differences visually, but if I compare the statistics (FWHM, Flatness, & Max Pixel) for a reference star in each corner, they do not really agree with what I can see in the images.


Roland Christen
 

Up to now we have not made a specific spacer for this telescope. I have a theoretical distance based on the optical design. I just received a new 35mm format camera to replace one that failed, and if the weather holds out tonight I will be able to verify the correct spacing for the 155EDF.

Roland Christen
Astro-Physics Inc.



-----Original Message-----
From: James Stone <jrs7r@...>
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Mon, Dec 28, 2020 10:58 am
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing

Not to hijack this thread, but I actually had a similar question for use of a quad TCC as well as a 67PF582 with a 155 EDF upgraded to a 3.5” focuser with a 16803 chip.
 
From: <main@ap-ug.groups.io> on behalf of "Roland Christen via groups.io" <chris1011@...>
Reply-To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Date: Monday, December 28, 2020 at 11:53 AM
To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing
 
What scope are you using? Optimum spacing also depends on the size of the chip.
 
Rolando
 
 
 
-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Mon, Dec 28, 2020 8:18 am
Subject: [ap-ug] Optimizing Quad TCC Backfocus Spacing
I recall a discussion on this a while back, but I can not find it. A-P sells sets of 1 mm spacer rings for tweaking the backfocus spacing of the Quad TCC. Is there a particular methodology for determining the optimum backfocus distance ? I took some test images the other night with zero, one, and two spacers. Looking at the corners of these images I can see differences visually, but if I compare the statistics (FWHM, Flatness, & Max Pixel) for a reference star in each corner, they do not really agree with what I can see in the images.


James Stone
 

That’s great, thank you!

 

From: <main@ap-ug.groups.io> on behalf of "Roland Christen via groups.io" <chris1011@...>
Reply-To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Date: Monday, December 28, 2020 at 12:19 PM
To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing

 

Up to now we have not made a specific spacer for this telescope. I have a theoretical distance based on the optical design. I just received a new 35mm format camera to replace one that failed, and if the weather holds out tonight I will be able to verify the correct spacing for the 155EDF.

 

Roland Christen

Astro-Physics Inc.

 

 

 

-----Original Message-----
From: James Stone <jrs7r@...>
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Mon, Dec 28, 2020 10:58 am
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing

Not to hijack this thread, but I actually had a similar question for use of a quad TCC as well as a 67PF582 with a 155 EDF upgraded to a 3.5” focuser with a 16803 chip.

 

From: <main@ap-ug.groups.io> on behalf of "Roland Christen via groups.io" <chris1011@...>
Reply-To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Date: Monday, December 28, 2020 at 11:53 AM
To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing

 

What scope are you using? Optimum spacing also depends on the size of the chip.

 

Rolando

 

 

 

-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Mon, Dec 28, 2020 8:18 am
Subject: [ap-ug] Optimizing Quad TCC Backfocus Spacing

I recall a discussion on this a while back, but I can not find it. A-P sells sets of 1 mm spacer rings for tweaking the backfocus spacing of the Quad TCC. Is there a particular methodology for determining the optimum backfocus distance ? I took some test images the other night with zero, one, and two spacers. Looking at the corners of these images I can see differences visually, but if I compare the statistics (FWHM, Flatness, & Max Pixel) for a reference star in each corner, they do not really agree with what I can see in the images.


M Hambrick
 

Hi Roland

The scope is the 180 EDT with Quad TCC that you recently sent me the modified focuser end cap for. The camera is a SBIG STXL16200 (4500 X 3600 pixels @ 6 microns). The adapter that I ordered from Precise Parts was specified assuming that there would be one of the 1 mm spacer rings. I think you should have a drawing of this setup in the emails that we exchanged previously.

To James' question, when I was trying to figure out what backfocus distance to use I plotted the known values from the A-P web site and extrapolated. When Roland gets another data point for the 155 EDF it will be interesting to see how well it fits the curve.



Tony Flores
 

Would these back focus specs also apply to the AP140SDF?


Roland Christen
 

The theoretical distance from the QTCC flange is calculated at 86.5mm. If this is confirmed by my testing, then it will not be possible to add any spacer on the back of the QTCC to bring the distance down to 80.8mm for the standard 35mm Canon back spacing. This spacer would have to be built-in to the Canon camera adapter. For all CCD cameras this is not an issue since a custom adapter will be needed anyway.

Roland Christen
Astro-Physics Inc.



-----Original Message-----
From: James Stone <jrs7r@...>
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Mon, Dec 28, 2020 11:22 am
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing

That’s great, thank you!
 
From: <main@ap-ug.groups.io> on behalf of "Roland Christen via groups.io" <chris1011@...>
Reply-To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Date: Monday, December 28, 2020 at 12:19 PM
To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing
 
Up to now we have not made a specific spacer for this telescope. I have a theoretical distance based on the optical design. I just received a new 35mm format camera to replace one that failed, and if the weather holds out tonight I will be able to verify the correct spacing for the 155EDF.
 
Roland Christen
Astro-Physics Inc.
 
 
 
-----Original Message-----
From: James Stone <jrs7r@...>
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Mon, Dec 28, 2020 10:58 am
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing
Not to hijack this thread, but I actually had a similar question for use of a quad TCC as well as a 67PF582 with a 155 EDF upgraded to a 3.5” focuser with a 16803 chip.
 
From: <main@ap-ug.groups.io> on behalf of "Roland Christen via groups.io" <chris1011@...>
Reply-To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Date: Monday, December 28, 2020 at 11:53 AM
To: "main@ap-ug.groups.io" <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing
 
What scope are you using? Optimum spacing also depends on the size of the chip.
 
Rolando
 
 
 
-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Mon, Dec 28, 2020 8:18 am
Subject: [ap-ug] Optimizing Quad TCC Backfocus Spacing
I recall a discussion on this a while back, but I can not find it. A-P sells sets of 1 mm spacer rings for tweaking the backfocus spacing of the Quad TCC. Is there a particular methodology for determining the optimum backfocus distance ? I took some test images the other night with zero, one, and two spacers. Looking at the corners of these images I can see differences visually, but if I compare the statistics (FWHM, Flatness, & Max Pixel) for a reference star in each corner, they do not really agree with what I can see in the images.


Roland Christen
 

The 155EDF is a completely different optical design with inherently less field curvature than the other scopes that we make spacers for. Therefore the back distance is considerably less than the TEC scopes.

I will do an analysis of the 180 EDT and report back. I am guessing that the back distance will be closer to 80mm for that scope.

Roland



-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Mon, Dec 28, 2020 12:07 pm
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing

Hi Roland

The scope is the 180 EDT with Quad TCC that you recently sent me the modified focuser end cap for. The camera is a SBIG STXL16200 (4500 X 3600 pixels @ 6 microns). The adapter that I ordered from Precise Parts was specified assuming that there would be one of the 1 mm spacer rings. I think you should have a drawing of this setup in the emails that we exchanged previously.

To James' question, when I was trying to figure out what backfocus distance to use I plotted the known values from the A-P web site and extrapolated. When Roland gets another data point for the 155 EDF it will be interesting to see how well it fits the curve.



M Hambrick
 

Oh wow ! I hope it is longer than 80 mm for the 180 EDT. My custom Quad TCC to Camera adapter from Precise Parts was just delivered, and I specified the length based on the estimate of 95.4 mm in the graph above that I arrived at by extrapolating the graph of the backfocus distances for the 130 GTX and TEC scopes.


Roland Christen
 

I just checked the original calculations for the 180EDT. The distance is 93.5mm+-1mm for a 35mm format chip.

Roland



-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Mon, Dec 28, 2020 2:59 pm
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing

Oh wow ! I hope it is longer than 80 mm for the 180 EDT. My custom Quad TCC to Camera adapter from Precise Parts was just delivered, and I specified the length based on the estimate of 95.4 mm in the graph above that I arrived at by extrapolating the graph of the backfocus distances for the 130 GTX and TEC scopes.


Tony Flores
 

What are the back focus specs for the AP140SDF with the 4” focuser?


Terri Zittritsch
 

Roland, I just ordered spacers for my TEC 140 and Stowaway to use a full frame camera (spacers arrive in a few weeks).    I use the Quad TCC and 92TCC on these two scopes and have used the spec spacing as defined in your literature for each with my ASI1600MM camera, and it works well.   I assumed that the new camera would be no different for a full frame mono camera.  I accounted for the filter as well.    I do use the 18.3mm spacer on the back of the QuadTCC so if I have an issue could have another spacer made different than 18.3mm to account for issues.    But on the Stowaway and the 92TCC, I can only make the spacing longer without tossing away the spacer.     

I didn't realize there is a chip size dependence in the back-focus spacing.     

Do you have a feeling on how this changes with chip size and what chip size is assumed for the back spacing specified?

Terri


Dale Ghent
 

Chip size does not change the spacing that is required.  It does change how accurate that spacing has to be, and how flat the field produced by the flattener has to be. The larger the chip, the more exact the spacing and more performant the flattener must be. 

On Dec 29, 2020, at 10:08 AM, Terri Zittritsch <theresamarie11@...> wrote:



Roland, I just ordered spacers for my TEC 140 and Stowaway to use a full frame camera (spacers arrive in a few weeks).    I use the Quad TCC and 92TCC on these two scopes and have used the spec spacing as defined in your literature for each with my ASI1600MM camera, and it works well.   I assumed that the new camera would be no different for a full frame mono camera.  I accounted for the filter as well.    I do use the 18.3mm spacer on the back of the QuadTCC so if I have an issue could have another spacer made different than 18.3mm to account for issues.    But on the Stowaway and the 92TCC, I can only make the spacing longer without tossing away the spacer.     

I didn't realize there is a chip size dependence in the back-focus spacing.     

Do you have a feeling on how this changes with chip size and what chip size is assumed for the back spacing specified?

Terri


Bill Long
 

Yeah thats going to be a big NO for me. Not good to spread false statements. 


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Dale Ghent <daleg@...>
Sent: Tuesday, December 29, 2020 7:19 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing
 
Chip size does not change the spacing that is required.  It does change how accurate that spacing has to be, and how flat the field produced by the flattener has to be. The larger the chip, the more exact the spacing and more performant the flattener must be. 

On Dec 29, 2020, at 10:08 AM, Terri Zittritsch <theresamarie11@...> wrote:



Roland, I just ordered spacers for my TEC 140 and Stowaway to use a full frame camera (spacers arrive in a few weeks).    I use the Quad TCC and 92TCC on these two scopes and have used the spec spacing as defined in your literature for each with my ASI1600MM camera, and it works well.   I assumed that the new camera would be no different for a full frame mono camera.  I accounted for the filter as well.    I do use the 18.3mm spacer on the back of the QuadTCC so if I have an issue could have another spacer made different than 18.3mm to account for issues.    But on the Stowaway and the 92TCC, I can only make the spacing longer without tossing away the spacer.     

I didn't realize there is a chip size dependence in the back-focus spacing.     

Do you have a feeling on how this changes with chip size and what chip size is assumed for the back spacing specified?

Terri


Dale Ghent
 

Care to expand upon this mental tic?

On Dec 29, 2020, at 10:22 AM, Bill Long <bill@...> wrote:


Yeah thats going to be a big NO for me. Not good to spread false statements. 


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Dale Ghent <daleg@...>
Sent: Tuesday, December 29, 2020 7:19 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing
 
Chip size does not change the spacing that is required.  It does change how accurate that spacing has to be, and how flat the field produced by the flattener has to be. The larger the chip, the more exact the spacing and more performant the flattener must be. 

On Dec 29, 2020, at 10:08 AM, Terri Zittritsch <theresamarie11@...> wrote:



Roland, I just ordered spacers for my TEC 140 and Stowaway to use a full frame camera (spacers arrive in a few weeks).    I use the Quad TCC and 92TCC on these two scopes and have used the spec spacing as defined in your literature for each with my ASI1600MM camera, and it works well.   I assumed that the new camera would be no different for a full frame mono camera.  I accounted for the filter as well.    I do use the 18.3mm spacer on the back of the QuadTCC so if I have an issue could have another spacer made different than 18.3mm to account for issues.    But on the Stowaway and the 92TCC, I can only make the spacing longer without tossing away the spacer.     

I didn't realize there is a chip size dependence in the back-focus spacing.     

Do you have a feeling on how this changes with chip size and what chip size is assumed for the back spacing specified?

Terri


James Stone
 

Bill, can you elaborate?


On Dec 29, 2020, at 10:22 AM, Bill Long <bill@...> wrote:


Yeah thats going to be a big NO for me. Not good to spread false statements. 


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Dale Ghent <daleg@...>
Sent: Tuesday, December 29, 2020 7:19 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing
 
Chip size does not change the spacing that is required.  It does change how accurate that spacing has to be, and how flat the field produced by the flattener has to be. The larger the chip, the more exact the spacing and more performant the flattener must be. 

On Dec 29, 2020, at 10:08 AM, Terri Zittritsch <theresamarie11@...> wrote:



Roland, I just ordered spacers for my TEC 140 and Stowaway to use a full frame camera (spacers arrive in a few weeks).    I use the Quad TCC and 92TCC on these two scopes and have used the spec spacing as defined in your literature for each with my ASI1600MM camera, and it works well.   I assumed that the new camera would be no different for a full frame mono camera.  I accounted for the filter as well.    I do use the 18.3mm spacer on the back of the QuadTCC so if I have an issue could have another spacer made different than 18.3mm to account for issues.    But on the Stowaway and the 92TCC, I can only make the spacing longer without tossing away the spacer.     

I didn't realize there is a chip size dependence in the back-focus spacing.     

Do you have a feeling on how this changes with chip size and what chip size is assumed for the back spacing specified?

Terri


Malik AMZIANE
 

Hello Mr Hambrick,
 
Can you send us a picture to see how the field curvature behaves?
Personally I use CCDInspector and ASTAP in addition, to get an idea of ​​the curvature and the tilt when there is any.
To know if we are too far or too close I have this image which represents the shape of the stars depending on whether the curvature is under corrected or over corrected.

Malik



Roland Christen
 

I will update the specs for a number of scopes in an upcoming post, so please wait a bit.

Rolando



-----Original Message-----
From: Tony Flores via groups.io <tflores@...>
To: main@ap-ug.groups.io
Sent: Tue, Dec 29, 2020 12:48 am
Subject: Re: [ap-ug] Optimizing Quad TCC Backfocus Spacing

What are the back focus specs for the AP140SDF with the 4” focuser?


Terri Zittritsch
 

On Tue, Dec 29, 2020 at 12:39 PM, Roland Christen wrote:
I will update the specs for a number of scopes in an upcoming post, so please wait a bit.
 
Rolando
 
Thanks Roland.


Terri