Topics

Stowaway with full frame sensor, 92TCC and triangular stars


Terri Zittritsch
 

Hi Roland, 
I'm hoping this is an easy question for you.     I've recently purchased a full frame mono camera and filter wheel and tried it out for the first time last night on the Stowaway with 92TCC installed.     What I expected is to find that my tilt needed to be adjusted in some way and would find elongated stars in the corners.
Instead,  what I've found  is triangular stars in all of the corners.      Now it is cold here, as February in Vermont usually is.    Last night I started imaging at 10F, and ended around 4F.    Not the subject here, but the Mach2 seems to have no issues whatsoever at low temperature.  I've used the Mach2 down to -4F without issue.    I searched for triangular stars and mostly what I find is pinched optics on mirrors/newts.      

Thoughts on the triangular stars in this case?    

best,
Terri


Roland Christen
 

If you had pinched optics then all your stars would be triangular. The 92TCC is not designed to cover a full frame 35mm chip. Part of the outer field will have stars that are vignetted and will have portion of their light cut off. The field flattener will cover a full frame, a telecompressor is a device that takes this size field and shrinks it to a smaller diameter, thus making the optic faster photographically but not necessarily making the field size bigger. Field size is limited by the size of the optics, the diameter of the barrel, and the fact that shrinking the focal ratio causes the light bundle to converge to a smaller diameter.

Roland christen



-----Original Message-----
From: Terri Zittritsch <theresamarie11@...>
To: main@ap-ug.groups.io
Sent: Tue, Feb 9, 2021 8:35 am
Subject: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars

Hi Roland, 
I'm hoping this is an easy question for you.     I've recently purchased a full frame mono camera and filter wheel and tried it out for the first time last night on the Stowaway with 92TCC installed.     What I expected is to find that my tilt needed to be adjusted in some way and would find elongated stars in the corners.
Instead,  what I've found  is triangular stars in all of the corners.      Now it is cold here, as February in Vermont usually is.    Last night I started imaging at 10F, and ended around 4F.    Not the subject here, but the Mach2 seems to have no issues whatsoever at low temperature.  I've used the Mach2 down to -4F without issue.    I searched for triangular stars and mostly what I find is pinched optics on mirrors/newts.      

Thoughts on the triangular stars in this case?    

best,
Terri


Terri Zittritsch
 
Edited

Roland, thank you for the reply.   I guess I was hopeful because I loaned a friend my 92TCC to use at the Eldorado star party this past fall with his brand spankin' new Stowaway, and he says that the reducer worked better than the flattener at the edges of the frame with his full frame EOS Ra.   That's why I wondered whether there is a temperature effect going on.    Maybe there is some added interaction with the 2" filters where the Ra only has filters/lenses at the die plane.


Terri


Bill Long
 

Perhaps he mixed up which he was using? Or maybe he had focus off a bit which have the appearance of better edge performance when in reality it would have been worse in proper focus?

A full frame chip is 43mm diagonal. The corrected field of the reducer is 40mm. You will have performance issues at the edge. That's why the reducer clearly states it's better with an APS-C sized field on their website.


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Terri Zittritsch <theresamarie11@...>
Sent: Wednesday, February 10, 2021 6:13 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars
 

[Edited Message Follows]

Roland, thank you for the reply.   I guess I was hopeful because I loaned a friend my 92TCC to use at the Eldorado star party this past fall with his brand spankin' new Stowaway, and he says that the reducer worked better than the flattener at the edges of the frame with his full frame EOS Ra.   That's why I wondered whether there is a temperature effect going on.    Maybe there is some added interaction with the 2" filters where the Ra only has filters/lenses at the die plane.


Terri


Terri Zittritsch
 

Bill, I did read the spec and it doesn't say as you noted, that it's clearly better for APS-C, what it states is that it will provide pinpoint stars to the corners of an APS-C sized sensor and that the corrected area is a 40mm circle.    40m is a little smaller than needed for a full frame (which is 43mm).    Because 40mm would be great, and kind of what I expected based on the specification with some uncorrected area in the far corners (1.5mm in the far corners).    I expected falloff of correction to occur outside of 40mm.   It seems worse than that and trying to understand why.
 
I can't count out that there is some tilt in the system but it's hard to discern with the triangular stars.     Given I'm not an optics engineer, I thought maybe there might be some further complication with the filters in the light path.   

Terri     


Bill Long
 

Pinpoint stars to the edge of a APS-C chip and a 40mm imaging circle is the same as saying it is better for a APS-C chip than it would be for a 36x24 full frame camera. 

Here is the FOV of the Stowaway and its reducer with an APSC Chip (yellow) and a Full Frame Chip (red). Note that the difference is not minor. 

Do you have a sample sub you can share from the Full Frame camera and the Stowaway with its reducer? I would imagine you start to see the field performance drop off roughly at the midpoint between these two FOVs. 




From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Terri Zittritsch <theresamarie11@...>
Sent: Wednesday, February 10, 2021 10:52 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars
 
Bill, I did read the spec and it doesn't say as you noted, that it's clearly better for APS-C, what it states is that it will provide pinpoint stars to the corners of an APS-C sized sensor and that the corrected area is a 40mm circle.    40m is a little smaller than needed for a full frame (which is 43mm).    Because 40mm would be great, and kind of what I expected based on the specification with some uncorrected area in the far corners (1.5mm in the far corners).    I expected falloff of correction to occur outside of 40mm.   It seems worse than that and trying to understand why.
 
I can't count out that there is some tilt in the system but it's hard to discern with the triangular stars.     Given I'm not an optics engineer, I thought maybe there might be some further complication with the filters in the light path.   

Terri     


Bill Long
 

Ruling out tilt is fairly important. Although you already know you are exceeding the corrected image circle, which can make that harder to diagnose. I did test the Stowaway and a 16200 chip (which is about 36mm diagonal) with its reducer, and noted that some spacing tweaks were needed to the original 64.1mm spacing AP released. I am assuming (and happy to be corrected on) that this spacing was derived using APS-C as the model size sensor. Roland of course, would know for sure! :) 


Terri Zittritsch
 
Edited


Hi Bill, I don't want to argue with you on what's inferred versus what it actually says.  The fact that it says APS-C works well doesn't really imply that the specification of  a 40mm corrected circle is somehow not to be counted on.  A 40mm corrected image circle only leaves 1.5mm on the corners, so almost full frame.   Depending on what APS-C system you have,  those require a significantly smaller image circle of 27mm or so (Canon).    

And just to be clear, I'm trying to understand what's going on, versus complaining (no need to defend anyone's honor).  In any case, getting a frame from one of my friends Eldorado star party images to compare star shapes.   I hoping I can get some direction on how to make things better.   Right now not exactly sure what to do and I'm not getting a corrected 40mm.   I'm sure there's some tilt, but not getting the typical axial or radial patterns at the edge, so not sure what to do.

I took more images last night, until around 12:30am when I started to drop frames.  I think I need to install the V4 64b beta of SGP to fix this.    Still pretty cold, I think when I stopped it was around 4F again, but that's neither here nor there.   I started using the multi-star facility in phd2 and had a flat line with the occasional blip, most of the night even thought it was pretty breezy here, and at least according to the sky report, seeing was horrible.

Terri


Bill Long
 

You should work to get any tilt out before going much further with AP on the field performance of the Stowaway. I had to do this with my 16200, as I mentioned. Which is 36mm diagonal.


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Terri Zittritsch <theresamarie11@...>
Sent: Friday, February 12, 2021 7:57 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars
 

Hi Bill, I don't want to argue with you on what's inferred versus what it actually says.  The fact that it says APS-C works well doesn't really imply that the specification of  a 40mm corrected circle is somehow not to be counted on.  A 40mm corrected image circle only leaves 1.5mm on the corners, so almost full frame.   Depending on what APS-C system you have,  those require a significantly smaller image circle of 27mm or so (Canon).    

And just to be clear, I'm trying to understand what's going on, versus complaining (no need to defend anyone's honor).  In any case, getting a frame from one of my friends Eldorado star party images to compare star shapes.   I hoping I can get some direction on how to make things better.   Right now now exactly sure what to do and I'm not getting a corrected 40mm.   I'm sure there's some tilt, but not getting the typ. axial or radial patterns at the edge, so not sure what to do.

I took more images last night, until around 12:30am when I started to drop frames.  I think I need to install the V4 64b beta of SGP to fix this.    Still pretty cold, I think when I stopped it was around 4F again, that that it's either here nor there.   I started using the multi-star facility in phd2 and had a flat line with the occasional blip, most of the night even thought it was pretty breezy here, and at least according to the sky report, seeing was horrible.

Terri


Roland Christen
 

Shorten the distance between compressor and camera chip. 1, 2 or 3mm will make things better. Having too much distance will make it worse.

Rolando



-----Original Message-----
From: Terri Zittritsch <theresamarie11@...>
To: main@ap-ug.groups.io
Sent: Fri, Feb 12, 2021 9:57 am
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars

[Edited Message Follows]

Hi Bill, I don't want to argue with you on what's inferred versus what it actually says.  The fact that it says APS-C works well doesn't really imply that the specification of  a 40mm corrected circle is somehow not to be counted on.  A 40mm corrected image circle only leaves 1.5mm on the corners, so almost full frame.   Depending on what APS-C system you have,  those require a significantly smaller image circle of 27mm or so (Canon).    

And just to be clear, I'm trying to understand what's going on, versus complaining (no need to defend anyone's honor).  In any case, getting a frame from one of my friends Eldorado star party images to compare star shapes.   I hoping I can get some direction on how to make things better.   Right now not exactly sure what to do and I'm not getting a corrected 40mm.   I'm sure there's some tilt, but not getting the typical axial or radial patterns at the edge, so not sure what to do.

I took more images last night, until around 12:30am when I started to drop frames.  I think I need to install the V4 64b beta of SGP to fix this.    Still pretty cold, I think when I stopped it was around 4F again, but that's neither here nor there.   I started using the multi-star facility in phd2 and had a flat line with the occasional blip, most of the night even thought it was pretty breezy here, and at least according to the sky report, seeing was horrible.

Terri


M Hambrick
 

Hi Terri & Bill

I am interested in this discussion because I also have a 92 mm f6.65 Stowaway, and I also have a 16200 camera that I want to use for imaging with the Stowaway.  I presume Bill that by 16200 you mean a SBIG STXL 16200 camera.

Terri - Could you post a screen shot of what your triangular stars look like ?

Bill - What exactly did you have to do to eliminate the tilt in your imaging train ? Do you also have a 92TCC (or 92FF) ? For whatever it's worth, George commented to me that my STXL16200 camera is a lot of weight to attach to the Stowaway.

Both - There was another discussion thread recently concerning the locking screws on the Doveloc adapters that come with the 92 mm Stowaways. You need to examine your 92TCC adapters and if you are seeing any little indentations in the groove as shown in the attached photo it means that the lock screws are not forcing the 92TCC flush against the surface of the rear of the Doveloc adapter at the rear of the focuser barrel.

In order to seat properly, the tapered tip if the lock screws must be in contact with the tapered section of the groove in the 92TCC. In my opinion, there is a design or manufacturing flaw in the Doveloc adapters, and the lock screws are located too close to the back face of the Doveloc adapter by about 0.030". The tips of the lock screws should not dig into the base of the groove at all, but if they do, it should be right at the corner where the tapered section and the base of the groove intersect.

You can do a workaround by rounding off the tips of the lock screws with a file, but I am thinking about re-drilling and tapping another set of holes for the lock screws in my Doveloc adapter.

Mike


Bill Long
 

My camera is an FLI ML16200. I fixed it's tilt with a piece of aluminum foil. I have the 92TCC and 92FF. The field is perfect on the 92FF but you need to reduce the spacing 1-3mm for the 92TCC to dial it in. I had no problems with my camera and wheel on the Stowaway. Not enough space for an OAG so either use a guide scope or go unguided.

I'm not sure what you mean about the locking screws. I have seen no problems using mine at all. What was your experience?


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of M Hambrick <mhambrick563@...>
Sent: Saturday, February 13, 2021 7:47 PM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars
 
Hi Terri & Bill

I am interested in this discussion because I also have a 92 mm f6.65 Stowaway, and I also have a 16200 camera that I want to use for imaging with the Stowaway.  I presume Bill that by 16200 you mean a SBIG STXL 16200 camera.

Terri - Could you post a screen shot of what your triangular stars look like ?

Bill - What exactly did you have to do to eliminate the tilt in your imaging train ? Do you also have a 92TCC (or 92FF) ? For whatever it's worth, George commented to me that my STXL16200 camera is a lot of weight to attach to the Stowaway.

Both - There was another discussion thread recently concerning the locking screws on the Doveloc adapters that come with the 92 mm Stowaways. You need to examine your 92TCC adapters and if you are seeing any little indentations in the groove as shown in the attached photo it means that the lock screws are not forcing the 92TCC flush against the surface of the rear of the Doveloc adapter at the rear of the focuser barrel.

In order to seat properly, the tapered tip if the lock screws must be in contact with the tapered section of the groove in the 92TCC. In my opinion, there is a design or manufacturing flaw in the Doveloc adapters, and the lock screws are located too close to the back face of the Doveloc adapter by about 0.030". The tips of the lock screws should not dig into the base of the groove at all, but if they do, it should be right at the corner where the tapered section and the base of the groove intersect.

You can do a workaround by rounding off the tips of the lock screws with a file, but I am thinking about re-drilling and tapping another set of holes for the lock screws in my Doveloc adapter.

Mike


Roland Christen
 

For a 16200 camera you definitely want to use the Field flattener. It has a much bigger corrected field than the telecompressor. Don't even think about using the telecompressor.

Roland



-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 9:47 pm
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars

Hi Terri & Bill

I am interested in this discussion because I also have a 92 mm f6.65 Stowaway, and I also have a 16200 camera that I want to use for imaging with the Stowaway.  I presume Bill that by 16200 you mean a SBIG STXL 16200 camera.

Terri - Could you post a screen shot of what your triangular stars look like ?

Bill - What exactly did you have to do to eliminate the tilt in your imaging train ? Do you also have a 92TCC (or 92FF) ? For whatever it's worth, George commented to me that my STXL16200 camera is a lot of weight to attach to the Stowaway.

Both - There was another discussion thread recently concerning the locking screws on the Doveloc adapters that come with the 92 mm Stowaways. You need to examine your 92TCC adapters and if you are seeing any little indentations in the groove as shown in the attached photo it means that the lock screws are not forcing the 92TCC flush against the surface of the rear of the Doveloc adapter at the rear of the focuser barrel.

In order to seat properly, the tapered tip if the lock screws must be in contact with the tapered section of the groove in the 92TCC. In my opinion, there is a design or manufacturing flaw in the Doveloc adapters, and the lock screws are located too close to the back face of the Doveloc adapter by about 0.030". The tips of the lock screws should not dig into the base of the groove at all, but if they do, it should be right at the corner where the tapered section and the base of the groove intersect.

You can do a workaround by rounding off the tips of the lock screws with a file, but I am thinking about re-drilling and tapping another set of holes for the lock screws in my Doveloc adapter.

Mike


Roland Christen
 

Sorry, I misread the camera type. I was thinking of the FLI 6803 camera. The 16200 will work with both flattener and TCC. (Late night at work, not enough sleep, 14 hour days)

Rolando



-----Original Message-----
From: Roland Christen via groups.io <chris1011@...>
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Sat, Feb 13, 2021 10:20 pm
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars

For a 16200 camera you definitely want to use the Field flattener. It has a much bigger corrected field than the telecompressor. Don't even think about using the telecompressor.

Roland



-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 9:47 pm
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars

Hi Terri & Bill

I am interested in this discussion because I also have a 92 mm f6.65 Stowaway, and I also have a 16200 camera that I want to use for imaging with the Stowaway.  I presume Bill that by 16200 you mean a SBIG STXL 16200 camera.

Terri - Could you post a screen shot of what your triangular stars look like ?

Bill - What exactly did you have to do to eliminate the tilt in your imaging train ? Do you also have a 92TCC (or 92FF) ? For whatever it's worth, George commented to me that my STXL16200 camera is a lot of weight to attach to the Stowaway.

Both - There was another discussion thread recently concerning the locking screws on the Doveloc adapters that come with the 92 mm Stowaways. You need to examine your 92TCC adapters and if you are seeing any little indentations in the groove as shown in the attached photo it means that the lock screws are not forcing the 92TCC flush against the surface of the rear of the Doveloc adapter at the rear of the focuser barrel.

In order to seat properly, the tapered tip if the lock screws must be in contact with the tapered section of the groove in the 92TCC. In my opinion, there is a design or manufacturing flaw in the Doveloc adapters, and the lock screws are located too close to the back face of the Doveloc adapter by about 0.030". The tips of the lock screws should not dig into the base of the groove at all, but if they do, it should be right at the corner where the tapered section and the base of the groove intersect.

You can do a workaround by rounding off the tips of the lock screws with a file, but I am thinking about re-drilling and tapping another set of holes for the lock screws in my Doveloc adapter.

Mike


ROBERT WYNNE
 

This is a tricky geometry to machine precisely. The work around is to round off the tip of the sharp screw to allow deeper positioning of the screw without touching or touching off on the barrel yet while applying a compression load against the mating surfaces. -Best, Robert

On 02/13/2021 7:47 PM M Hambrick <mhambrick563@...> wrote:
 
 
Hi Terri & Bill

I am interested in this discussion because I also have a 92 mm f6.65 Stowaway, and I also have a 16200 camera that I want to use for imaging with the Stowaway.  I presume Bill that by 16200 you mean a SBIG STXL 16200 camera.

Terri - Could you post a screen shot of what your triangular stars look like ?

Bill - What exactly did you have to do to eliminate the tilt in your imaging train ? Do you also have a 92TCC (or 92FF) ? For whatever it's worth, George commented to me that my STXL16200 camera is a lot of weight to attach to the Stowaway.

Both - There was another discussion thread recently concerning the locking screws on the Doveloc adapters that come with the 92 mm Stowaways. You need to examine your 92TCC adapters and if you are seeing any little indentations in the groove as shown in the attached photo it means that the lock screws are not forcing the 92TCC flush against the surface of the rear of the Doveloc adapter at the rear of the focuser barrel.

In order to seat properly, the tapered tip if the lock screws must be in contact with the tapered section of the groove in the 92TCC. In my opinion, there is a design or manufacturing flaw in the Doveloc adapters, and the lock screws are located too close to the back face of the Doveloc adapter by about 0.030". The tips of the lock screws should not dig into the base of the groove at all, but if they do, it should be right at the corner where the tapered section and the base of the groove intersect.

You can do a workaround by rounding off the tips of the lock screws with a file, but I am thinking about re-drilling and tapping another set of holes for the lock screws in my Doveloc adapter.

Mike


Bill Long
 

It's okay. I knew what you meant.

The field is really nice with a 16200 and the 92FF. I shot this with it:

https://www.astrobin.com/kz7pe3/J/?nc=user

I did have some data from the 92TCC in this as well, but most was with the 92FF.

At some point I need to reprocess that data to get rid of some gradients I just now noticed....


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Roland Christen via groups.io <chris1011@...>
Sent: Saturday, February 13, 2021 8:23 PM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars
 
Sorry, I misread the camera type. I was thinking of the FLI 6803 camera. The 16200 will work with both flattener and TCC. (Late night at work, not enough sleep, 14 hour days)

Rolando



-----Original Message-----
From: Roland Christen via groups.io <chris1011@...>
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Sent: Sat, Feb 13, 2021 10:20 pm
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars

For a 16200 camera you definitely want to use the Field flattener. It has a much bigger corrected field than the telecompressor. Don't even think about using the telecompressor.

Roland



-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-ug.groups.io
Sent: Sat, Feb 13, 2021 9:47 pm
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars

Hi Terri & Bill

I am interested in this discussion because I also have a 92 mm f6.65 Stowaway, and I also have a 16200 camera that I want to use for imaging with the Stowaway.  I presume Bill that by 16200 you mean a SBIG STXL 16200 camera.

Terri - Could you post a screen shot of what your triangular stars look like ?

Bill - What exactly did you have to do to eliminate the tilt in your imaging train ? Do you also have a 92TCC (or 92FF) ? For whatever it's worth, George commented to me that my STXL16200 camera is a lot of weight to attach to the Stowaway.

Both - There was another discussion thread recently concerning the locking screws on the Doveloc adapters that come with the 92 mm Stowaways. You need to examine your 92TCC adapters and if you are seeing any little indentations in the groove as shown in the attached photo it means that the lock screws are not forcing the 92TCC flush against the surface of the rear of the Doveloc adapter at the rear of the focuser barrel.

In order to seat properly, the tapered tip if the lock screws must be in contact with the tapered section of the groove in the 92TCC. In my opinion, there is a design or manufacturing flaw in the Doveloc adapters, and the lock screws are located too close to the back face of the Doveloc adapter by about 0.030". The tips of the lock screws should not dig into the base of the groove at all, but if they do, it should be right at the corner where the tapered section and the base of the groove intersect.

You can do a workaround by rounding off the tips of the lock screws with a file, but I am thinking about re-drilling and tapping another set of holes for the lock screws in my Doveloc adapter.

Mike


Terri Zittritsch
 

Thank you Roland, This is what I am looking for.   Any thoughts on the best way to have some adjustment here?   The 92TCC is an 2.7" internal thread.   What I'd like to do is build something 3-4mm shorter and have several spacers to fine tune the size versus trying another shot in the dark.   I don't see any spacers spacers on your site for this.  I can ask that the other end of the adapter gets a longer thread and put some external spacers there.   I think this is the first step, and then I can work on any tilt in my system.
I checked out my friends Stowaway images when using a Canon Ra with my reducer, and he has much better star shape, farther to the edge of the frame, but i can see the beginnings of triangular stars in one corner.   Again I wonder if adding the filter, which extended my distance another 1 mm (3mm thick  Chroma filters) exacerbated the issue

There was a thread, I think back in December, after I had already ordered my adapter where it came to light that the back focus spacing isn't the same for all sensor sizes.   You had indicated at the time you were going to publish updates but don't see anything different on the website.   Did you ever get around to this?    It would be good to publish this along with the spec's so we know how to build our adapters, or alternatively always recommend building 3nm shorter and buying spacers.

I will be trying me TEC next, with the QuatTCC flattener/reducer to see how they work at full frame.


best,
Terri


On Sat, Feb 13, 2021 at 01:10 PM, Roland Christen wrote:
Shorten the distance between compressor and camera chip. 1, 2 or 3mm will make things better. Having too much distance will make it worse.
 
Rolando


Bill Long
 

I build all my PP adapters minimum length and use spacer kits to dial them in. Baader sells m68 spacers and shims that work nicely. At the minimum, make the adapter 3mm shorter than needed.


From: main@ap-ug.groups.io <main@ap-ug.groups.io> on behalf of Terri Zittritsch <theresamarie11@...>
Sent: Sunday, February 14, 2021 8:43 AM
To: main@ap-ug.groups.io <main@ap-ug.groups.io>
Subject: Re: [ap-ug] Stowaway with full frame sensor, 92TCC and triangular stars
 
Thank you Roland, This is what I am looking for.   Any thoughts on the best way to have some adjustment here?   The 92TCC is an 2.7" internal thread.   What I'd like to do is build something 3-4mm shorter and have several spacers to fine tune the size versus trying another shot in the dark.   I don't see any spacers spacers on your site for this.  I can ask that the other end of the adapter gets a longer thread and put some external spacers there.   I think this is the first step, and then I can work on any tilt in my system.
I checked out my friends Stowaway images when using a Canon Ra with my reducer, and he has much better star shape, farther to the edge of the frame, but i can see the beginnings of triangular stars in one corner.   Again I wonder if adding the filter, which extended my distance another 1 mm (3mm thick  Chroma filters) exacerbated the issue

There was a thread, I think back in December, after I had already ordered my adapter where it came to light that the back focus spacing isn't the same for all sensor sizes.   You had indicated at the time you were going to publish updates but don't see anything different on the website.   Did you ever get around to this?    It would be good to publish this along with the spec's so we know how to build our adapters, or alternatively always recommend building 3nm shorter and buying spacers.

I will be trying me TEC next, with the QuatTCC flattener/reducer to see how they work at full frame.


best,
Terri


On Sat, Feb 13, 2021 at 01:10 PM, Roland Christen wrote:
Shorten the distance between compressor and camera chip. 1, 2 or 3mm will make things better. Having too much distance will make it worse.
 
Rolando


Haydon Burns
 

Hello Terri,

I had always been visual but within the past few months have been getting into taking photos.  So take this for what it's worth but hopefully it adds to the discussion because someone can correct any of the below that is incorrect.  But in recently trying to trouble shoot a backfocus issue, I took away the following from what I had read (whether wrong or right).

All sensor sizes would be on the same focal plane and reach focus at the same distance, but the larger the sensor, the more critical spacing becomes.

Two telescope samples (even of the same model) may not have the exact same f/ratio due to subtle differences in the glass/optics from one sample to another.  I think this may be why people start with the theoretical required backfocus spacing and adjust with shims, spacing etc. for their particular setup (that and for other reasons such as the additional requirements due to adding filters).  

If adding spacers shims to the 92TCC, a heads up that there is no lip at the base of the threads for a spacer or shim to push up against.  I tried to add some in experimenting only to find that the spacer slipped over the thread and kept on going.  A bone headed move on my part.  :)


Terri Zittritsch
 
Edited

On Sat, Feb 13, 2021 at 10:47 PM, M Hambrick wrote:
Terri - Could you post a screen shot of what your triangular stars look like ?
Hi Mike, here you go, this is a small area of an uncalibrated frame (60mp ff sensor).  Just to be clear, this is not in the corner and is well into the frame.   Centers seem well corrected as I expected since I get good shapes with my asi1600.    I get the same in all corners, about the same amount.   I think I have to get rid of the triangles before I can do any tilt adjustment.  
 I get the same deformations/dimpling in the reducer like you're seeing.    I'm getting little dimples in the grooves wherever it's tightened down in approximately the same place in the groove.  It seems solidly attached as I checked with this heavier camera/2" filter wheel and OAG (4 lbs) although not heavy compared to some ccd setups.     I did have to tighten up my focuser just a smidge, as I could get some movement.  I used the large stainless hex screw on top and just maybe 20-30% of a turn the slop went away.

 


Good luck on your setup.

Terri