How feasible is tandem imaging with AP1100 with or without AE and 2 1000mm refractors with ~0.8"/px image scale?


Shitij Bhargava
 

Hi all,

I am a purely nomadic imager for now and have been using fast reflectors so far because they are cheaper and faster (quite important for cloudy PNW), but something or the other keeps changing/shifting during roadtrips making my actual imaging time much less than I would hope. So I am thinking about giving up on the cheaper aspect of my system for more stability in the setup, and just going with 2 TOA130NFB (assuming I can find them) in tandem on AP1100 (without AE for now) to still keep similar speed. I could use 2 mounts as well (have a Mach1), but it would be impossible to fit everything in my civic so would have to get a new car as well to make it work ;)

There are some threads on tandem imaging and possible issues with APCC model not being applicable to both scopes due to differential flexure, but has someone actually tried it with similar focal length/image scale and can share first hand experience? Would adding AE (when its available, hopefully this year) significantly improve the odds of making this setup successful and has somebody tried that? My intuition is that I would have to go unguided with this setup since guiding even with with an OAG in one scope would make corrections that may not be applicable to the other one.

Thanks,
Shitij


Kent Kirkley
 

Shitii

Tandem imaging at the same time is nearly impossible with 1000mm instruments.
Differential flexure will take place....even with the most robust mounting.
Add to that, you're already experiencing shift due to transportation.
Kent Kirkley
AP 1200GTO
AP Traveler
AP 160



-----Original Message-----
From: shitij.cse@...
To: main@ap-gto.groups.io
Sent: Fri, Jul 1, 2022 3:10 pm
Subject: [ap-gto] How feasible is tandem imaging with AP1100 with or without AE and 2 1000mm refractors with ~0.8"/px image scale?

Hi all,

I am a purely nomadic imager for now and have been using fast reflectors so far because they are cheaper and faster (quite important for cloudy PNW), but something or the other keeps changing/shifting during roadtrips making my actual imaging time much less than I would hope. So I am thinking about giving up on the cheaper aspect of my system for more stability in the setup, and just going with 2 TOA130NFB (assuming I can find them) in tandem on AP1100 (without AE for now) to still keep similar speed. I could use 2 mounts as well (have a Mach1), but it would be impossible to fit everything in my civic so would have to get a new car as well to make it work ;)

There are some threads on tandem imaging and possible issues with APCC model not being applicable to both scopes due to differential flexure, but has someone actually tried it with similar focal length/image scale and can share first hand experience? Would adding AE (when its available, hopefully this year) significantly improve the odds of making this setup successful and has somebody tried that? My intuition is that I would have to go unguided with this setup since guiding even with with an OAG in one scope would make corrections that may not be applicable to the other one.

Thanks,
Shitij


Roland Christen
 

I do tandem imaging all the time. I use refractors, which have stable optical - mechanical axes. As long as both scopes are securely fastened in their rings to one dovetail plate, the two refractors tend to track each other for at least 10 minutes with differential errors below the sub-arc sec level. SCTs and Newts are another ball of wax, and I would not count on them remaining stable.

Scopes I have tried this way are 92mm, 130GTX, 160GT, 175GT, and even 12" F8 and F12 Mak-Cassegrains with fixed mirrors, and the 305 Honders scopes. All these scopes have optics that are fixed in place with respect to their tube assemblies (no moving mirrors). With good modeling on the 1100/1600 AE mounts they can go unguided for at least 10 minutes.

In fact I have our 17" F8 astrograph do unguided imaging on a 1600AE mount for 5 and 10 minute exposures.
https://www.astrobin.com/hj4o7s/
https://www.astrobin.com/wqa9yw/

Rolando

-----Original Message-----
From: shitij.cse@...
To: main@ap-gto.groups.io
Sent: Fri, Jul 1, 2022 3:10 pm
Subject: [ap-gto] How feasible is tandem imaging with AP1100 with or without AE and 2 1000mm refractors with ~0.8"/px image scale?

Hi all,

I am a purely nomadic imager for now and have been using fast reflectors so far because they are cheaper and faster (quite important for cloudy PNW), but something or the other keeps changing/shifting during roadtrips making my actual imaging time much less than I would hope. So I am thinking about giving up on the cheaper aspect of my system for more stability in the setup, and just going with 2 TOA130NFB (assuming I can find them) in tandem on AP1100 (without AE for now) to still keep similar speed. I could use 2 mounts as well (have a Mach1), but it would be impossible to fit everything in my civic so would have to get a new car as well to make it work ;)

There are some threads on tandem imaging and possible issues with APCC model not being applicable to both scopes due to differential flexure, but has someone actually tried it with similar focal length/image scale and can share first hand experience? Would adding AE (when its available, hopefully this year) significantly improve the odds of making this setup successful and has somebody tried that? My intuition is that I would have to go unguided with this setup since guiding even with with an OAG in one scope would make corrections that may not be applicable to the other one.

Thanks,
Shitij

--
Roland Christen
Astro-Physics


Nathan Myhrvold
 

I have done tandem imaging with 600mm f/4 camera lenses - essentially 150mm refractors,  This is with QHY cameras with 5.94 micron pixels. The pixel scale is 2 arc/sec per pixel.  This was on a 10micron GM 1000 shot unguided, with a model made on one of the two OTA. 

It worked for me.  There are people on CloudyNights who use longer focal lengths in tandem rigs.

Flexure certainly could be an issue, but it wasn't for me.  I used the very heavy APM dual mount adapter, and my own custom made aluminum frame mounts that grip the lens with telescope rings so it is not all hanging from the lens foot. 

The pointing model was built for only one of these two scopes, which potentially would be another source of error.   But again, it wasn't that bad.

Note that a huge number of astrophotographers use a guide scope with active guiding (PHD2 or other) rather than using an OAG.   The idea of guiding based on a model from one scope and using it for both has the same issues that has - there could be flexure.  But in most cases these errors are quite tolerable, otherwise nobody would ever use a guide scope.

Mirror shift is potentially far more serious than flexure between two refractors.   The fundamental optics of a reflector are based on alignment.   The analogous situation for a refractor would be to have a shift in alignment between optical elements - which is also serious.   A well made OTA shouldn't be a problem, in my opinion.  But of course what matters is your actual set up, so ultimately you have to answer it empirically.


Ray Gralak
 

Hi Nathan,

I have done tandem imaging with 600mm f/4 camera lenses - essentially 150mm refractors, This is with QHY
cameras with 5.94 micron pixels. The pixel scale is 2 arc/sec per pixel. This was on a 10micron GM 1000 shot
unguided, with a model made on one of the two OTA.

It worked for me. There are people on CloudyNights who use longer focal lengths in tandem rigs.
It's not the mount but the rigidity of the mounting and the similarity of the scopes. As in your case, two of the same type of scope will have by far the best chance of working with a common model. And, auto-guided or not, the differential flexure between the scopes will limit the maximum exposure duration.

BTW, if this is your post on CN, there are a couple of things I would like to mention:

https://www.cloudynights.com/topic/829940-how-to-use-pointing-models-with-astro-physics-1100-encoder-mounts/

With plate solving and recentering in many apps, pointing correction is not as crucial as the tracking-rate correction.

APCC has two tracking rate algorithms: All-Sky, and Dec-Arc. The All-sky and Dec-Arc tracking models use the same data points collected by APPM. They coexist independently and simultaneously within APCC. APCC can use the All-Sky model for pointing correction and the All-sky *or* Dec-Arc model for tracking-rate correction. You can switch between them while tracking using a checkbox in APCC.

And, given the posts on CN, people posting there may not realize that APCC's Dec-Arc Tracking is not just an All-Sky model created from points near the same declination as other mounts might do. Dec-Arc Tracking is a new, optimized tracking algorithm independent of the All-Sky algorithm. Dec-Arc tracking does not use the standard pointing terms used in an All-Sky model because those pointing terms cannot cover all of the idiosyncrasies of every telescope.

Another attribute of APCC's pointing model is that it supports unlimited sky data points, while some mounts only support a limited count. Pointing/tracking-rate accuracy goes up roughly as the square root of the number of sky data points. An APCC user can thus create a dense All-sky model with unprecedented all-sky tracking accuracy using Dec-Arc Tracking, or a similarly dense model for one declination patch using the NINA plugin by Dale Ghent.

-Ray Gralak
(Author of APCC)


Roland Christen
 


BTW, if this is your post on CN, there are a couple of things I would like to mention:
I have never posted on Cloudy Nights.

Roland


-----Original Message-----
From: Ray Gralak <iogroups@...>
To: main@ap-gto.groups.io
Sent: Sat, Jul 2, 2022 10:05 am
Subject: Re: [ap-gto] How feasible is tandem imaging with AP1100 with or without AE and 2 1000mm refractors with ~0.8"/px image scale?

Hi Nathan,

> I have done tandem imaging with 600mm f/4 camera lenses - essentially 150mm refractors,  This is with QHY
> cameras with 5.94 micron pixels. The pixel scale is 2 arc/sec per pixel. This was on a 10micron GM 1000 shot
> unguided, with a model made on one of the two OTA.
>
> It worked for me. There are people on CloudyNights who use longer focal lengths in tandem rigs.

It's not the mount but the rigidity of the mounting and the similarity of the scopes. As in your case, two of the same type of scope will have by far the best chance of working with a common model. And, auto-guided or not, the differential flexure between the scopes will limit the maximum exposure duration.

BTW, if this is your post on CN, there are a couple of things I would like to mention:

https://www.cloudynights.com/topic/829940-how-to-use-pointing-models-with-astro-physics-1100-encoder-mounts/

With plate solving and recentering in many apps, pointing correction is not as crucial as the tracking-rate correction.

APCC has two tracking rate algorithms: All-Sky,  and Dec-Arc. The All-sky and Dec-Arc tracking models use the same data points collected by APPM. They coexist independently and simultaneously within APCC. APCC can use the All-Sky model for pointing correction and the All-sky *or* Dec-Arc model for tracking-rate correction. You can switch between them while tracking using a checkbox in APCC.

And, given the posts on CN, people posting there may not realize that APCC's Dec-Arc Tracking is not just an All-Sky model created from points near the same declination as other mounts might do. Dec-Arc Tracking is a new, optimized tracking algorithm independent of the All-Sky algorithm. Dec-Arc tracking does not use the standard pointing terms used in an All-Sky model because those pointing terms cannot cover all of the idiosyncrasies of every telescope.

Another attribute of APCC's pointing model is that it supports unlimited sky data points, while some mounts only support a limited count. Pointing/tracking-rate accuracy goes up roughly as the square root of the number of sky data points. An APCC user can thus create a dense All-sky model with unprecedented all-sky tracking accuracy using Dec-Arc Tracking, or a similarly dense model for one declination patch using the NINA plugin by Dale Ghent.

-Ray Gralak
(Author of APCC)







--
Roland Christen
Astro-Physics


Ray Gralak
 

Hi Roland,

BTW, if this is your post on CN, there are a couple of things I would like to mention:

I have never posted on Cloudy Nights.
Maybe you misread, but my response was to Nathan?

-Ray


Nathan Myhrvold
 

Yes, that was my post.    Honored to meet you (virtually).  I put the post on CN because there is a very active CN thread on 10micron models, but very little on AP.  I now realize that is because there is this forum.   Meanwhile the 10micron dedicated forum is pretty useless.   Sorry to be using a competitor as a point of reference, but it happens to be what I have used prior to getting my AP mount (1100 GTO AEL).

I am going to ask you some more detailed questions but I will them in a different post


Peter Bresler
 
Edited

Here is my setup on the 1200. I actually use the OAG on the Stellarvue for guiding the RH200.


Peter Bresler
 

A recent shot of M17 with the RH200.


Roland Christen
 

Hola Kau! That's a lotta wiring.

Rolando


-----Original Message-----
From: Peter Bresler via groups.io <PABresler@...>
To: main@ap-gto.groups.io
Sent: Sat, Jul 2, 2022 12:21 pm
Subject: Re: [ap-gto] How feasible is tandem imaging with AP1100 with or without AE and 2 1000mm refractors with ~0.8"/px image scale?

Here is my setup on the 1200.

--
Roland Christen
Astro-Physics


Karen Christen
 

Pretty cool little rollaway observatory shed thingy, Peter.  Don’t think I’ve seen one like that before.

Karen

AP

 

From: main@ap-gto.groups.io <main@ap-gto.groups.io> On Behalf Of Roland Christen via groups.io
Sent: Saturday, July 2, 2022 1:13 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] How feasible is tandem imaging with AP1100 with or without AE and 2 1000mm refractors with ~0.8"/px image scale?

 

Hola Kau! That's a lotta wiring.

 

Rolando

 

 

-----Original Message-----
From: Peter Bresler via groups.io <PABresler@...>
To: main@ap-gto.groups.io
Sent: Sat, Jul 2, 2022 12:21 pm
Subject: Re: [ap-gto] How feasible is tandem imaging with AP1100 with or without AE and 2 1000mm refractors with ~0.8"/px image scale?

Here is my setup on the 1200.


--
Roland Christen
Astro-Physics


--
Karen Christen
Astro-Physics


Dean Jacobsen
 

On Tue, Jul 5, 2022 at 08:39 AM, Karen Christen wrote:

Pretty cool little rollaway observatory shed thingy, Peter.  Don’t think I’ve seen one like that before.

Karen

Yes, a very innovative adaptation.  That is probably something I could adapt for my back yard.
 
--
Dean Jacobsen
Astrobin Image Gallery - https://www.astrobin.com/users/deanjacobsen/


Shitij Bhargava
 

Thank you for sharing your valuable experiences everyone. At least I know it is possible if I do things right, 10 minute exposures are good enough for me. Finding 2 TOA 130NFBs in stock and being gutsy enough to spend almost 20k on this setup to try it out would be the next challenge for me :)

I found this useful: https://www.swagastro.com/dual-imaging-set-up.html, as the article suggests an adjustment saddle would probably be a must to match the FOV but that version cannot support the weight of TOA 130NFB, so I might have to adjust my expectations and use smaller/lighter scopes instead


Bill Long
 

You'll want this one:

https://www.admaccessories.com/product/tgad-tandem-guiding-aiming-device-altaz-aiming-device-for-side-by-side-systems/



From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of shitij.cse@... <shitij.cse@...>
Sent: Thursday, July 21, 2022 5:17 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] How feasible is tandem imaging with AP1100 with or without AE and 2 1000mm refractors with ~0.8"/px image scale?
 
Thank you for sharing your valuable experiences everyone. At least I know it is possible if I do things right, 10 minute exposures are good enough for me. Finding 2 TOA 130NFBs in stock and being gutsy enough to spend almost 20k on this setup to try it out would be the next challenge for me :)

I found this useful: https://www.swagastro.com/dual-imaging-set-up.html, as the article suggests an adjustment saddle would probably be a must to match the FOV but that version cannot support the weight of TOA 130NFB, so I might have to adjust my expectations and use smaller/lighter scopes instead


Donald Gaines
 

Hi Shitij,

Here’s a link to a Cloudy Nights post where it was done with an Astro-Physics 1200 mount and Astro-Physics 160 F7.5 scope that may be of interest.

Don Gaines


On Friday, July 1, 2022, <shitij.cse@...> wrote:
Hi all,

I am a purely nomadic imager for now and have been using fast reflectors so far because they are cheaper and faster (quite important for cloudy PNW), but something or the other keeps changing/shifting during roadtrips making my actual imaging time much less than I would hope. So I am thinking about giving up on the cheaper aspect of my system for more stability in the setup, and just going with 2 TOA130NFB (assuming I can find them) in tandem on AP1100 (without AE for now) to still keep similar speed. I could use 2 mounts as well (have a Mach1), but it would be impossible to fit everything in my civic so would have to get a new car as well to make it work ;)

There are some threads on tandem imaging and possible issues with APCC model not being applicable to both scopes due to differential flexure, but has someone actually tried it with similar focal length/image scale and can share first hand experience? Would adding AE (when its available, hopefully this year) significantly improve the odds of making this setup successful and has somebody tried that? My intuition is that I would have to go unguided with this setup since guiding even with with an OAG in one scope would make corrections that may not be applicable to the other one.

Thanks,
Shitij


Shitij Bhargava
 

Thank you Bill and Don, I will check them out