To guide or not, that is the question


Jeffc
 

A question for those of you more experienced with AE mounts...

Is "classical auto guiding" required if the mount has absolute encoders, and an APPM model is created?   (I.e. auto-guiding with a guidescope, or OAG.)

Ray once told me:   "If your guide camera has to adjust the position of the mount, then your  mount, then your image is already damaged by the photons that went into the wrong pixel.  It is too late."

With the AE on the Mach2, I have not used a guidescope since receiving the mount a few months ago.   The results look great if I create and use a pointing model.   (I did notice that without a pointing model imaging closer to the horizon (iirc like under 30 degrees up) the stars are elongated.   I believe this is atmospheric refraction.

Am I missing something?   
I just find the idea of messing with the OAG (in my case) to be a) more stuff to get going/manage and b) potentially cause further image damage if something goes awry with guiding.

And if there is a need for the guide camera, what is the purpose when AE+APPM is used?

AE + APPM + Guide camera?
-- Or --
AE + APPM + no need to guide?

thx
-jeff


 

Hi Jeff

I think it depends :)

for a mach2 and perhaps a modest focal length/image scale, you could easily get away with just a model and no guiding

As image scale gets more fine, everything becomes more challenging

Right now i am bringing up our CDK20 with image scale of 0.54" on a 1600 with encoders 

i have opted to go with "bump guiding" (as Roland calls it) where i'm using PHD2 to do 3 sec exposures, wait 10 seconds, repeat, Even with a completely terrible guide camera and problematic setup, i'm still getting around 0.3-0.4" guiding. Aside from some setup issues, things like scope flexure become major issues.

however, earlier i was doing widefield on that same mount with an 80mm refractor and about 2.6" image scale and was able to easily do 15 minute unguided subs

  

On Tue, Jul 6, 2021 at 8:59 AM Jeffc <jeffcrilly@...> wrote:
A question for those of you more experienced with AE mounts...

Is "classical auto guiding" required if the mount has absolute encoders, and an APPM model is created?   (I.e. auto-guiding with a guidescope, or OAG.)

Ray once told me:   "If your guide camera has to adjust the position of the mount, then your  mount, then your image is already damaged by the photons that went into the wrong pixel.  It is too late."

With the AE on the Mach2, I have not used a guidescope since receiving the mount a few months ago.   The results look great if I create and use a pointing model.   (I did notice that without a pointing model imaging closer to the horizon (iirc like under 30 degrees up) the stars are elongated.   I believe this is atmospheric refraction.

Am I missing something?   
I just find the idea of messing with the OAG (in my case) to be a) more stuff to get going/manage and b) potentially cause further image damage if something goes awry with guiding.

And if there is a need for the guide camera, what is the purpose when AE+APPM is used?

AE + APPM + Guide camera?
-- Or --
AE + APPM + no need to guide?

thx
-jeff



--
Brian 



Brian Valente


Jeffc
 

> modest focal length/image scale, you could easily get away with just a model and no guiding

Oh.. yes.   There's probably a FL limit on this depending on mount size.  (I was thinking under 1000mm.)
I've been experimenting with the 12" ACF and reducer at about 1900mm with promising results.

Good point about "bump guiding" ... I'll have to keep that in mind.



On Tue, Jul 6, 2021 at 9:13 AM Brian Valente <bvalente@...> wrote:
Hi Jeff

I think it depends :)

for a mach2 and perhaps a modest focal length/image scale, you could easily get away with just a model and no guiding

As image scale gets more fine, everything becomes more challenging

Right now i am bringing up our CDK20 with image scale of 0.54" on a 1600 with encoders 

i have opted to go with "bump guiding" (as Roland calls it) where i'm using PHD2 to do 3 sec exposures, wait 10 seconds, repeat, Even with a completely terrible guide camera and problematic setup, i'm still getting around 0.3-0.4" guiding. Aside from some setup issues, things like scope flexure become major issues.

however, earlier i was doing widefield on that same mount with an 80mm refractor and about 2.6" image scale and was able to easily do 15 minute unguided subs

  

On Tue, Jul 6, 2021 at 8:59 AM Jeffc <jeffcrilly@...> wrote:
A question for those of you more experienced with AE mounts...

Is "classical auto guiding" required if the mount has absolute encoders, and an APPM model is created?   (I.e. auto-guiding with a guidescope, or OAG.)

Ray once told me:   "If your guide camera has to adjust the position of the mount, then your  mount, then your image is already damaged by the photons that went into the wrong pixel.  It is too late."

With the AE on the Mach2, I have not used a guidescope since receiving the mount a few months ago.   The results look great if I create and use a pointing model.   (I did notice that without a pointing model imaging closer to the horizon (iirc like under 30 degrees up) the stars are elongated.   I believe this is atmospheric refraction.

Am I missing something?   
I just find the idea of messing with the OAG (in my case) to be a) more stuff to get going/manage and b) potentially cause further image damage if something goes awry with guiding.

And if there is a need for the guide camera, what is the purpose when AE+APPM is used?

AE + APPM + Guide camera?
-- Or --
AE + APPM + no need to guide?

thx
-jeff



--
Brian 



Brian Valente


 

tubes are going to be less problematic re: flexure than truss in my experience

i did do unguided for quite some time with the CDK17 and could image 5 min subs pretty reliably - that's somewhere around 2500mm

just an example:



On Tue, Jul 6, 2021 at 11:00 AM Jeffc <jeffcrilly@...> wrote:
> modest focal length/image scale, you could easily get away with just a model and no guiding

Oh.. yes.   There's probably a FL limit on this depending on mount size.  (I was thinking under 1000mm.)
I've been experimenting with the 12" ACF and reducer at about 1900mm with promising results.

Good point about "bump guiding" ... I'll have to keep that in mind.



On Tue, Jul 6, 2021 at 9:13 AM Brian Valente <bvalente@...> wrote:
Hi Jeff

I think it depends :)

for a mach2 and perhaps a modest focal length/image scale, you could easily get away with just a model and no guiding

As image scale gets more fine, everything becomes more challenging

Right now i am bringing up our CDK20 with image scale of 0.54" on a 1600 with encoders 

i have opted to go with "bump guiding" (as Roland calls it) where i'm using PHD2 to do 3 sec exposures, wait 10 seconds, repeat, Even with a completely terrible guide camera and problematic setup, i'm still getting around 0.3-0.4" guiding. Aside from some setup issues, things like scope flexure become major issues.

however, earlier i was doing widefield on that same mount with an 80mm refractor and about 2.6" image scale and was able to easily do 15 minute unguided subs

  

On Tue, Jul 6, 2021 at 8:59 AM Jeffc <jeffcrilly@...> wrote:
A question for those of you more experienced with AE mounts...

Is "classical auto guiding" required if the mount has absolute encoders, and an APPM model is created?   (I.e. auto-guiding with a guidescope, or OAG.)

Ray once told me:   "If your guide camera has to adjust the position of the mount, then your  mount, then your image is already damaged by the photons that went into the wrong pixel.  It is too late."

With the AE on the Mach2, I have not used a guidescope since receiving the mount a few months ago.   The results look great if I create and use a pointing model.   (I did notice that without a pointing model imaging closer to the horizon (iirc like under 30 degrees up) the stars are elongated.   I believe this is atmospheric refraction.

Am I missing something?   
I just find the idea of messing with the OAG (in my case) to be a) more stuff to get going/manage and b) potentially cause further image damage if something goes awry with guiding.

And if there is a need for the guide camera, what is the purpose when AE+APPM is used?

AE + APPM + Guide camera?
-- Or --
AE + APPM + no need to guide?

thx
-jeff



--
Brian 



Brian Valente



--
Brian 



Brian Valente


Marcelo Figueroa
 

Since I received my Mach 2 I am not using guiding, it works perfect with my Esprit 100 on exposures of about 8 to 10 minutes (although because of my light pollution I usually use about 4 min).
 
It is very satisfying to no longer hear the annoying beep of PHD2 when it loses the guide star on a clear night. However there is a drawback, the guiding also acts as a cloud detector, and if it gets cloudy the session is automatically aborted. But if you are using only the modeling you can perfectly well spend the night photographing clouds :D.
 
 
PS: for really long exposures, more than 30 minutes, then you really need guiding.


Dean Jacobsen
 

On Tue, Jul 6, 2021 at 08:59 AM, Jeffc wrote:
A question for those of you more experienced with AE mounts...
 
Is "classical auto guiding" required if the mount has absolute encoders, and an APPM model is created?   (I.e. auto-guiding with a guidescope, or OAG.)
 
Ray once told me:   "If your guide camera has to adjust the position of the mount, then your  mount, then your image is already damaged by the photons that went into the wrong pixel.  It is too late."
 
With the AE on the Mach2, I have not used a guidescope since receiving the mount a few months ago.   The results look great if I create and use a pointing model.   (I did notice that without a pointing model imaging closer to the horizon (iirc like under 30 degrees up) the stars are elongated.   I believe this is atmospheric refraction.
 
Am I missing something?   
I don't think you are missing anything Jeff. 

As others have said, it might depend on your focal length.  I have been doing unguided imaging with the Mach2 for a year now at 400mm and 540mm focal length and I don't feel the need to use a guide scope any more for those focal lengths.  I have seen what Roland has been able to do at longer focal lengths with the Mach2 for longer exposure times than I have been using.  I am sure that the other AE enabled AP mounts would have similar or better performance. 

This is a recent unguided example at 400mm focal length:

https://www.astrobin.com/5cyci6/
 
--
Dean Jacobsen
Astrobin Image Gallery - https://www.astrobin.com/users/deanjacobsen/


Edward Beshore
 

Hi Dean

Nice image. If I closely examine the hi-res version, I see the square stars, meaning that while you are undersampled (totally understandable given your imaging setup) it also means the tracking is very good.

ed


Dean Jacobsen
 

Hi Ed, thanks for the kind words.  

I have been extremely happy with the Mach2 and going unguided with my short focal length setup has worked very well for my situation.  Easy to set up.  Running a 3 line APPM model centered on the declination of the night’s target (I set up and break down the rig each night) is quick and can be completed as the optics are cooling and it is getting dark.  

I have been using AP mounts for almost 20 years and the mounts and software just keep getting better.
--
Dean Jacobsen
Astrobin Image Gallery - https://www.astrobin.com/users/deanjacobsen/