Re: To guide or not, that is the question


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?



Brian Valente


Brian Valente

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