How do I utilize the new Pegasus OAG with ASCOM focuser?

First, I apologize for not asking my question clearly last time, so here goes a second try:

I see there is a new Pegasus product coming out soon, that is an OAG with a built in ASCOM motorized focuser of it’s own. This seems like a product I really want to use.

How can I use that new product with SGP / PHD2 ?

My understanding is that PHD2 makes its own exclusive connection to it’s guide camera, and since it does not have autofocus capability, there is an issue trying to use SGP’s autofocus for this new product in a sequence. Since SGP currently does not have the ability to connect and disconnect PHD during a sequence, the guide camera can not pass data to SGP for autofocus.

(The use case for this is that my filter wheel is not in my guide camera/OAG’s optical path (it is after the OAG), and thus any focus offset in my filters will cause my guide camera to go out of focus (after autofocusing the main camera). My main ASCOM focuser is between the telescope and the OAG.

There is significant focus difference between some of my filters, that cause the guide camera to be far enough out of focus to make guiding impossible. I realize that some believe that out of focus guiding is not harmful or even good, that may be true for minute out of focus conditions, but the offsets I have found with my filters, have proven to cause focus difference be to drastic enough to prevent decent guiding at all.


There is not currently a great way to do this. I have a similar issue with my Optec Sagitta (OAG + Focus Motor) but my filters are “close enough” to parfocal.

The basic mode of operation would be to apply some offset to the OAG focuser just like is done for a normal filter wheel. As far as “who” does this that’s a different question. On one hand you could argue it’s up to the auto guider as it already has a connection to the camera that it will be focusing. On the other you could argue that it’s up to the imaging software as it has a connection to the imaging camera and knows when the filter is changing.

I’m not really sure what the right solution is here to be honest. It would be mostly trivial to create something that handles this without being in either application as well. Basically an application that connects to the filter wheel as well as the focuser and has the offsets in place. When a filter change is made it adjusts the focuser.


Given the potential mechanical, electrical connections, control etc pit-falls of having a second focuser, I can’t help thinking that a less problematic solution to your problem might not be simply to replace the least parfocal of your filters (hopefully an LRGB set) for ones that are more closely matched to any more exensive NB filters you might have.

At the least I would certainly look at the cost differences.

Clear skies


I have one filter that’s far away from my other filter’s focus points, Baader set vs IDAS LP filter.

I set my OAG focus to the best compromise between the two, it’s been like this for about eight years now with no problems and great guiding.

I don’t understand the problem that Pegasus are trying to solve here. If the difference is just too large I’d definitely stay away from an additional piece of kit and the complexity in getting it working reliably if I could solve the problem permanently by changing filters.

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