Autofocus PHD2 Guide Scope Camera / OAG


I have a guide scope/camera and would like to be able to perform autofocus on both the main imaging camera, as well as periodic autofocus on the guide scope camera’s ASCOM focuser. I am using PHD2 for guiding.

I have not seen anything about auto-focusing guide camera, is this possible ?

My optical train is Scope, main ASCOM focuser, OAG (with it’s own ASCOM focuser) , rotator, filter wheel, main camera.

It would be great to be able to autofocus my OAG after main focuser autofocus, after filter wheel changes.

If this is already possible, please direct me to any appropriate documentation…


Hey Tim,

I’m confused: Given you’re using an OAG aren’t your main camera and guidecam’s focus basically locked? I know that there could be small differential changes due to contraction in the OAG it self, but I doubt that would ever be enough to affect guiding.

So, once you have locked in the right spacing for your guidecam so that it is parfocal with your imaging cam, focusing the imaging cam will also focus the guidecam.


I have a ASI174MM mono as a guide camera for my OAG and an ASI1600MM Cooled imaging camera. It’s important to have the same distance from the prism to the OAG camera sensor as from the prism to the image Camera sensor. pHD2 doesn’t require absolute pin-point stars for guiding and in fact, they shouldn’t be. I’ve got an motorized focuser for my SCT and with any focus of my filters (LRGB and NB), pHD2 works perfectly.

As Steve mentioned, a small change in focus has no affect on the guiding of your mount by pHD2.