Meade TeleXtender (or Powermate) focus point / parfocal-nes

[riklaunim]

So the description for those 4-element extenders stat that they (almost) don't change the focus point with/without the element in the path. How does it look in the real life? Do they add only small focus point change (or none)?

I'm thinking about the possibility to put 2x-3x TeleXtender onto the camera nosepiece (chasing planetary nebulas) - after the Celestron OAG. If it won't change the focus point a lot, then I wouldn't have to fight with focus on the guide cam.

[Merlin66]

Good question!

I regularly use the powermates for solar imaging but I've never honestly measured the focuser position with and without the unit.

If the "barlow" lens was positioned correctly inside focus by the shoulder/ T thread adaptor then at least in theory it is possible. You'd have to watch for interference between the OAG prism and the "nose" of the powermate.....

If I ever get the chance to set up the Ha scope again (!!) I'll confirm the measurements.

[E621Keith]

I found there is a slight change in focus position, but it's very small compared to a barlow. I didn't measure how much, but it was at most half a turn on a 10:1 focuser.