[E_ri_k (Erik)]

Originally Posted by acropolite

The Sharpsky focus controller and motor has excellent compensation capabilities.

Thanks, I have had a look at their website, only unsure on how to mount it?

Originally Posted by Chris85

As I understand it, yes, that's the way it should work. I guess you'd refocus with filter changes, but maybe not if you use offsets? I've yet to try temp focusing myself, but I do have one of these on the way http://www.usb-foc.us/ to help me get started.

Cheers,
Chris

Thanks Chris, I'll have a look at their site I can set offsets for my filters. Would be interested to hear how it works out for you.

Originally Posted by PRejto

The only way temperature compensated focusing can work is if the change in focus is linear over the range of temperature you hope to image in. And, the only way to find out is to actually graph the focus change vs temperature to confirm. Many scopes are not linear. I know that FocusMax V.4 has a wizard that will plot focus position vs temperature over many hours, and I think the Optec controller FocusLynx will also do something similar. The other critical issue is the location of the temperature probe. Microtouch puts the probe inside the controller and that is utterly useless (stupid! actually). Optec offers a kit with an external probe that will operate a Microtouch motor but only if you also use the Optec hub. Of course, it will operate with Optec and Starlight Instrument hub controllers/bipole motors.

Peter

EDIT: This is rather interesting. http://www.innovationsforesight.com/...ime-autofocus/

Scroll down to this section: "Focus versus time analysis using SharpLock"

You can see how non-linear most of the plot is. Of course, every excursion would mean that temp-compensated focusing would fail. Naturally every system is different so you might find your scope linear enough. I think most people using temp. compensated focusing do so as an aid to focusing fewer times but not as a replacement for focusing.

By the way, if you are talking about your TOA150 it is possible to fit an ONAG-XT and a TOA-67 flattener with some cameras. The back focus is just long enough. I've done exactly that with my TEC180 and have been using Sharplock/FocusLock software for incredible autofocusing. With this system temperature simply doesn't matter. You can image all night and never focus.

Thanks for the info. Good point about the change having to be linear, I didn't think of that......So it is still necessary to adjust the focus either way, and this is not a way to eliminate it completely. Thats good to know.

I did have an ONAG, not the XT version though. I sold it because I wasn't confident it would be a good match for the TOA. I never had a chance to try the SharpLock software with my old scope. Thats amazing that you never have to re focus! If I had the spare cash I'd probably invest in one again, but with the low exchange rate, I'd e up for a few $K when I add in a focuser upgrade....

Erik