I found out tonight for the first time in a long time (I forgot!), that I can't get prime focus through my Canon 350D with it T-Mounted onto my SkyWatcher 300mm (12 inch) Dob. No matter what combination of threaded rings on the Crayford focuser, it just wouldn't get to prime focus. Anyone have experience and a solution to this?

Seanie.

Hi Seanie,

You might not have enough 'in focus' (if that's the word) i.e. the camera is not close enough to prime focus even when the focuser is racked all the way in.

Michael.

That's it alright Michael. I thought of even sawing the end of the barrel enough to get it in, but I'd have to shave the outside of the upper half of the barrel of the T-adapter. That's all I can think of to make it fit!

Seanie.

I had the same problem with my 8" newt years ago, I ended up replacing the focuser with a low profile job.
This is an example of what you'll need www.firstlightoptics.com/skywatcher-focu...rayford-focuser.html 
Usually comes with an extension tube so you can still use it visually.

Thanks John, I'll check that out. That one pretty much looks like mine, only it's shallower when reeled all the way in. Why it wasn't standard to begin with, I don't know.

I think they tend to use standard/cheaper focusers on most dobs/newtonians and these are really only suitable for visual use, they will not back focus enough to bring a focused image onto a camera sensor. The good thing about replacing the focuser with one suitable for photography is that you will (usually) spend an extra few quid on fine tuning focusing e.g. 10:1 or better, and this helps quite a bit both in visual and photo use.