2" and 1.25" focuser sizes - what's the difference?

[HunterGeo]

Hi all,

I recently found a Sky-Watcher 1000mm/127mm Newtonian reflector on eBay; it sold for $100 with an Alt-Az mount. I was thinking I'd replace my ED80 with it (and use the ED80 as a guidescope, both sitting on my HEQ5 Pro).

However, I was concerned about a particular matter, and the telescope sold while I was still trying to decide.

Specifically, the telescope had a 1.25" focuser (as opposed to the ED80's 2" focuser). As I wanted the telescope for astrophotography, I already have a 2" t-mount for my camera.

I was wondering what the actual difference would be between a 1.25" and a 2" focuser (other than the diameter, of course!). Would the smaller hole mean a reduction in light-gathering speed? Would I have to image for longer with a 1.25" to get the same exposure than I would with a 2" focuser? Or is it merely a matter of standards and wouldn't have made a difference?

Thanks in advance for your thoughts,
Dave

[2stroke]

You probably won't fill the whole sensor giving you a circle image of the sky in the middle of the image. Think line of site, really I have never tried it only thinking what might happen. Not to burst your bubble but i wouldn't bother, try getting your self a 8" f5 and pref 8" f4 as i don't think you will gain any light gathering power really over the ed80 with such a small cheaply built newt. We sold our last skywatcher/saxon 8" f5 for $150 here lol which would beat that thing seven ways to sunday.

[HunterGeo]

Thanks for that advice, Jay. I'll hold off on downgrading my telescope, then. :)