trouble focusing

[sinbad40]

Hi all,

So on my 80Ed i attached a 533C, didn't put a reducer/flattener on, just wanted to do focus and a few shots as i wanted to test out other things and sort the cabling out, didn't have much time with clouds passing etc.  I couldn't get it to focus, just looked like bad vignetting and pushed over to one side, couldn't focus on anything.  I didn't think i would have needed any back focus with the travel the focus gives, but could be wrong. Will need to try again, with more time.

 

[LaurenceT]

3 hours ago, sinbad40 said:

Hi all,

So on my 80Ed i attached a 533C, didn't put a reducer/flattener on, just wanted to do focus and a few shots as i wanted to test out other things and sort the cabling out, didn't have much time with clouds passing etc.  I couldn't get it to focus, just looked like bad vignetting and pushed over to one side, couldn't focus on anything.  I didn't think i would have needed any back focus with the travel the focus gives, but could be wrong. Will need to try again, with more time.

 

Did you attach any spacers to the 533mc?

[sinbad40]

Hi, I didn't use any spacers thinking i could get the focal plane with the scope travel focusing.  I know if using a reducer/flattener etc its around 55mm.

I have read around a 70mm image extender may be needed to go straight through the scope

 

Edited July 3, 2022 by sinbad40

[LaurenceT]

Just add the M42-48 , the 16.55mm and the 21mm spacers and you should be able to focus. I'm as new to this as you but I think that focus tube travel is independent of back focus requirements of cameras.

[rickwayne]

The simplest way to figure this out is to just set the acquisition software to do live-capture video, and then hold the camera up behind the telescope, pointed at a daylit scene. Move the camera closer or farther away to focus. Note the approximate distance; duplicate that with whatever hardware you need. You only have to estimate it to within a couple cm since the focuser travel will let you zero in once you've got it set up somewhere in the neighborhood.