Extenders, filters, vignetting.

[Pixies]

I'm wanting to start dipping my toes into EEVA with SharpCap and live-stacking, and so have just purchased a new ASI585MC camera. I've been doing some test runs in daylight using my old ST80 and find I need some additional extension to get focus.

I can put the camera with 1.25" adapter into the diagonal and just get focus (inwards) but it looks awfully unstable.

I've tried using a 40cm T2 extender directly attached to the visual back but that's not long enough. I had this lying around in a box of nick-nacks in my Astro man-drawer:

Now, I can get more T2 extension and reach focus that way. But it's lacking any way to rotate the camera without unscrewing, plus there's nowhere to place a filter ( I'd want to use a Baader Semi-APO at least). I think there are various attachments to allow a rotator and insert a filter in the chain, but at some expense.

Another option is this (from FLO):

Which would attach to the camera using the T2 thread allow me to insert it into the scope's visual back using the 1.25" barrel - which can also take a 1.25" filter. However, I'm not sure if having the small filter at that distance would cause vignetting?

The final and simplest option would be the more prosaic 1.25" extenders and use the 1.25" adapter on the camera (with the filter), but I can't find any long enough.

 

Any suggestions? I guess this is all bread-and-butter to you AP bods, but it's all new to me,

 

Cheers.

 

[pipnina]

Quote

I've tried using a 40cm T2 extender directly attached to the visual back but that's not long enough.

That's one long extender! 😜

I found on my frac that they have a lot of backfocus, I presume because most are designed with reducers and diagonals in mind.

I think a good test to see if you are going to see vignetting is to look down the scope, and if you can see the whole camera sensor from the corner of the objective lens, you're not going to see any vignetting!

I think you can find camera rotators (Maybe like this one, but this is bigger than M42 thread https://www.firstlightoptics.com/williams-optics-focusers/william-optics-camera-angle-rotator-for-25-m63-focuser.html) so that could be an option here.

I think for the modest size of the IMX585 31mm filters should be perfectly fine, so something like a filter drawer should work fine here: https://www.firstlightoptics.com/zwo-accessories/zwo-2-filter-drawer-m42-m48.html. This is, again, a bit big but you get the idea!

Adding items like these to fit your current extension might bring you into focus, depending on how much further out you need to be?

Hope this helps a bit.