A0-8T backfocus spacing

Hello, I am a bit confused here.....Do you measure the back focus to the CCD chip or to the A0-8T lens? Does the AO-8T have its own backfocus from the lens paddle to the CCD chip? thanks

 

Backfocus is measured from the CCD chip to the e.g. flattener, or primary objective, primary mirror etc and not the AO-8 tilt paddle which being a plain, flat glass disk has no "focussing power" for want of a better expression, of its own.

But, as with any plain glass element in a converging beam path (light cone) such as a glass filter, or in the AO-8, the tilt plate, refraction of the light beam as it passes through the plate pushes the focal point further out and the general rule is to add ~1/3 the thickness of the glass element to the backfocus length.

For the AO-8 the backfocus used up when installed in the focal path is the mechanical thickness of the body plus adapter plates etc minus 2mm, i.e. when working out your BF distances the body of the AO-8 will appear optically 2mm thinner than it's mechanical thickness.

Hope that has not confused you more...See page 9 of the AO-8 manual where the actual dimensions are stated:

https://diffractionlimited.com/wp-content/uploads/2016/04/ao8manual.pdf

William.

 

Ok so does this mean I cannot use a reducer with the AO unit? The guys at OPT told me I basically cannot. I have the Celestron Edge 9.25 with Astro-Physics 27TVPH .75reducer and get a messed up star field or quite a bit of optical distortion. I was also informed that you can us ethe AO device with the EdgeHD 11" with reducer. I'd like to be able to use the AO because it is alot like magic when guiding. SO can I use this with a reducer on my 9.25 or do I need to get a different telescope such as the EdgeHD 11"" with reducer?

 

In front of my reducer? That just sounds ridiculous and impractical. How am I supposed to do that? So what kind of telescope exactly is this AO unit supposed to work with? Does it work with any kind of practical setup? When it was designed there must be some kind of optical system that works with this, what is it? Otherwise this thing is just a really expensive paper weight.

 

I'm just curious as to why you want to use an AO unit to hopefully increase your resolution then use a focal reducer to reduce your resolution? Perhaps I'm missing something.

 

Joshua my plan was just to use the optical guiding aspect of the AO to help with random guiding errors and not to increase resolution. The point of the focal reducer is to get to the F7.5 speed and have a wider FOV and then use the AO to help "cancel out" random guiding errors that my guidescope can't account for. I have to use the guidescope because MaxIm DL has a major glitch when trying to calibrate the drive in the AO tab, therefore MaxIm DL cannot activate the mount properly when the AO reaches it's tip tilt limit so I just use a guide scope with PHD2 and use the AO to cancel out any flexure, mirror shift etc..., I am not trying to increase resolution. That can only be done by changing the image scale which the AO doesn't do, infact this type of AO is basically only a high speed optical guider and as a "true" AO that will distort the mirror based on a diffraction sample generated by a false star projection like "real" AO devices do. It sounds like you haven't used one of these before based on your question but then again I could be missing something here as I have about 3 months experience with an SCT.

 

Good to hear Doug! Hopfully the guidestar faded issue gets fixed too!

 

I see what you are saying, however there is a repeatable condition where I'll start guiding on a good star and as soon as I start the sequence the star will fade even if I still see it in the track box. I have to stop he sequence and restart guiding and usually this fixes it but it would be nice to not have to do all that.

 

Doug...any word on that beta release? will the update be free to use MaxIm users?