Vixen R200SS back focus

[graham.hobart (Graham stevens)]

I am considering this scope a nice fast f4 W.F newt.
I have some concerns about the available back focus and my imaging rig though.
The specs describe scope back focus as 72.5mm.
I have an SBIG STT8300 which is described as back focus 17.5mm
plus an FWG-8G filter wheel described as 54.06mm
and then an AO8-T described as 51.3mm back focus (=122.86 mm together)
Add into this mix a coma corrector and a Moonlite focuser upgrade and I have doubts it will all fit?
I am adding all the SBIG stuff together- is this correct?
If so I will not be able to fit it all in - is that so?

Is there any way around this?

Thanks for any help
Graham

[Visionoz (Bill)]

Nope!

Cheers
Bill

Originally Posted by graham.hobart

I am considering this scope a nice fast f4 W.F newt.
I have some concerns about the available back focus and my imaging rig though.
The specs describe scope back focus as 72.5mm.
I have an SBIG STT8300 which is described as back focus 17.5mm
plus an FWG-8G filter wheel described as 54.06mm
and then an AO8-T described as 51.3mm back focus (=122.86 mm together)
Add into this mix a coma corrector and a Moonlite focuser upgrade and I have doubts it will all fit?
I am adding all the SBIG stuff together- is this correct?
If so I will not be able to fit it all in - is that so?

Is there any way around this?

Thanks for any help
Graham

[Shiraz (Ray)]

lack of back focus is a big issue with fast Newtonians.

Found one reference saying that the distance from CC to the focal plane should be 55mm. Sorry, but I don't think that any of the SBIG gear fit if that is the case. The only option I can think of would be to use an RCC1 CC and modify the scope by moving the mirror up and fitting a larger secondary, but that would be a lot of work and even then, I think that you would only be able to fit in the FW, not the AO.

[roughy (Mark)]

Hi Graham
Have a look at another thread on this forum - "Initial test of SX AO at F4". There is some discussion about the benefit of AO for wide field.

[graham.hobart (Graham stevens)]

Yeah, looked at that and realised it was folly.
Just was pissed off with other scopes lack of cooperation and looking for alternatives. But now is all happy as have had several days kicking the other scope into submission and feel now that the Man Vs Optics equation is sort of skewed in my favour. Time will tell.
Remember folks, they are optical tools, not strange objects from Planet ZZ9 plural Z Alpha.
So as tools they can be tooled with, (with the right tools!)
Alliteratively
Graz