Orion TOAG, Canon DSLR and Altair Astro GPCAM AP0130

[rockinrome]

Hello all
I recently bought the Altair GPCAM1 AR0130 Mono to use as a guide camera.
My question is - is it OK to run without the CS "filter" installed.

Background:
I need to reach the correct back focus when using it with the Orion thin off-axis guider (TOAG) and the Altair Astro 1.0x field flattener.
The flattener needs an optimal 56mm from rear flange to camera optical plane which I can get with the provided attachment rings - basically replacing the T-adapter ring and then installing the TOAG. This is all OK.
That gives me 49mm from the centre of the TOAG to the camera optical plane which of course I need to make the same to the focal plane of the GPCAM.
From the centre of the TOAG to the top of the TOAG "stalk" is 43mm + 0.5mm for the base plate.
This is where the fun begins ........
The smallest I can get the AR0130 is without anything screwed in, thus removing the CS ring, giving me a distance to the focal plane of 7.5mm (according to specs.) I can then "shove" this onto the TOAG base and hold with a grub screw - all seems fine. This giving me a total distance of 51mm, so 2mm (approx.) too much.

<phew>
 

So ...... is that OK? Can I run guide camera in this way (without any window glass?)
I have thought about placing a 1mm ring/shim between TOAG and camera - making 50mm to camera focal plane.

Any thoughts people??

Thank you as always.
Clear skies.

Matthew

 

[rockinrome]

Your brain is a wonderful piece of kit ...... something has just occured to me that *may* solve my issues and this is ......
The measurement to the optical plane of the guiding sensor has to be taken from the centre of the OAG prism NOT simply the centre of the OAG unit - which should give me more to play with in the measurements.
However this distance must still match the camera focal distance - here the 49mm.

Thanks to all who looked.
MJ