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I'm sure this is just one of many hundreds of posts about correct spacings on here - I think I've just about got it but I need to confirm a couple of things with folks who have more experience than me on these matters.
My scope is a Skywatcher Evostar 80ED-DS Pro - one which I'm sure anyone here is familiar with and needs little introduction. I'm using the accompanying field flattener/reducer, which requires 55mm of back focus.
The off axis guider I plan to use is an OVL Off Axis Guider - it is thin enough that in combination with my camera I should have the required back focus provided the connecting T-adapter is thin enough.
My camera is a Canon 550D (mod), which as far as I'm aware will occupy 46.5mm of back focus.
My question is, what would be the best way to connect the Canon to the OAG? Puzzlingly it seems the OAG has a 42mm screw-ring on the camera side, which I don't have an adapter for. Do these exist? Are there any thin models available such that I meet my back focus requirement?
If there are any other issues with what I'm suggesting please let me know. It's always easier to nail it first time than faff around with ordering adapters only to discover they're the wrong size.
Funny thing - I have an ASI1600 + EFW and am connecting to SW coma corrector which requires 55mm spacing. The camera is 6.5mm the EFW is 20mm, total 26.5, so 28.5mm spacer required - sound correct hopefully?
But the suppllied spacers are 21mm and 16.5mm which doesnt help (and doesnt seem correct even for a colour ASI1600 with no EFW) There is also a 11mm female/female adapter and a very short 1.5mm male/male adapter, so I guess I could use the 11mm F/F followed by the 1.5mm M/M + the 16.5 giving 29mm but this seems a bit complicated!
Just wondering what other folk do - I cant be the only one with this problem. Any thoughts please?
Atik OAG. It was bought to go with the Atik EFW2 (all fixing screws are provided). It is in its original box and is complete except for one 4mm T-2 spacing ring (for the helical focuser) - the 7mm and 15mm rings are shown attached. (The reason for the missing 4mm ring is that this got used for spacing in my Esprit 120 rig - it works perfectly, and I ain't taking it out ). You need to check that the OAG, wheel and camera spacings will fit within your specified field-flattener spacing requirements. I didn't check! As such, the OAG was never used.
I will ship it for £110. Any takers at £100? Bank transfer preferred.
I have a revelation (GSO) coma corrector that I use on my 130 pds with a Canon 1000d. I have noticed that I am still getting some coma. My question is, do I need a spacer between the corrector and the T ring. I can't find any definite information on this but I read somewhere you need 75mm between the rear element and the camera sensor