CKemu Posted September 20, 2022 Share Posted September 20, 2022 So I have the Skywatcher 100ED Field Flattener ("FF" from now on) and the following imaging train: FF > M48 to M54 Adapter (2mm)* > OAG (24mm) > Filter Wheel (22mm) > Baader Filters (0.7mm) > ATIK 490EX (13mm) *this is on order from FLO, so currently unable to test this setup. 61.7mm total Required back focus is 55mm ...fuuuuuuu-dge. 6.7mm which I can't really shave off, but I have an imaging circle of 40mm and the chip diagonal is 15.97mm, do you think I will get away with it? I see posts with people sweating over 1mm, but they're often DSLR users! Perhaps this is something that can't easily be answered, gosh I wish there was a tool to simulate this m'larky! Link to comment Share on other sites More sharing options...
newbie alert Posted September 20, 2022 Share Posted September 20, 2022 What oag are you using? Link to comment Share on other sites More sharing options...
tomato Posted September 20, 2022 Share Posted September 20, 2022 That does seem a lot of mm for your OAG, I use a ZWO item, 16.5mm thickness, which would just about make it. Link to comment Share on other sites More sharing options...
CKemu Posted September 20, 2022 Author Share Posted September 20, 2022 59 minutes ago, newbie alert said: What oag are you using? 33 minutes ago, tomato said: That does seem a lot of mm for your OAG, I use a ZWO item, 16.5mm thickness, which would just about make it. I'm using the ATIK OAG for their EFW2. Link to comment Share on other sites More sharing options...
tomato Posted September 20, 2022 Share Posted September 20, 2022 I guess you could screw it all together then see just how much of the sensor FOV is unusable (if any). Link to comment Share on other sites More sharing options...
The Lazy Astronomer Posted September 20, 2022 Share Posted September 20, 2022 FYI, don't count the filter thickness in your backfocus, instead add 1/3 the filter thickness on to your required backfocus. Doesn't really help much though as you'll still be ~5.8mm out. But worst case is you may need to look for a thinner OAG, or perhaps a Starlight Express filter wheel with a built in OAG. Frustratingly for you, it may require more £££ to be spent, but not a horrific outcome (your title had me thinking something had gone badly wrong!) 1 Link to comment Share on other sites More sharing options...
CKemu Posted September 21, 2022 Author Share Posted September 21, 2022 11 hours ago, tomato said: I guess you could screw it all together then see just how much of the sensor FOV is unusable (if any). Think that's the plan, take a few shots and check out the stars afterwards - for a hobby that requires patience, I am terrible at having patience and hate wasting clear nights though! ha 10 hours ago, The Lazy Astronomer said: FYI, don't count the filter thickness in your backfocus, instead add 1/3 the filter thickness on to your required backfocus. Doesn't really help much though as you'll still be ~5.8mm out. But worst case is you may need to look for a thinner OAG, or perhaps a Starlight Express filter wheel with a built in OAG. Frustratingly for you, it may require more £££ to be spent, but not a horrific outcome (your title had me thinking something had gone badly wrong!) The ZWO OAG is quite thin, no idea if it would attach to my ATIK EFW2 - will have to research, but that would save a good chunk of space. More £££, well I can cope with a few more if it gets me in to a position where I can use the full sensor width - but I shall test this once the part comes and "waste" a clear night. The title stems from frustration more than actual disaster! 1 Link to comment Share on other sites More sharing options...
CKemu Posted September 22, 2022 Author Share Posted September 22, 2022 It is never easy eh...........manufacturing companies need to create a "BASIC" set of mechanical conventions and tolerances,.....because DEAR FUDING LORD my patience is being worn thin right now. Link to comment Share on other sites More sharing options...
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