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| Getting correct (55mm) distance between field flattener and Camera CCD with ZWO EFW inbetween the two... Hello everyone, I'm new to the forum so please forgive my lack of knowledge as I am relatively new to astrophotography & setting up equipment. I wonder if anyone could help with this... I am trying to get the correct distance between my 0.8x field flattener and the Altair 183m camera with a ZWO 8 position EFW fitted with 1.25" filters inbetween the flattener and the camera. Now I do have a 1.25" nose piece and the piece that this slides into. These two pieces assembled had M42 male each side, which fitted perfectly between the camera and the EFW, meaning (to my mind at least) that all I needed was an M48 female to M42 male adapter ring. Sadly though, now knowing that the EFW needs to be as close to the camera as possible to reduce any halo effect, I can't make use of this setup anymore, or can I? If I can't, how would I go about achieving the correct distance? I have a Starwave Ascent 80ED field flattener/reducer 0.8x (M48 male) , a ZWO 8 position EFW (20mm depth, M42/T2 female each end) fitted with 1.25" filters and an Altair 183m camera (M42/T2 female). If anyone could advise, I would be most grateful. Thanks, Shaun |
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You need a male to male M42 adaptor (a.k.a gender changer). The order of insertion would thus be: corrector -> spacers (if needed) -> FW -> male to male adaptor -> camera The camera flange to sensor distance is 17.5mm and the FW optical depth is 20mm (+1/3 filter thickness), so let's say 38 mm all told. There should be around 12mm spacing required and thus ample space for a M42 to M42 gender changer. |
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andrea tasselli: Thanks for your response Andrea. That makes sense now. I've checked the flange to sensor distance on Altair's website and it is actually 12.5mm, so that would be 12.5mm + 20mm + 1/3 * 1.9 + 2mm (could be 1.5mm) M42 male to male connector, m48 female to M42 male connector (1.5 - 2mm), so that would be approx 36mm, so would need approx 19mm M48 extension, give or take a mm for not knowing the extra added due to the M42-M42 & M42-M48 ! Just looking at a set of extension tubes now, they come in a set of 3 5 7 10 12 15 20 30mm, so a 12 & a 7mm should do the job  .Just out of curiosity, how accurate does this have to be? I mean, if it was +/- a milimeter out from 55mm, would that be an issue? Regards, Shaun |
