correct backspacing for OAG, FW and 1600mm

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correct backspacing for OAG, FW and 1600mm

Post by miwitte » Mon Apr 08, 2019 12:58 pm

I recently purchase a 8" EDGE-HD with .7x reducer and Moonlite focuser. The critical backspacing for the EDGE .7x reducer is 105mm

my setup is;

ZWO1600(6.5MM)->FW(20MM)->OAG(16.5MM)->Moonlite CHL(62MM)->Edge .7x reducer


5MM ZWO supplied Spacer



In looking at this i have 43 MM backspacing between my OAG(where it connects to moonlite) and ZWO 1600, but depending on how far up and down the OAG stalk is maybe 25-30MM backspacing between OAG and ASI 120. I think i may have missed the FW backspacing here when figuring things out. Do I need a larger spacer between the OAG and the ASi 120mm and if so how do i calculate what that spacer is. I cant find a measurement in the manual, however i do see that there is no FW in place in the instructions, the OAG is directly connected to camera and the 5mm spacer is needed for 12.5mm backspace cameras. With that said it would appear i need an additional 20mm spacer between the OAG and the ASI 120MM to take the FW backspacing into account.

If anyone has done this please let me know but it thin that seems right.

Or did i completely miss the mark and the OAG goes BETWEEN the FW and camera(that would actually make more sense now that i think about it)

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Re: correct backspacing for OAG, FW and 1600mm

Post by Sean.Wang » Mon Apr 29, 2019 10:17 am

Hi there
The sequence of 105mm back focus just like 55mm back focus solution. ... -55mm.html
Please take a look of mono camera setup.
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