IMPORTANT!!!! QHY600M - 020002 Adapter - CFW3-M FW back focus question.

I was about to get Precise Parts to make expensive custom adapter for the following:

QHY600M camera: 17.5mm
QHY 020002 camera adapter supplied with QHY600M: 4mm or 6mm <========== ???????
CFW3-M filter wheel: 20.5mm
Optec Sagitta OAG: 31.75mm
TEC 0.9x Focal Reducer Corrector (FRC): total back focus 115mm

According to QHY 020002 camera adapter specification, it says the spacing is 6mm.


But according to the following image below:


The QHY 020002 adapter spacing is 4mm. Is it because of the 2mm lip of 020002 adapter is buried inside the CFW3-M/L filter wheel giving the effective back focus of 4mm?

Which back focus for QHY 020002 adapter when attaching to CFW3-M/L filter wheel is correct: 4mm or 6mm?

Please respond ASAP as I am getting ready to order custom adapter from Precise Parts which can take 3 weeks to get it.

Thank you very much,
« Last Edit: March 10, 2021, 11:16:31 AM by topboxman »

Please provide an answer. I cannot order custom adapter from Precise Parts without knowing for sure.

I remember about six months ago, your adapter diagrams showed QHY 020002 adapter back focus of 6mm and now it shows 4mm back focus without any explanation of the change. That's why I am extremely careful before spending over $200 for custom adapter.

Thank you,



The thickness is indeed 6mm. But when you use CFW, the value is 4mm. So you should calculate the value with 4mm.

Best Regards!

Thank you ZY.

That's exactly what I wanted to know. Yes, I am using CFW3-M filter wheel and I noticed the effective back focus for QHY 020002 adapter is 4mm but I wanted to be sure.