Extension Tubes Calculation

[Altocumulus]

Hi,

Has anyone married a William Optics WO P-F6A-GT102 with a ZWO camera (120MM USB2)? I'm a mite confused about how much extension I would need - possibly 60.95mm?

The F6A already comes with a 102 adapter, but I'll need a T2 to M48 adapter (6mm) to the camera. What's the expert opinion on the tube sizes to get to make up the difference.

This would be the first time of not using a wedge, and a straight camera connection on the OTA doesn't rest easy with a fully extended tube not providing a good back-focus, and the price of these things means I want to get it right first time......

[yobbo89]

the asi 120 is 12.5mm back focus,. the f6a gt102 is 54.8 mm, so you need 42.3 mm of extension.

i'll have to dig up some more info on the product.

[Altocumulus]

OK.

I went with a Baader adjustable extender.

Put the meerest smidgeon of lubricant on the thread and started to marry the extender to the 102 adapter, only for them to jam 2-3mm from the shoulder. Does anyone have a solution on how to complete the thread travel!

I'm currently trying a series of hot (50C) and cold (-20C) cycles to see if that will budge them, but not looking promising.
I've tried the other usuals, kitchen gloves etc.

If I can't screw on any further it'll not come off in a hurry, so the marriage is still useable as long as I can work out the correct measurement.

Grrrr!