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Hi WR,
The FF4 needs a lot of in-focus.
I just stopped down the aperature on my M90 to 30mm, took it outside, pointed it at the Sun and measured the focal point distance from the focuser(fully racked in) as ~135mm.
I worked out the FF4 needs another 15 to 20mm, so about 150 to 160mm of in-focus.
If your 102 has more than 160mm of back-focus then you are golden.
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