Star Tails

[Buckrogers]

I have 3 m42 spacers, 8mm, 25mm and 45mm. Go with the 25?

[Chuckwagon]

The 25mm would be my guess. Since there is a little spacing inside the reducer body from the threads to the lens, that spacing will be subtracted from the 25mm length. It looks like the space inside the reducer is about 8-10mm. If it's 10mm, then you'd have the 12.5mm of the camera plus the 15mm of the spacer (25 - 10 for the offset of the reducer lens) to get you around 27.5mm. Or pretty close to it. Check the spacing yourself to see if it looks like the lens of the reducer will end up around 28mm from the camera sensor, but I think the 25 is a good start point. A couple mm either side of 28mm shouldn't be a big issue.

Chuck