Lens board with 39mm hole

[eatfrog]

I bought a MPP lens board (it was cheap..) for the Microtechnical Mk 8 and was surprised to see that it had a 39mm hole. As far as I had understood, the #1 is 41.6mm and after some research I have found two things, first off that there was a bunch of these lens boards made so it is not an one off. One of the "kit lenses" probably used this sized lens board, does anybody know more about this?

Second, I see that there are a lot of Copal 1 lens boards for sale with a 39mm hole. Isn't this too small? Can this be used with a Copal 1 shutter?

The hole is not threaded, i have measured it to be pretty exactly 39mm, maybe a tenth of a millimeter larger, maybe two.

Thankful for any information you guys might have about this!

Kind regards,
Henri Toivonen

[Dan Fromm]

#1 shutters' rear tubes are threaded M39x1, so will fit in a 39 mm hole. The recommended hole size is 41.6 mm. This is to allow the retaining ring's centering ridge to grip the inside of the hole and position the shutter.

If you want to mount a #1 on a board with a 39 mm hole, put the shutter's rear tube through the hole and screw the retaining ring on the tube with the centering ridge facing away from the board.

[Andy Eads]

39mm is the standard Leica screw mount thread size. Many enlarger lenses use that thread. Perhaps that board held a lens for close up work.