30 HOLE LENS BOARD - What's the meaning?

[Kekhotep]

Hi,

I need a lens board for a lens, Keh lists boards like this, "CALUMET 4X5 (4X4) 30 HOLE LENS BOARD." What does this mean, is it mm? Is it equivalent to a copal size. My lens is a copal 1, that I know.

Advanced thank you

 

[paul ewins]

Yes, a 30mm hole. Although Copal 0, 1 and 3 are standard sized shutters the hole required can vary slightly depending on the particular flange or retainer used. Most retainers have a lip that is meant to sit in the hole in the lensboard, so the hole should be cut to fit the lip, not the thread on the shutter. That doesn't always happen so you get a variance in sizes and I guess KEH learned long ago that it is better to list the exact size of the hole rather than Copal 0 or 1 etc.

The hole for a Copal 0 is nominally 34mm and Copal 1 42mm so a 30mm hole is undersize for most modern shutters. It is possibly an Alphax 0.

 

[Kekhotep]

Thank you, that helped a lot paul

 

[Jim Jones]

The Alpex and Rapex #1 shutter had about 30mm shutter mounting threads. So did the #0 Compur and Ilex #0 Universal, Acme, and General. As Paul noted, some retaining rings were intended for larger holes. They still work with thread diameter holes. The old standard 4" square Lens boards are fairly easy to build up from 1/8" plywood, or mill down from 1/4 plywood. For temporary use, they can be improvised from mat board, foam core, or whatever else is available.