I've got a 150mm claron coming that I picked up off Ebay. I already have a #0 shutter that currently holds the cells for a 127mm Xenar. Obviously the F/stops won't match up but can I just do some math?

If my math is right:

127/labelled f/stop = aperture size.

150/aperture size = new f/stop

So an indicated F/16 would be F/19 with the 150mm lens. F/11 would be F/13. F/22 would be F/26. Sort of makes that digital light meter make sense.

The lens uses 35.5mm filters? Anybody know of a source for a setup ring to something more mainstream?