A Question Regarding Waterhouse Stops

[c.d.ewen]

I've been making waterhouse stops for a number of barrel lenses. These are lenses that originally had such stops, but none were present at the time I acquired them. Determining the size of the opening for a desired f/stop, with the highest degree of accuracy possible. is important. I've been wondering if an assumption I've made is valid.

Soldered inside the barrel of a better quality lens, there is usually a pair of disks. The disks hold the inserted stops perpendicular to the lens axis. My question is this: with no inserted stop, is the opening of the soldered disks the appropriate opening for the indicated maximum opening for the lens?

In other words, has anyone ever come across an f/8 lens, for example, that had an f/8 waterhouse stop, and that stop's opening was smaller than the soldered disks' opening?

Charley

[Mark Woods]

Yes

[c.d.ewen]

Yes

Well, poop! There goes another bad assumption.

Was it smaller by much?

Charley

[polyglot]

Depends on the lens design. Plenty easy for the waterhouse guides inside the lens to be nowhere near the actual optical path (some of them have a very small waist where a shutter+aperture could go), which means that the size of the slots is irrelevant.

For some designs, the simple D = f / f-number will be perfectly accurate but that's not true at least for telephoto and retrofocus lenses. Perhaps some others too, I'm not sure.