Talk:Diaphragm

Need better sourcing

We need to find some references for this page. I see the definitions I original posted have drifted and the first two now seem to conflict (or at least the distinction is no longer clear).

My understanding (which is very possibly flawed!) is that a manual diaphragm is one that is continuously adjustable and does not have detents (presets). A preset diaphragm is a like a manual except that is has detents (presets). Also a preset may optionally have a 2nd ring for preview purposes and the preview ring operates like a manual diaphragm (i.e. continuously variable). I don't have any good authoritative sources to back this up at the moment. If anyone can source this, please do so and correct the definitions if needed.
Steevithak 13:57, 7 January 2012 (PST)

My recollection is that "preset" always referred the two-ring style of aperture control: one ring without detents that actually closes the diaphragm; the second with detents but unconnected to the diaphragm—just providing a stop, as you twisted the first ring to close down to shooting aperture. --Vox 14:32, 7 January 2012 (PST)

So, if you're correct, that means "2 Ring Preset" is a redundant phrase? I'll have some fix ups to do if that turns out to be the case. I'm having a hard time finding anything definitive. I've found one source so far, a 1961 Popular Science with a couple of paragraphs on the history of lenses. Seems to support your understanding (e.g. manual has detents, preset is manual + preview ring). Pop Sci Aug 1962
Steevithak 16:02, 7 January 2012 (PST)

Good reference, as that predates my adolescent perusing of PopPhoto mags, etc. by a decade. I don't think I've ever seen the phrase "2-ring preset," though. It's the second ring that "pre-sets" the desired shooting aperture.

The only really oddball alternative I know about is the early Canonflex lenses: They had a full auto diaphragm, but added a second ring for depth of field preview (I believe—never handled one in person)--Vox 20:36, 7 January 2012 (PST)