why is my aperture opening wider than f/5.6?

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Not having seen more than a couple of l.f. lenses I'm not sure if this is anything unusual but I've just acquired a horseman 75mm lens in a seiko shutter and the aperature blades open up quite a bit past the f5.6 marking on the barrell. Looking at the markings on the aperature I can open up to 5.6 and the blades inside are not fully open. The lever to change the aperature can then be turned a bit more to open it up all the way. Does this sound like the aperature markings are off and i should consider 5.6 to be fully open and perhaps the true 5.6 marking to be more like f/8? Or is this completely normal? My other lens opens up just a tad past the 5.6 marking on the barrel but this one opens up considerably so i am a bit suspicious.

thanks linda

-- linda wessel (peanutcoffee@hotmail.com), June 14, 2000


The aperture indicator has probably just got bent over to one side a bit. They're fairly flimsy little metal arms that stand proud of the shutter enough that they can easily be bent or twited out of true. It doesn't take much. I pushed mine out of shape just shoving it into its little foam rubber "nest" a bit roughly the other day.

-- Pete Andrews (p.l.andrews@bham.ac.uk), June 14, 2000.


Assuming the lens/shutter hasn't been damaged as suggested in the previous post, I'd offer this thought. When the shutter is calibrated to the lens it is fixed at a certain position, which may not be the same for each lens (but very close.) Therefore, there may be some "play" when the lens is wide open. I have seen and own several new lens' like this and when someone like Steve Grimes mounts a lens in a shutter, he calibrates the apperature ring, which results in a symptom like you have described.


-- Ephemera1 (pcaluori@hotmail.com), June 14, 2000.

Many shutters are made as to be somewhat universal, and can be fitted to different lenses. It may be made to operate down to 4.5 or so (like many press lenses). If you want to check it, install a known lens on your camera, and set the aperture to 5.6 (or 8), and aim your camera at a brightly lit wall, and use your hand held meter to read off the center of your ground glass and note the reading. Now install the 75mm lens, and set the aperture to the same f stop as the first lens, and again read the value from the center of the ground glass. If the readings are the same, then its no problem. If they are different, you can now 'calibrate' the new lens in this same fashion. This is how replacement shutter/aperture assemblies are calibrated for use on a lens.

-- Ron Shaw (shaw9@llnl.gov), June 14, 2000.

I have a 47 mm lens on which the positioner moves half an inch passed the f5,6 marking and several other lenses with some "play" too. So I would think what you see is normal. In fact, once the aperture blades have reached the nominal opening, a wider opening has no effect on the ammount of light passing through.

-- Paul Schilliger (pschilliger@smile.ch), June 14, 2000.

Perhaps the aperature marking scale is not the correct scale for your lens. Seiko is not a common shutter for newly manufactured lenses, and your lens might be in an older shutter with a scale for some other lens. I'd ask Calumet photo. They are quite familiar with the Horseman products, and I think, used to be the exclusive importer.

-- Charlie Strack (charlie_strack@sti.com), June 14, 2000.

Ron's right on this one. A standard shutter size is used for many lenses. The aperture opens to a standard maximum size which is greater then f/5.6 for your lens. But the mechanical elements of the lens, and its optical design, won't let you use this additional opening, so the manufacturer calibrates the opening for your particular lens. How far past "maximum" the aperture opens varies greatly from lens to lens, particularly if the manufacturer used a generously sized shutter. For some focal lengths, different manufacturers will use different sized shutters. In the 180-210 range, Rodenstock often uses a #1 where Schneider uses a #0.

-- Glenn C. Kroeger (gkroeger@trinity.edu), June 14, 2000.

All five of my LF lenses (modern Schneiders and Nikons) do this to some extent so it isn't unusual and doesn't indicate a defect in the lens or the shutter (at least I hope it doesn't - if it does I'm in real trouble).

-- Brian Ellis (bellis@tampabay.rr.com), June 15, 2000.

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