Posted by Moose on February 23, 2003 at 01:39:08:
In Reply to: V ivatar lense posted by Bob Kaufmann on February 22, 2003 at 17:06:34:
Sounds like a preset lens. Since you are looking through the actual lens you are taking a picture with, on an Single Lens Reflex camera, the lens will have to stop down to control the amount of light that gets to the film, under most conditions (ie. sunny day). The more a lens closes down, the less light gets through and the harder it is to see through the lens. The idea is that you use the extra ring to set the aperture where you think it should be based on metering or guessing--let's say for example f8. Then you open up the lens to maximum aperture with the regular ring, to allow for easy focusing, since more light is allowed through the lens, when it is wide open. When you are ready to take your photo you turn your regular aperture ring as far as it will go--the preset ring won't let it go any farther as you already set it at f8.
This is a somewhat primitive way of allowing open aperture focusing without building this feature into the camera, so I would guess that your lens was built in the 1960's. Starting in the 1970's, perhaps a bit earlier, camera manufacturers began building open aperture focusing and even open aperture metering into the SLR cameras they produced.
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