Help identifying button on lens

Gadgie

I have two Olympus Zuiko lenses. One of the lenses has a button that stops the lens diaphragm down to the taking aperture, while the other does not - the aperture is fixed in whatever position has been selected on the ring at all times. It looks like this lens never had such a button, as the place where the button should be is sealed as part of the metal (see first attached image).

On the underside of the lens with no button, the little metal sliding switch remains fixed in place, while on the lens with the button, this switch moves depending on whether the button is pressed or not (see second attached image - lens without button is on the right).

As you can probably tell from the terms I'm using, I'm not a photographer and know little about cameras and lenses. I was wondering what the correct terms are for these buttons and switches, and why the lenses would differ in this way.

Thanks for any help on this matter!

DaireQuinlan

The second one looks as though someone actually intentionally removed the button, and put a blank in its place, to ensure that it's always in a 'pressed' state and the lens always stops down to whatever's set on the aperture ring.

Most modern SLR lenses will stay fully open when the aperture ring is turned, and there's normally some mechanism in the camera body to close them down when the shutter button is pressed. In addition there's normally some method either on the camera body or (in this case) on the lens itself to close them down manually, to check DOF for example, or to perform stopped down metering on older bodies.

The little metal sliding switch probably communicates the set value of the aperture to the camera body for metering purposes.

I'm just supposing here, I'm not familiar with the OM mount.

If I was to venture a suggestion, I'd say the second lens without the button has been intentionally crippled to always stop down to the chosen aperture for some reason, maybe to mount it on some adapter for use on a different camera or something, but I could be completely off-base here.

magicbastarder

yep, that's the depth of field preview button.

Gadgie

Thanks for the info. I suspect the lens without the button was being used on some industrial equipment, so it was probably modified for that reason.

cnocbui

These are Olympus OM Zuiko lenses made for their 35mm OM film cameras.

These are purely mechanical and there are no 'switches'. The levers on the lens mount are 1: to indicate to the camera body what aperture has been selected by the aperture ring 2: the aperture stop-down lever which closes the aperture blades to the selected value when the photo is taken.

As mentioned, there is also an aperture stop down button so you could temporarily close the aperture to preview the effect in the viewfinder.

Looks like they might be 28mm f2 ? If so, very nice lenses.

These can still be used to great effect on Canon bodies and on M4/3 cameras via an adapter.

Gadgie

cnocbui wrote: »

Looks like they might be 28mm f2 ? If so, very nice lenses.

Yeah, they are 28mm F2.

Thanks for the extra info.

zerohamster

This could have been done for use with an adapter on another camera that would otherwise be unable to move the lenses mechanical diaphragm or for video use also as it would make changing the aperture during shooting easier.