Was Gifted a Third Party 18mm F3.2 Minolta MC mount lens

[Bill Smith]

So a friend of my mom stops by and drops off two 1970s vintage Sigma Lenses with a Minolta MC mount, the telephoto zoom is fine but the 18mm f3.2 Widerama (their word, not mine) won't open up past F11. So how do I unjam this lens so I can use it?

[Dean Williams]

Bill, some (not all) of these lenses have a small button behind the aperture ring or in a small recess near or on the
back of the lens body.  If it has one, it will stop the lens from opening past the selected preset.
Another thing can be if it has two levers sticking out of the back of the lens, around the rear element, near the mount.  One
of those levers is the stop down preview, and one is an index for metering.  The index one may need to be moved to let
the lens open up.  It normally gets set properly when the lens is mounted on the camera body.

There are a couple of mechanical linkages inside the barrel that operate the aperture, too.  If one of those is stuck,
the lens needs to be disassembled.  Same if the blades have oil or a piece of grit in them.

Sorry, these aren't really solutions.  Just some info.

Dean

[Bill Smith]

Hi Dean,

Having a closer look at the lens, it looks like one of those universal mounts third party lens makers loved to use back in the 1970s, seeing how the aperture open and close I sorta wonder if the mount itself was improperly installed.

[LarryD]

Remove the mount and check? But I don't remember Sigma making a T mount with their name on it.
And they never made a Multi mount. Like the Tamaron lenses. If all else fails F11 is not too bad for a lens that wide....

[Bill Smith]

Remove the mount and check? But I don't remember Sigma making a T mount with their name on it.
And they never made a Multi mount. Like the Tamaron lenses. If all else fails F11 is not too bad for a lens that wide....

This is indeed a T-mount lens from Sigma, my guess early/mid 1970s with the all metal construction. I'm sorta wondering if it has the wrong adapter for the lens. Well it opens up to F8 which isn't too bad.