Jeff Keller wrote:
> The Sigma has three small screws. The aperture tab appears to have been
> mounted in a 120 counter clockwise position. The ring does have a couple
> slots. The larger slot where the fricken max aperture tab should have been
> is at about the 1:00 o'clock position. It has another slot at about the 9:00
> o'clock position where an aperture stop down tab would normally be but where
> the fricken non-moving max aperture tab is!
>
> http://www.olympus-photography.com/Catadioptic-Mount/index.htm
>
Here is a pic of a correctly assembled one. I didn't buy this new, but
it was in LN condition and works correctly on my OMs
<http://www.moosemystic.net/Gallery/tech/SIGMA600mount.jpg>.
> The Sigma mount does look like it used parts from a conventional lens having
> a stop down lever. The size of the mount seems to perfectly match the rest
> of the lens.
Yep, mine above also looks like they used their generic lens as on other
lenses with adjustable apertures, but with no max fstop tab and a fixed
stop-down tab.
> Both Tamron and my Sigma have 30.5mm filters.
>
My above Sigma uses 22.5 mm filters.
> My Sigma has a 95mm lens cap whose outer diameter is a tiny bit smaller than
> the outer diameter of the lens barrel. The cap might interfere with the
> reversed hood if it were larger.
>
Mine has cap and hood designed as you describe BUT the filter size is 86
mm, so both parts are smaller. Also, the body finish is a shiny black,
while yours appears to be matte black.
So it appears there are at least two different versions of this lens. I
would assume that mine (both mounts), with smaller slip-in filter and
front filter threads, cap and hood, is the later version. I doubt they
would move from a smaller to a larger lens size.
Darin wrote:
> Ok, now I know this isn't the original mount, although it is from another
> Sigma lens. Sorry I don't have a digital camera to show you what this
> one looks like, but I found a photo of a lens on that site with the same
> mount, it's a Sigma zoom 21-35mm f 1:3.5~4.
> <http://img.photobucket.com/albums/v626/cougar101/Sigmamount.jpg>
>
Take a look at my above image. I suspect yours is the original mount. It
is indeed differently set up than on a lens with an adjustable aperture,
but the differences are just what is needed to use it on a lens without
adjustable aperture. Sigma wouldn't go to the trouble of making a
special version of their OM mount just for the one lens.
> After removing the mount from the lens it was very obvious that it has
> been modified. The tab indicated by the red arrow has been removed.
>
As on mine, not needed in this application.
> The DOF preview button has also been disabled, and is now just glued in to
> plug the hole.
>
Again, there is no diaphram for the DOF button to operate, so the button
is superfluous. But they don't want to leave a hole there, so they put
in a dummy button. Mine also has a dummy button there that doesn't move.
It sounds like all yours needs is to have the aperture tab fixed in
place. You should be able to see from my pic where the correct location is.
Let me say again, that mine operates correctly.
Moose
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