Edited from Sigma Japan’s announcement:
Sigma’s lenses for Sony mount may have a potential aperture operation problem when used with the Sony α33 and α55 Interchangeable Lens digital cameras.
To overcome this issue, we will be offering, free of charge, a modification service to our customers who have purchased a Sony α33 and α55 and own Sigma lenses for Sony mount. This phenomenon will only occur with Sony α33 and α55 cameras. Future production of Sigma lenses will be fully compatible with these cameras.
We deeply apologize for any inconvenience caused to our customers.
When shooting with a Sony α33 and α55 cameras, the aperture may not work properly and a “camera error” message will be displayed on the camera.
Lenses requiring the modification
All current Sigma’s lenses for Sony mount.
For lenses discontinued several years ago, a modification may not be available. For further details, please contact your nearest authorized Sigma Service Station.
Support for this issue
We will be offering a modification service for our current range of lenses free of charge. Please contact your nearest authorized Sigma Service Station.
Mark for compatible lenses
Future production of Sigma lenses will be compatible with these cameras. The above sticker will be put on the product box of compatible lenses.
For further information, please contact your nearest authorized Sigma Service Station.
Depending on whether the aperture problem is entirely mechanical (the coupling) or also involves electronics, it would be fair to assume that problems with the A33/A55 may not be restricted to Sigma independent lenses, but may also apply to other makes, especially older lenses. Brands made by Sigma such as Quantaray are almost certain to be affected. We await Sony’s statement on compatibility with older lenses, including Minolta. Please note that the Alpha adaptor for the NEX E-mount provides normal aperture operation with Sigma lenses; how the A33/A55 mount differs we have yet to see.