[mic2908]

Imaging-resource hatte wohl Probleme mit dem Sigma 70/2.8 Makro,

The problem is one we encountered in our own lab testing of the Sony Alpha SLT-series cameras, in concert with the Sigma 70mm f/2.8 DG Macro lens, and appears to relate to a miscommunication between camera body and lens. (In our case, the same lens worked correctly on a traditional Sony DSLR body.). Sigma states that the lens aperture may not work properly, and possibly result in a "camera error" message being displayed on the SLT-series body. In our lab, we occasionally found that upon completion of an exposure, the 70mm lens' aperture would remain stopped down. On the subsequent shot, the lens would then incorrectly stop down even further from its previous position, resulting in an underexposed image. Pressing the Depth-of-Field Preview button a few times would generally clear the issue, perhaps providing a workaround for photographers occasionally wanting to use an older Sigma lens with an SLT-series camera, although there's obviously no guarantee that this behavior wasn't specific to our combination of lens and body.

http://www.imaging-resource.com/NEWS/1284151354.html