Originally posted by enrod666 I am attaching a picture I took with my 18-250 mm lens. You can notice the vignetting problem.
Is it normal that the vignetting does not appear to be symmetrical? Does this point to a decentering problem?
Most of the time, I don't seem to have a vignetting problem with my Tamron 18-250. Sometimes, though, mainly one corner shows the vignetting symptom.
I have checked the lens for decentering and it appears to have pretty much the same sharpness in all four corners.
Could the shake reduction mechanism be the culprit? When a lens vignettes and the sensor is moved out of its centred position, the vignetting should be non-symmetrical.
When I look through the lens (at the front element, at the light coming through the viewfinder) when stopping it down (with optical preview) I notice that one aperture blade is a bit "faster/earlier" than the others and one is a bit "slower/later". The resulting shape doesn't resemble a circle a lot. I didn't notice it from bokeh shots, though. I guess that an uneven aperture cannot cause such a "one corner vignetting" though.
I still have warranty on the lens. Would it make sense to send it in, pointing out the "one corner vignetting" and the odd aperture shapes? My copy seems to a good one (even corner performance), though, and I'm hesitating to have it butchered up by attempts to fix problem that don't really deserve attention.
Last edited by Class A; 12-24-2008 at 01:01 PM.