These are sample shots hoping to shed some light on the way a known and unremovable blemish in (rather than ON) an APS-C CCD sensor influences real life shooting. The first series (from my bedroom window, it's a family trait, but looking out on Tenbury Wells rooftops not a garden in Wokingham) has the blemish in the sky, and way the effect changes from f/1.8 down to f/22 is clear. These files are quite small, severely downsized from the originals, but are a very fair representation of the problem.

The next series are a bit downsized, but not much, and start at f/2.8 down to f/22. The intention was to do a more real-life demonstration with the 'spot' not in the sky... They were hand held, so the problem spot isn't always in quite the same place, but it's never far off the Ludlow castle masonry. I know where to look, and I can see it clearly at f/22 and not quite so obviously at f/16 and I expect you will be able to also. Those last two shots aren't downsized at all, it should be interesting to look at them at 'original' and 'large'. I'll leave it up to other eagle eyes to look for it at f/11 and wider - and then decide whether it would be a problem for the sort of shots you take, even if you can.

The shots after that are a selection of shots I've taken with my D2X, and particularly with a combo of the D2X/TC-16A MF to AF teleconverter and my Tamron SP Adaptall 300/2.8, which is (in APS-C 'crop factor' terms) an AF 720mm f/4.5 lens - but only for Nikon DSLRs, on the D2 series.

The EXIF is accurate, those with Focal length 500mm are with the 300/2.8 + TC-16A combo.