Hi Sylvain,
I don't own that lens, so just a few general comments.
I had a look at your samples. I think they resolve, at least in the centre, down to pixel level. Look in your 2bis file, you can see nuts and bolts holding the overhead live wires together. Sample seems to have focussed in front of the main subject, but if you look at the curbstones, some of them show a lot of detail.
Considering the exposure shifts - could you share more detail? Does it get brighter or darker when stopping down. If it gets brighter, you might experience the aperture closing to slow <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/ohmy.gif' class='bbc_emoticon' alt='
' /> To check, I would mount the camera on a tripod and set up a nice bokeh test picture. If you stop down the diameter of the unshare images should shrink by a factor of 2 every two stops. Also the effect of a slow aperture should be less significant in low light levels when exposing several seconds.
Considering the 1/800s. I am not surprised. The old rule of 1/f on 35mm with f being the focal length is from the time when nobody was using a 12MP digital sensor. When looking at a 12MP image at pixel level you are asking a lot. Keep in mind, when I got into photography, everything longer than 200mm was considered a tripod only affair. As suggested before, you might want to test the in body IS, to see whether that buys you a stop.
Enjoy Scotland. I used to live there. With a bit of luck with the weather, it is a magnificent place. I think the Western Isles are the best part.
I don't own that lens, so just a few general comments.
I had a look at your samples. I think they resolve, at least in the centre, down to pixel level. Look in your 2bis file, you can see nuts and bolts holding the overhead live wires together. Sample seems to have focussed in front of the main subject, but if you look at the curbstones, some of them show a lot of detail.
Considering the exposure shifts - could you share more detail? Does it get brighter or darker when stopping down. If it gets brighter, you might experience the aperture closing to slow <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/ohmy.gif' class='bbc_emoticon' alt='
' /> To check, I would mount the camera on a tripod and set up a nice bokeh test picture. If you stop down the diameter of the unshare images should shrink by a factor of 2 every two stops. Also the effect of a slow aperture should be less significant in low light levels when exposing several seconds.Considering the 1/800s. I am not surprised. The old rule of 1/f on 35mm with f being the focal length is from the time when nobody was using a 12MP digital sensor. When looking at a 12MP image at pixel level you are asking a lot. Keep in mind, when I got into photography, everything longer than 200mm was considered a tripod only affair. As suggested before, you might want to test the in body IS, to see whether that buys you a stop.
Enjoy Scotland. I used to live there. With a bit of luck with the weather, it is a magnificent place. I think the Western Isles are the best part.
enjoy