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Snerkler

I have the Sony A77 with 16-50mm and I've never thought the lens is as sharp as reviews I'd read. I'm fairly new to photography so just put it down to user error. However, after running some DOF tests it highlighted what I'd always thought so ran some more tests.

I had the camera set up at 50mm and on a tripod using a remote shutter release to eliminate any camera shake or user error. I focussed using the centre focus point on different textured items at different camera to subject distances, each time taking 3 shots at 0 micro adjustment, +3, +5, +8, and +10. Every time the image was not sharp at the focus point using 0 micro adjustment. It was definitely front focussing. I found that the image was sharpest at +8 or +10 depending on camera to suject distance. At smaller camera to subject distances the more pronounced the issue, as you'd probably expect due to DOF.

Fine I thought, I'll just leave it on +8. However, after using the camera for general use I kept getting very blurred images at certain times and realised that it was when I was using any other focus point other than the central one. Further testing showed that at +8 all other focus points other than the central are massively back focussing, and that all other focus points work best at 0 micro adjustment.

On further shots I noticed that at 16mm focal length using the centre focus point set at +8 Micro adjustment the images were again very blurred and it worked best at 0 micro adjustment. I tried different focal lengths and found that as the focal length increases the centre focus point front focusses more and more.

So to summarise, at 16mm all focus points are acceptable at 0 micro adjustment. As you increase to 35mm the centre focus point front focusses and needs adjusting to +5. All other focus points are acceptable at 0 (note not quite pin sharp being picky). At 50mm the centre focus point needs adjusting to +8 or +10, all other focus points are acceptable at 0.

So why does the centre focus point front focus with increasing focal length, and why is it not universal across all focus points? Is this a known issue, or is this an isolated problem? Again, this was done using a tripod and remote shutter and I can reprouce the same issue EVERY time. It is actually the same hand held, but obviously you could argue that there's user errors creeping in hence doing it on the tripod.

I did also test it using charts, which showed front focus too, but tbh I don't find these tell the whole story of every day shooting hence me testing on real world subjects.

I have contacted Sony directly, but in the meantime any feedback appreciated.

Edit: I forgot to mention that when using the centre focus point at 0 micro adjustment the focus peaking shows that the correct area is in focus, but when the picture is taken it clearly isn't.

Here's an example (100% crops)

Centre focus at 0 micro adjustment

http://www.flickr.com/photos/99443690@N04/13174960595/in/set-72157642400479024/

Centre focus at +8 Micro Adjustment.

http://www.flickr.com/photos/99443690@N04/13175227304/in/set-72157642400479024/

Bieomax

I would probably say to send it into sony to service it as it sounds abit ropey.

One question I do have is when on the tripod did you turn off Steadyshot ? as alot of people suggest turning off the Steadyshot as then tripoded so you don't run the risk of the camera trying to compensate for something which isn't there.

my only other thought is around the mirror, does that look clean and undinted? as the mirror is used for the autofocus and are very very easy to dint/mark since its a thin film tensioned on a frame (akin to clinic film) I marked mine on the A57 with a blowerbrush in the end I just took it out and use the camera in manual focus using the focus magnification to get focus spot on. but then most of my photography I don't overly need autofocus.

If the mirror is damaged they cost about £70ish from sonys uk parts provider www.4sony.co.uk (search for - Sony Mirror POI ) and fitting is easy to do.

Mark.

:::edited original as forum didn'ted allow me to post an abreiviated version of SteadyShot and changed it to stars:::

Snerkler

Thanks for your reply. It is a very weird one indeed. I ran more tests this morning using the chart test to be more 'scientific' and again got the same results. It showed a definite front focus, and looked better at +8 and +10. However, as I mentioned in the first post if I correct this then shooting with larger camera to subject distances (over 3m or so) or using the lens at 16mm it causes huge back focus, in that it focuses around 2ft behind the focus point.

I ran the same tests with my Sony 50mm F1.8 again as well and this does not have the same issue. This would make me believe that it's either the lens, or the way my camera handles zoom lenses.

Steady shot does not appear to make any difference and looks the same on or off.

I have contacted sony and they have asked to see the test shots. I'll update as I hear more from them.

This is the chart test with 0 micro adjustment. Camera to subject distance is about 40cm to enable as muh of the chart as possible to fill the frame. The chart was at 45 degrees to the camera, measured with a set square and not just by eye.

http://www.flickr.com/photos/99443690@N04/13213763425/

This is the cahrt test with +10 micro adjustment

http://www.flickr.com/photos/99443690@N04/13214080564/in/photostream/

+10 may be one step too much, although ou should have a touch more focus to the rear anyway.