Thursday, August 30, 2012

Somewhat confused :-(

85mm at f8
Yesterday I was getting quite concerned about the accuracy of focus on my 85mm lens.  I'd taken a few photos in the front yard of cherry blossom and felt that the focus wasn't as accurate as I'd hoped for.  I came inside and tried a few things with a tape measure and "AFS Fine Tune" that seemed to suggest the camera/lens combination was focussing slightly in front of where it should.  I tried autofocus with my 18-200mm and this seemed spot on.  I then tried a manual focus with the 85mm lens and this was spot on.

Using the AFS Fine Tune was quite straightforward, but didn't seem to fix my problem.  Even at the fullest extent of the fine tune my image still seemed to be focussing in the wrong place.  To check out the camera/lens combination seems to require a few days, so that can't happen for a wee while, and it would appear from the brief tests I've done that I should really check my other lenses as at least the 18-200mm is spot on.

Anyway, hoping I'd made a mistake and was imagining the problem, I went into the backyard to take some shots of the kowhai blossom.  The first shot was taken at f8 with the 85mm lens.  Camera and lens mounted on a tripod.  This is pretty sharp, but at f8 I'd expect it to be!  Also the leading flower, pretty well central to the image seems nicely focussed.  Interestingly my attempts at manual focus didn't give as sharp a result as the autofocus attempts.  This was the opposite to last night's ruler experiment shots.  Not pleased with the busy background, I opened up the lens and tried again at f1.4.
85mm f1.4
Using autofocus again on the leading flower but this time it seems acceptably sharp (bearing in mind the lens is wide open and the there was a little breeze).  My attempts at manual focus were not as accurate as the autofocus and I'm beginning to wonder if I'm imagining things.  To get the camera and lens checked will take a few days and cost at least $100.  Is it worth it I have to ask and how much better would the images be if the setup was tuned?  As I said at the start ... somewhat confused :-(

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