50mm and focus issues

During the summer I bought a Sigma 50mm/1.4. While initially I reported that it didn’t have any focusing issues I was slightly mistaken.

It’s true that the 50mm at 1.4 has an extremely shallow DOF and thus most focusing errors will be user errors but there some cases in which the fact that the camera was front focusing became very clear. So I finally took some time earlier this week to set up a tripod and the focus test chart from Jeffrey Friedl (I used the 15% version) and took some test shots while changing the micro adjustment. And writing down which steps I took.

The setup shot

First, let’s look at the result with no adjustment. The images link to full-size pictures for pixel peeping. And warning, they linked images are about 10MB each…

100% crop before micro adjustment

Here you can clearly see that it front focuses a bit. Not too badly, but just a bit. After five different shots with varying micro adjustments I finally settled on +13 which to me is quite good.

100% crop of test after micro adjustment

Of course, I immediately tested the changed setting by shooting a couple of snaps of our dogs that were hanging around. Focusing on Topi’s eye, the image was dead on as you can see:

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