Checking out lens focusing (A technical post)

Something I have been meaning to do for some time is to check the focusing of my lenses – my camera has a focus ‘micro adjustment’ feature. I had previously done this for a 50mm lens I bought last year, but never go around to checking my other lenses. Below I show the results for one of the lenses, an old (1990’s film era) 100mm macro lens:

This first image shows the lens set at f2.8 with no adjustment (all these images are at 1:1 pixel size):

f2.8 no adjustmentYou can see the softness of this image. Compare it to the ‘+14’ adjustment:

f2.8 adjustment +14Quite a distinct difference! But at f8, the same adjustment looks like this:

f8 adjustmenr +14Not quite as sharp, but better than no adjustment. For this aperture, I found that an adjustment of +8 was best as can be seen below:

f8 adjustment +8As this lens will mostly be used stopped-down, I have used +8 at the setting.

To test, I set the camera up on a sturdy tripod, used mirror lockup and a 2-second delay to minimise camera shake. I took a series of photographs at different adjustments and at 2 aperture settings for each lens. For the other lenses I have, the settings I have used after testing are:

EF 50mm f1.4 = +14

EFS 15-85mm f5.6 = +8

An old film era budget EF 75-300 f4.5-5.6 = +16