Who uses 7-spot focus?

Started Dec 8, 2003 | Discussions thread
Victor Engel Forum Pro • Posts: 17,766
Exchanged Lens Today -- New Results (IMGs)

Victor Engel wrote:

I just did an experiment to see if there was some variability among
the various AF spots. The results are posted at

The above is my test using my original lens. I exchanged it for another one at the place where I purchased it. I ran another test almost identical to the first test. The results are shown here:


Differences in procedure:

In my first test, the toothpick holder was vertical. The camera was looking down slightly at it, so the holder itself was not parallel to the plane of focus. So I propped up the toothpick holder with one of the toothpicks and then set the camera on a tripod at a height that made the holder parallel with the plane of focus.

The other thing I did was to take two auto shots at each focus point.

One other change -- When focusing in non-auto mode, instead of turning the focus ring until the light lit up and then shooting, I focused until the light lit up, then backed away until it shut off, then back again slower until it came back on. I did this mainly to take care of any reaction time artifact. I expect this change of procedure should show a bigger difference between the left two columns.

Interestingly, the bottom focus point seems to be nearly dead on. The rest are all off a bit but better than the previous lens. I'm curious why there would be so much difference between two lenses that should have been identical. Any explanation?

 Victor Engel's gear list:Victor Engel's gear list
Canon EOS 5D Canon EOS 5D Mark II Canon EOS 600D Canon EOS 5DS Canon EF 50mm f/1.8 II +12 more
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