Jeffrey’s Autofocus Test Chart

Jeffrey’s Autofocus Test Chart

introduction from his website...lots of information about back and forward focusing! Lisa

If you suspect that your modern SLR or SLR lens has autofocus problems, you can use a chart like the one offered on this page to perform some tests.

The basic premise of a chart like this is that when photographed at an angle, the paper slices through the plane of focus. Depending on the situation, that plane can be very thick, encompassing the whole chart (leaving the whole chart in focus), or, more usefully, it can be very thin, leaving only the areas of the chart that intersect with that thin region in focus.

The illustration below shows proper autofocus and the result one might expect from it, where the region of what is actually in focus is more or less centered on the focus target. It also has views for the problems ofback focus and front focus, where for some reason, the lens actually focuses on a region either behind or in front of the focus point (resulting in the in-focus area on the chart to be above or below the focus target). Mouseover the buttons under the chart to see those views.