The minimum focus distance is the closest distance from the focal plane, the sensor, to the subject at which the lens is able achieve focus. If you get closer than the minimum focus distance the lens will NOT be able to focus on the subject. This typically happens when you try to take close up pictures, for example of flowers, insects or jewelry.
The minimum focus distance is lens dependent and the value can be found, usually specified in feet and meters, via the manufacturer specifications for the lens of interest. For example the Canon 100mm F/2.8 IS macro lens has a minimum focus distance of 0.99ft or 0.3m.
The minimum focus distance is measured from the focal plane, the sensor (NOT the front of the lens), to the subject. The sensor position in your camera is typically marked on the outside of the camera body with a line through a circle symbol, which is the starting point of the measurement.
Some lenses have switches to limit the minimum focus distance so the the camera cannot focus on objects close to the camera. For example, if you wanted to take a portrait of someone through tall grass. In this case you would not want the camera to be able to focus on the close objects, the grass, just on the subject you are trying to take the portrait of.
In our next lesson we will discuss “plane of focus” which is related to a previously discussed topic “Depth of Field“.
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