All types of lens available in the market feature a point where if we move closer to the object of the photo, the lens cannot focus (blurred). Commonly, this point is called Minimum Focusing Distance (MFD). It is indicated in length (for example 0, 5 m) measured from the distance of sensor in camera to the object of the photo.
If a lens like one in the photo above has an MFD of 0, 45 meter (45 cm) so the Minimum Focusing Distance of the object to the photo sensor is 45 cm if you want the image to come out sharp. When you get closer to the object more than this the image will become blurred. The information of its MFD number is usually printed on the lens itself (as shown in the image above). If you cannot find it on the lens, you might find its specifications in your camera manual book or in lens catalogue.
The information about MFD is not commonly required by general users but if you like macro photography (close up), the number of MFD in a lens becomes so important. Because a macro lens is indeed designed firstly for the need of macro photographers so approximately the MDF of macro lens can reach 16 cm. and because the distance is measured from the light sensor position to the object, it seems like touching the tip of the lens to the photo object and the macro lens can still take the proper focus. The MFD for SLR lens (non Macro) is generally about 30 cm or more.
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