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For those who don't know, depending on your camera body, the distance to the focus point (subject Distance) may be recorded in the image EXIF data.
I have often wondered if this distance is accurate? Is this an approximation? Is the value impacted by using a FF lens on a cropped or FF body?
Hope somebody knows the answers?
Tony
I don't know how accurate the information is but it's based on the lens so I doubt the crop factor applies. Only the more modern lenses relay this info. It's used for relaying setup info to the flash.
The EXIF data has two relevant fields: focus distance upper and focus distance lower. Neither seem to correspond to the measured distance of a shot, nor does the average of them, nor do they seem to define the DoF of the shot. YMMV.
The focusing mechanism in lenses incorporates a rotary encoder which provides the distance information to the body for use with the ETTL system. It is not what could be called a precision measuring tool. If you want to see what the resolution is, try mounting your flash (ETTL mode) in the horizontal position. As you focus at various distance observe the distance information displayed on your flash. The distance information is not displayed when the flash is tilted up for bouncing as the camera has no means of knowing the distance the light must travel.