Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It only takes a minute to sign up.
Sign up to join this community
If I know the focal length of a lens, how can I know the minimum focus distance? I know there is mark in the lens, but if I don't have the lens how can I know the MFD?
I have checked several webpage, but I am still wondering whether there's a formula?
It depends entirely on how the lens was designed, there is no general formula or way of determining the minimum focus distance. Lenses of the same focal length can have completely different minimum focus distances depending on which factors the lens designer chose to optimise.
There is no direct relation between focal length and minimum focal distance.
Usually a long focal length means a long minimum focal distance, but that is just because a lens built that way also has other characteristics that are preferable, like having a reasonable focus range.
If you add extension tubes between the lens and the camera, the minimum focal distance will be shorter. That's because you change the characteristics of the lens. With enough extension tubes you can even get a negative minimum working distance (the distance between the front of the lens and the subject), i.e. it can focus behind the front lens element. That shows that you could easily build a lens with any focal length and a very short minimum focal distance, but it would also have a very short focus range.
