Minimum focusing distance variations from lens to lens

What determines the minimum focus distance from lens to lens.  I have noticed differences and haven't been able to put together a pattern on why some are able to get much closer to an object. Is it the number of elements inside or the length of the lens that has the biggest impact on distance? 

G'day Chase

The lens barrel - not the optics - determines the closeness that you might be able to go. The helicoil construction that is the focus ring allows the body of the lens [yes the optics] to travel away from the sensor / film, thus causing the focus point to alter from infinity to something closer than infinity

Most general-purpose lenses extend just enough to allow you to focus to somewhere in the 1-metre to 1/2-metre sort of range ~ obviously big 300mm plus lenses don't come this close, but 'regular' lenses will do so

For you to focus closer than the 'regular' close-focus distance with an SLR, you need to insert a hollow tube [extension tube] between the camera and the lens, therefore forcing the optics yet further away from the sensor/film

Another way of forcing the focus point closer than the original minimum focus is via the use of an accessory lens, called a 'close-up' lens. This attaches to the filter thread at the front of the camera lens [any lens whatsoever so long as it has a filter thread] and it acts like a magnifying glass and forces the focus to get closer & closer - depending upon the optical strength of the close-up lens.

Extension tubes cost from $50 to $200 depending on their electronics; with high quality closeup lenses costing from $50 to $100 depending upon the diameter of the glass

Hope this helps ~ have a sqwiz at my Flickr pics for more details if you wish
Phil from the great land Downunder
www.flickr.com/photos/ozzie_traveller/sets/

There is a so called standard construction to each focal length
that will determine the minimum focal distance. Given special
applications, the MFD many be achieve through the macro spe-
cific element movements ie the circle of projection will be en-
larged toward the body.

This was more noticeable with the old Nikkor 55 macro where
both ends of the barrel were extended when getting closer to
the MFD.