Bellows and bellows lenses
Like extension tubes, bellows units come in both manual and automatic
versions, the latter retaining all the automatic exposure functions of
camera and lens when you use a double cable release. Some units have
just one track (or set of tracks) used only to support the bellows and
to set the desired length. More expensive units have an additional set
of tracks (or some similar device) to allow the camera/bellows/lens
assembly to be shifted as a whole for easier focusing at very close
distances.
However, the thickness of a bellows prevents an ordinary lens from being
racked all the way back to its infinity position, the farthest point of
focus is quite near even when the bellows is compressed all the way, and
it is closer still when the bellows is extended. The particular range
depends upon the focal length of the lens. There is, however, a special
optic called a bellow lens which has a much greater focusing range
because it come s in a short mount. That is, the total length of the
mount is much shorter than the focal length of the lens. When the
bellows is compressed all the way, the total thickness of camera,
bellows and mount does not exceed the lens focal length. Therefore, this
kind of lens can be focused from infinity all the way down to fractions
of an inch. (This is true when all components are from the same
manufacturer, but may not be true otherwise.) Furthermore, short mount
bellows lenses are usually macros, which means they are designed to work
best close up. However, any lens on a bellows can get you into the true
macro range, defined as the range where magnifications start at full
life size and get bigger from there. ________________________________________________________________________
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Supplementary close up lenses
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