Joy wrote:
: There are 2 dials for the apertures...the one
: closest to the camera also has the buttons to remove the lens...is that
: usable? or are those aperture numbers just for reference?
The one closest to the camera is not a dial - it is the lens mount and the
apertures encraved on it are the depth of field (DOF) scale. DOF is the area
in which everything appears to be sharp. This scale is one of the three
methods that can be used to judge the DOF you get with a certain aperture
setting for a certain distance. It also depends on the focal length, so
every lens has a different scale. The other two methods are using the DOF
preview button (also on the lens mount, on the right hand side) that closes
the aperture to the preset value, or using a DOF table for the given focal
length. The scale on the lens mount is used by first setting the aperture on
the aperture dial (the real one, on the front), and focusing. If the
aperture you selected is one the apertures on the DOF scale (4, 8, 16 on a
50mm lens) you can easily read the low and high DOF distances from the
distance values engraved on the focusing ring.
The scale can also be used for two other purposes. One commonly used is the
hyperfocal setting. You choose a small aperture (for instance F16) and
allign the infinity marker to this aperture value. This gives you maximum
DOF. This can be used with standard lenses but is specially effective with
wide angle lenses; everything from very close to the camera to infinity
becomes sharp. The hyperfocal setting is also known as the snapshot setting
because you don't have to focus anymore, allowing very fast reactions. Ideal
for people with the Lomographic Syndrome.
The other purpose is for using Infra Red film. This film gives a focal shift
and the ring contains a small red line that indicates the focus correction
you have to apply with this ring.
Hans
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