Close-Up Exposure Guide
A rough guide to exposure increase
for simple lenses extended with tubes or bellows. Not covered by this method
are zoom lenses, retrofocus wide angle, and telephoto lenses. Tele and retrofocus
lenses are not very good close-up lenses and require different calculations.
Some retrofocus lenses in reverse work well for very close work.
For any 35 mm camera image academy
high (.631") in the viewfinder (and on the film), the following heights of objects
will determine the exposure increase for most lens.
Object Height Exposure Increase
2.6"(2-1/2") 1/2 stop
1.3"(1-1/4") 1 stop
.76"(3/4") 1-1/2 stop
.631"(5/8") 2 stops
.38"(3/8") 2-1/2 stops
.29"(1/4") 3 stops
Retrofocus lenses need less exposure
increase. Retrofocus lenses are not the best for very much extension, though
some perform quite well in the reverse mode. There is a lot of information out
there in the still literature about close-ups. Telephoto lenses need more exposure
than calculated, but also are not recommended for close up work. Also avoid
fast lenses for close up work.
A useful tool for exposure calculation
is the single lens reflex camera with a similar lens. If you don't have one,
be sure to get one that will meter exposure in the stopped-down mode with non-automatic
lenses. The camera is useful for getting the feel of close-up work without the
bulk of a movie camera. If you use a still camera for exposure calculations,
make sure that you have a way to get the movie camera out of the shooting position
easily, maybe on a Ubangi to swing it away.
Minolta and others make small probe
attachments to take incident exposure readings in tight places and also a low
light reflected attachment that can be modified to read the brightness on the
ground glass through the viewfinder. This last item takes calibration and remember
the illumination on the ground glass may not be as much as on the film for lenses
with rear elements close to the ground glass. As with any new system, test it
for a while before you trust it in production.
Spot meters and gray cards are very
useful. Make sure that you read from the same camera angle for shiny objects.
Be sure to make the lens extension factor calculations. The chart at the top
can be used.
Zoom lenses will focus closer if
moved out of their mount. The focus will get closer as the lens is zoomed wide.
The exposure compensation is made for the maximum focal length of the lens which
is often negligible. This trick can be useful for "racking" through
small objects at different distances from the camera. Use the zoom to change
image size and focus at the same time. Donít let light leak around the lens
© Copyright 1999-2004 Ron Dexter. All Rights Reserved