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Macro Photography
The effort of setting up your tripod is so great that you become tired and fall asleep. When you wake up in the morning, there is a bear
standing 10 feet away. You refocus your 50mm lens to get a picture of the grizzly. As you turn the helical from "infinity" to "10 feet",
notice that the optics are racked out away from the film. The nodal point is a bit farther than 50 millimeters from the film plane. The
lens is casting an image circle somewhat larger than the 24x36mm frame. Some of the light gathered by the lens is therefore being lost
but it isn't significant.
After snapping that photo of the bear, you notice that his fangs are glistening. These aren't going to appear very large in your last shot,
so you move up until you are about 1.5 feet from the bear. That's about as close as the Nikon lens helical will let you focus. The nodal
point is now pretty far from the lens. Extra light is spilling off to the edges of the frame , but still not far enough to require an exposure
correction. The bear's face is 1.5 feet high. You've oriented the camera vertically so that the face fills the 36mm dimension. 36mm is
about 1.5 inches. So that means you are working at "1:12". The subject is 12 times the size of the subject's image on film.
You're losing some light, but also you notice that you don't have too much depth of field. A 50mm lens focussed down to a foot from
the subject only has a depth of field of 1/16th of an inch at f/4. No problem. You haul out a big electronic flash and stop down to f/11.
Now your depth of field is a whopping ... 1/2 inch.
Looking down, you become fascinated by some pattern's in the bear's claws. Each one is about 1.5 inches long. You'd like to fill the
35mm frame's long dimension with a claw, which means that the subject and its image will be the same size. You want to work at "1:1".
But those scumbags at Nikon skimped on the helical. You can't rack your optics out far enough to focus at 1:1. It looks like that pine
needle tip photo is completely out of the question.
Why did Nikon limit your ability to focus close? For starters, at 1:1 your lens would be so far away from the film that it would cast a
huge image circle. The standard 35mm frame would only be a tiny fraction. So only about 1/4 of the light gathered by the lens would
reach the film. A scene that required a lens setting of f/16 at infinity would require a lens setting of about f/8 at 1:1. All this other light
would be bouncing around inside your camera and lens, reducing contrast. Finally, a fixed stack of optical elements can't be designed to
form sharp images at so many different focussed distances.
Close-Up Lenses
Your eyes don't focus so great on really small things either. Do you try to pull your cornea a foot
away from your retina? No. You stick a magnifying glass in front of your cornea. You can do the
same thing for your 50mm lens. Unlike your cornea, it even has convenient threads for attaching a
magnifying glass.
A photo shop could never sell you a "magnifying glass" for $50 so they call these things
"supplementary lenses" or "close-up lenses". Good things about close-up lenses:
● they don't require any exposure corrections
● you can throw a couple in your pocket in case you need them
Bad things about close-up lenses:
● they aren't very high quality though they might be good enough if you stop down to f/16 and if you can find two-element closeup
lenses (e.g., Nikon-brand) instead of the cheapo one-element ones.
● you have to take them on and off constantly if you are taking pictures of things at different distances.
I never use close-up lenses but they are described fairly thoroughly in the Kodak Professional Photoguide.
At right: a model of Sacre Coeur, captured with a Minolta 50mm lens and single-element Minolta-brand close-up lens. The image has
lots of problems but I think I was 11 years old when I took it.
Macro Zoom Lenses
http://www.photo.net/macro/primer (2 of 8)15/11/2004 6:47:08 PM