Lord knows why I bought it (circa 1980) but the bellows material is still lightproof and the knobs still work, which is, I suppose, about all you want in a bellows.

Next, I tracked down an SRT 101 which had been sitting in a local camera shop since the Reagan Administration. This clunky thing has a mirror lock, self-timer, DOF preview, a bright viewfinder and it's massively cheap, which is, I suppose, about all you can want in an SLR for macro work.

However.......digging further into my collection I found the only Minolta lens I own is a 45mm Rokkor, which seems to focus only when the front element is actually trying to nudge the tiny little thing I want to photograph.

So my question is: got camera, got bellows, got tripod, no got lens. What should I stick on the front of this contraption so it doesn't crush little bugs and flowers: 55, 50, 100? What if I whip the little 45 on backwards?

Field macros are usually done using a long lens between 80mm and 135mm, occasionally a little longer at 180mm or 200mm, or a little shorter at 50mm. I have done them using lenses as short as 24mm and 18mm, but that is very special work, and requires great care in setting it up very, very close using a very short extension tube. The reason for the longer lenses? They allow farther standoff from the subject for the same level of magnification.

For insects, fruit and leaves, I suggest starting with an 80mm to 90mm lens and a set of extension tubes of at least two lengths, about 12mm and 25mm, if you system has them available. You can stack extension tubes, but usually no more than two, sometimes three. How many depends on the tubes, who makes them and the size/weight of the lens that will be used also.

The Canon EOS system has two tubes (12mm and 25mm). The Nikon AF system has an extension tube also. Kenko makes tubes for Canon, Nikon, Pentax and Minolta AF systems. Tubes were made for older, manual focus systems by the original OEM, and Vivitar still makes sets for them (the Vivitar is a sturdy one with three tubes: 12mm, 21mm and 36mm).

You will also need a sturdy tripod. At the high magnification levels of macro work, it becomes very difficult to hand hold without camera shake blurring the image and depth of field becomes very shallow making accurate focusing critical.

The next paragraphs describe how macros are measured and the several methods for doing them.

Magnification is the real measure of macro work. It is the ratio of the subject size _on_film_ (not on the print) to actual subject size. A 1:1 or life-size will be life-size on the film. A true macro lens (versus close-up or close focus) will let you get at least 1:4 (1/4 life-size) or larger.

There are three standard methods for doing macros:
a. Auxiliary "diopter" lenses that screw onto the front of a lens (sometimes called close-up "filters" but they are not really filters). Most of these are OK but not the best optically, especially the inexpensive ones with only a single lens element. The more expensive two-element ones are much better but as expensive as extension tubes, which are usually still better optically.
b. Extension tubes that go between a lens and the camera body. These move the entire lens focusing range closer. The length of the tube compared to the focal length of the lens determines how much closer you can get and the level of magnification you can achieve. They are better optically than auxiliary diopter lenses as there is no glass in them, especially if used with an excellent prime lens with little or no aberration or distortion. Extremely close work with very high magnification can be had with a bellows extension (even longer than tubes) but they are rarely used outdoors. This is part of the tradeoff with longer focal length to get greater standoff distance. A longer tube is needed to get the same magnification level. A 50mm lens at infinity focus needs a 25mm tube for 1:2 magnification. A 100mm lens will have 1:2 magnification at twice the subject distance, but requires 50mm of extension to achieve it.
c. A true macro lens which is specifically designed and optimized for much closer focusing than a normal one to get at least 1:4 magnification, sometimes 1:2. These are typically more expensive and slower, but they are also usually the best optically, especially the primes (non-zoom). For even higher magnification you can add extension tubes to them just as you would a normal lens.

How much magnification you need depends on subject size and how much you want to fill the film frame with it. For small insects, this could be between 1:2 to 1:1, or half life-size to life-size (a 35mm film frame is about 1" x 1.5"). For larger insects such as a preying mantis or grasshopper, 1:4 to 1:3 magnification would fill the film frame. For flowers and leaves, it depends on the size of the flower blossom and how much of it you want in the frame. A single African violet blossom could require 1:1 whereas a cluster of them requires less, perhaps 1:4. OTOH, an oak leaf or an orange may only need 1:6 magnification.

Think about the size of the objects you want to photograph and compare this to the size of a film frame (35mm: about 1" x 1.5"). This will tell you the magnification levels you need. You can then sort out how much magnification a "macro" lens must provide (by looking at various lens specs), or figure out how much extension tube you need with a normal lens of a particular focal length.

I was going to buy Canon's 50mm f1.4 prime lens for this work, but in doing some research I find that most photographers use macro lenses for the specific things I'm interested in, usually 105mm, or similar. Canon makes a 100mm f2.8 macro (1:1) that sounds like what I need. I have also seen a Vivitar 100mm f3.5 macro (1:2) that does 1:1 with an included adapter for much less money.

You could save some money here by locating a good manual focus 100-mm macro lens, and then buy a manual focus body and dedicate it to macro. You don't need autofocus with macro, anyway.

If you are going to do a lot of 1:4 to 1:1 and higher magnification macro work, especially with 85mm and longer lenses, extension tubes, and/or bellows, then it is a definite consideration.