LENSES

Lenses are classified in groups based on their focal lengths and other properties:

16 - 35 MM (WIDE-ANGLE LENSES). Rarely used in medical photography, these are best for landscape and architectural photography. They make landscapes look more expansive and buildings more imposing. They tend to be extremely sharp lenses that have excellent contrast.

50 - 58 MM ("NORMAL" LENSES). These are used for most routine work, including gross specimen photography. It is rarely necessary to use anything other than a normal lens for our purposes except when shooting close-ups so that the lens shadows the subject or if the lens does not allow even illumnation of the specimen. In this case you need:

80 - 135 MM (MEDIUM TELEPHOTO LENSES). These are used for high-magnification macro-photography to increase working distance, and for "over the shoulder" intraoperative photography. For instance, you can be twice as far away from the subject with a 100 mm focal length telephoto than with a 50 mm normal lens and still get the same image size on film.

200 - 2000 MM (LONG TELEPHOTO LENSES). These are usually not used in medical photography but are indispensable in sports, nature, and journalistic photography.

MACRO LENSES. These lenses have an extra long focusing extension to allow you to focus on very close objects. They are generally available in the "normal" focal length and the medium telephoto ranges. For instance, Nikon makes two excellent macros, a 55 mm and a 105 mm. Since they are aimed at the technical market, macro lenses tend to have excellent optics, are very durable, and are several times more expensive than normal lenses of corresponding focal lengths. Most macros in the normal lens category allow you to focus down to objects close enough to give you a "3:1" or "2:1" ratio; that is, the image size is one-third or one-half, respectively, the size of the subject. Most macro lenses can be used with an inexpensive extension ring, which allows focusing down to 1:1 or "life size," i.e., the image size is the same as the subject size (Sigma makes a very nice, not-too-expensive macro lens that focuses down to 1:1 without an extension ring). This allows you to take some breathtaking shots of otherwise unimpressive subjects, such as pituitary adenomas. You can even make a corpus luteum look spectacular.

VARIABLE FOCAL LENGTH (ZOOM LENSES). These are very convenient for general photography, since you don’t have to move the camera so much. I am still waiting for someone to come up with an affordable zoom lens that is macro at all focal lengths and can focus on close objects. Many of the lenses advertised as "macro-zooms" are really just zoom lenses that allow close-up photography only at a fixed focal length. When in "zoom" mode, such lenses are not macro. Other zooms supposedly have "continuous close focusing" throughout their range of focal length, but the specs I have seen on these show that they all have a minimal focusing distance that is too long for practical use on a copy stand. My advice is too stay away from zooms unless you are really up on the capabilities of the individual models and know exactly what you need.

BELLOWS. This is not a lens at all but simply a shade that extends the lens away from the body of the camera. This allows you to take true photomacrographs, producing an image size up to three times that of the subject. For instance, when shooting a 105 mm lens on a bellows at full extension, the Lincoln Memorial on the reverse side of a U.S. penny fills a 35mm frame. The only problem with the bellows is that light intensity fall-off (as per the inverse square law) at maximum extension requires you increase the exposure accordingly. Also you have to be extremely careful about camera motion, which is magnified correspondingly.

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