AN INTRODUCTION TO PHOTOGRAPHY IN GENERAL...

AND GROSS SPECIMEN PHOTOGRAPHY IN PARTICULAR

A Guide for Residents Who Have Had This Unwelcome Chore Dumped Upon Them

Ed Uthman, MD

Diplomate, American Board of Pathology

18 Aug 1996

At its birth about 1824, photography as practiced by its first devotee, Joseph Nicephore Niepce, was a messy, all- consuming pursuit that made use of such substances as bitumen of Judaea, lavender oil, and pewter. Today, chemical, mechanical, and electronic technology has made photography a neat, transparent, facile technique which we may easily apply to another messy, all-consuming pursuit: gross anatomic pathology. Despite the amount of automation available in photography, it is important to grasp a few general principles, so that we may use to our advantage a few powerful controls we have over the photographic environment.

The main considerations in gross photography are exposure, focus, image size, composition, color balance, and film selection.

I. EXPOSURE

This is essentially the problem of balancing the amount of light coming through the lens with the sensitivity of the film. We seek the ideal exposure and eschew the underexposure (slide too dark) or overexposure (slide too light). The determinants of exposure are:

II. FOCUS

There are two things to consider here, methods of focusing and depth of field.

III. IMAGE SIZE

The size of the image in the camera depends on 1) the size of the subject (of course), 2) the distance of the subject from the camera, and 3) the focal length of the lens. The focal length is the distance from the lens to the image when the lens is focused on infinity. The effects of lens focal length are as follows:

The greater the focal length,

Depth of field (see section II.B, above) is independent of focal length in the world of close-up photography [this is not true in landscape photography, where lenses with shorter focal lengths have greater depths of field].

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

IV. COMPOSITION

If you consider yourself more of a technical type than an artiste, you are probably intimidated by this aspect of photography. Although Ernst Haases and Edward Steichens are probably born and not made, much technique of composition can be easily learned by the average eye. In gross photography, first step is good specimen preparation. This is what separates the excellent from the mediocre; the inspired pathologist from the drudge; art from mere visual documentation. After you get comfortable with the camera, you should spend almost all your time preparing the specimen, with the actual photography being a brief anticlimax. Here are some tips I find useful:

V. COLOR BALANCE

We perceive a sheet of paper illuminated by an incandescent bulb to be just as white as if it were illuminated by direct sunlight. This goes along with our concept that "white" light is composed of light of all colors. This is true to an extent, but various "white" light sources produce their component colors in varying proportions. For instance, the surface of the sun has a temperature of about 6000 Kelvins and has much more blue light in it than the radiating surface of a tungsten filament glowing at 3200 Kelvins, which has more red light. This relation between temperature of a glowing object and its color is well known to most people (although not by its scientific name - Wien's First Law), since we are taught from the fifth grade that a blue flame is hotter than a red one.

Although the neurological visual processing system behind our eyes compensates for this variability, the film in a camera cannot. The solution is to make film where sensitivity to the colors of the spectrum is specifically balanced for the color distribution of the light source. When shooting in daylight or with an electronic flash, we need to use "daylight" film. Alternatively, when using incandescent lights (such as the floods on the copy stand), we need to use "tungsten" film. This is not some theoretical consideration. If you try to use daylight film with the floodlights you will get an unacceptably orange picture; conversely, shooting tungsten film with a flash will produce a picture that looks like it was painted by Picasso during his "blue" period.

VI. FILM SELECTION

You will select film based on your need for good resolution, your budget, the necessity of rapid processing turnaround time, and the format in which your photographic work is to be presented.

EXAMPLES

For some examples of specimen photographs made using these techniques, check out my Pathology Images Web page.

ACKNOWLEDGEMENTS

Dr. Donald McGavin, Professor of Pathobiology, Univ. of Tennessee College of Veterinary Medicine, generously provided many fine suggestions from detailed review of the first version of this paper, and I have incorporated most of them into the current version.

Lisbeth Kuehn provided some helpful information concerning depth of field, which I was previously unaware of.

I also wish to posthumously thank my father, G. O. Uthman, who taught me, among many other things, the basics of photography.

All opinions given here are ultimately mine, as are any errors.

IMPORTANT

Please send any constructive comments about this paper to Ed Uthman . I am especially interested in correcting any errors that may have crept in.

COPYRIGHT NOTICE

Copyright (c) 1995, Edward O. Uthman. This document may be freely distributed. It may be reformatted for purposes of compatibility. It may be freely used for personal and educational purposes, but it may not be used for commercial purposes without prior written consent of the author. It may be included in toto or in part as components of other documents with proper attribution.

DISCLAIMER

While I have made every reasonable attempt to include only accurate information, it is possible that some of the information is wrong and may result in inadequate photos. Photography is an empirical technique, so experiment liberally with test rolls before "shooting for keeps."

Version 2.04, 5 Jan 1999