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Gross Specimen Photography (monthly posting, 34K, v. 2.03)


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Version: 2.03
Last-modified: September 2, 1996
Archive-name: pathology/gross-specimen-photography
Posting-Frequency: monthly (first Wednesday)
URL: http://www.neosoft.com/~uthman
Maintainer: Ed Uthman <uthman@neosoft.com>

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        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 <uthman@neosoft.com>
          Diplomate, American Board of Pathology
                              


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:

A. FILM SPEED, measured as arbitrary standardized units
   ("ISO" or, formerly, "ASA"). ISO and ASA are numerically
   equivalent units. The film speed depends on film
   manufacturing process and type of development used on the
   exposed film. Although films are packaged with a stated
   ISO rating, some may be "pushed" to higher speeds by
   special processing techniques. This should be kept in
   mind before throwing away valuable film you have
   mistakenly underexposed. The faster the film, the less
   the resolution (causing increased "graininess"); also
   colors are more subdued in fast film (such as Kodacolor
   1000) than in "slow" film (such as Kodacolor 25). The
   graininess and subdued colors of very fast films can be
   used for artistic effect but are of no value in technical
   photography. Therefore, we tend to choose slower films
   for our gross lab cameras, so that we may produce
   pictures with the greatest resolution and most accurate
   color rendition. A film faster than ISO 160 should
   probably not be used.
  
B. APERTURE, the setting of the iris diaphragm in the lens,
   determining how much light is allowed through the lens
   into the camera. Aperture measured as "f/ stops" (f/2.8,
   f/4, f/16, etc). The f/ ratio is calculated by dividing
   the focal length of the lens (see below) by the diameter
   of the iris diaphragm opening through which light passes.
   Therefore, the greater the diameter, the more light is
   let in, and the smaller is the f/ ratio. Each f/ stop is
   1.4 (the square root of 2) times the preceding f/ stop.
   Each "stop" multiplies the amount of light by 2X. As an
   example, f/1 lets in twice as much light as f/1.4 and
   four times as much as f/2. The "speed" of the lens is its
   f/ ratio at its widest aperture setting. An f/1.2 lens is
   considered very "fast," while an f/5.6 lens is "slow."
   Generally, fast lenses are more expensive than slow ones
   and in fact do not have as good corner-to-corner
   resolution as slower lenses. Because we generally have
   plenty of light at our disposal in gross photography, we
   opt for excellent resolution over lens speed. Most lenses
   for our purposes are f/2.8 to f/4 at their widest
   aperture settings. We typically choose to "stop down" our
   diaphragms in most cases, because almost all lenses have
   optimal resolution when not used at their maximum
   aperture. The "ideal" f/ stop is generally taken as 2 to
   2-1/2 stops "down" from the maximum aperture. For an
   f/2.8 lens, therefore, the optimal aperture setting would
   between f/5.6 and f/6.7. The other reason to stop down
   from maximum aperture is to improve "depth of field" (see
   "Focus," below). I personally shoot almost all my
   specimen photos at f/8.
  
C. EXPOSURE TIME, or "shutter speed," measured in seconds or
   fractions of seconds (1/30 s, 1/1000 s, etc) represents
   the total time the film is exposed to the focused image.
   It is determined by setting the camera shutter to open
   for a specified length of time.
  
   Effects of various shutter speeds:
  
   1/1000 sec - 1/60 sec: These are OK for hand held camera
   in existing light.
  
   1/60 sec : Always use this with electronic flash, since
   just about all flashes are specifically synchronized for
   this speed. Using a slower speed (e.g., 1/30 sec) will
   also work, but a faster speed (e.g., 1/125 sec) will ruin
   the picture by failing to expose part of the frame. Note:
   Some of the more modern and/or expensive cameras allow
   flash synching at 1/125 second or faster speeds, but make
   sure this is true of your camera before trying it.
  
   1/30 sec - 1/2 sec : We tend to use this range for tripod
   or copy-stand work, including gross photography. This
   range is generally not acceptable for hand-held cameras,
   because most people cannot hold the camera still enough
   for this length of time. By using these slower speeds for
   gross photography, we allow ourselves the luxury of
   smaller apertures (giving us good depth of field and
   maximum resolution from the lens) and slower films
   (giving us maximum film resolution and best color
   rendition).
  
   For example, each of the following exposure parameter set-
   ups give the same exposure. Which would you choose for a
   gross photograph taken on your copy stand, assuming you
   have a camera with an f/4 lens?
  
     A. ASA 50 film; f/4; 1/30 sec
     
     B. ASA 50 film; f/8; 1/8 sec
     
     C. ASA 200 film; f/16; 1/8 sec
     
  I would choose set-up 'B.' Set-up 'A' involves shooting
  at maximum lens aperture, at which lens resolution is not
  the best. Set-up 'C' lets us stop down the aperture for
  good lens resolution but requires us to use faster film
  with poorer resolution than the ASA 50. Therefore, 'B'
  looks like the best compromise.
  
  Even though a good copy stand will keep the camera
  motionless and allow long exposure times, there is a
  theoretical problem, called "reciprocity failure," which
  may interfere with color balance in very long exposures.
  But this is never a problem as long as you don't allow
  the exposure time to exceed 1/2 second, and you'd
  probably not notice it even if you shot a 2-second
  exposure (which may occasionally be necessary when using
  bellows at maximum extension; see below).
  
  How do you determine exposure? There are two ways to do
  this:
  
  1. Most cameras have a built-in light meter that monitors
     the amount of light coming through the lens. This meter
     attempts to optimize the exposure either by averaging
     the total light hitting the film plane (an "averaging
     meter") or using a small sample area (usually the
     center of the field) to measure the amount of light
     focused on that particular spot (a "spot meter"). In an
     "aperture priority" system, the meter then looks at the
     aperture you have set on the lens and automatically
     adjusts the shutter speed to give the desired exposure.
     In an "shutter priority" system, you set the shutter
     speed and the light meter automatically adjusts the
     aperture. These functions are available in what is
     referred to generally as the "auto" mode. In addition,
     most modern cameras have a "program" mode, which
     completely automates exposure determination by choosing
     both the aperture and the shutter speed for you. This
     means all you have to do is compose the picture, focus,
     and push the button.
     
     Program mode has been a boon for photography in
     general, because it allows you to concentrate on
     composition and not have to worry about fiddling with
     aperture rings and shutter speed knobs. There is,
     however, a price to pay, especially in technical
     photography. The main problem is that automatic
     exposure systems (except in high-end cameras) are
     standardized for snapshot type photography, where there
     is no striking difference between background and
     subject illumination. Also, an automatic exposure
     system will attempt to make the subject have a
     "neutral" brightness. In technical photography, we do
     not necessarily want this; we want brain to look light
     and spleen to look dark, just like these respective
     subjects appear to us in real-time. Therefore, I do not
     use the camera's automatic exposure system for routine
     specimen photography.
     
  2. Because of the above considerations, I recommend that
     you take advantage of the rigidly standardized exposure
     environment of the copy stand and virtually always use
     manual exposures. Determine the ideal exposure by
     shooting a roll of film at various settings and then
     stick with this exposure when shooting specimens. You
     can still use the light meter when faced with an
     unstandardized situation, such as having one of your
     four floodlights burn out on Saturday and not being
     able to find a replacement.
     
     Parenthetically, I have found through experience that
     when shooting documents of black printing on white
     paper, you should use an exposure one stop brighter
     than your standard setting for specimens. For instance,
     if you normally shoot specimens at f/8 and 1/8 sec, you
     should choose f/8 and 1/4 sec when shooting a document.
     Never, never let the camera shoot black-on-white
     printed documents on "Auto" or "Program," because the
     camera will think you want the white paper to appear
     neutral and will force a bad underexposure.
     
     Another hint: When forced with shooting pictures on a
     set-up you are unfamiliar with, you may have no idea
     what settings to use. A good solution is to meter on
     the palm of your hand (believe it or not, it makes no
     difference what color you are; the palm of everyone's
     hand looks about the same to a light meter) and note
     what settings the camera's light meter indicates.
     Simply switch over to manual and enter these settings.
     Then you can shoot away and always get at least
     acceptable results.
     
II. FOCUS

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

A. Methods of focusing.
  
  1. Autofocus. Most manufacturers today produce autofocus
     cameras aimed at various markets. The most popular of
     these, aimed at the advanced amateur and the
     professional, are probably the Minolta Maxxum series
     and the Canon EOS. These cameras are packed with
     automation which allow automatic film advance and
     rewind, automatic and program exposure modes, and
     autofocus. Automatic focusing uses a system whereby a
     computer in the camera uses vertical lines in the
     subject and focuses the lens by analyzing these lines.
     I have not used autofocus systems in specimen
     photography but have experience with them for snap
     shooting. The problem is that if there are insufficient
     vertical lines in the picture, the focusing system with
     be fooled and can leave you with a terribly out-of-
     focus picture. I have stuck with manual focusing for
     specimen photography but would love to hear what the
     autofocus aficionados have to say about its use.
     
  2. Manual focus. In this method you simply view the
     subject through the viewfinder and turn a focusing ring
     until the subject sharpens. If you have a choice, I
     recommend a viewfinder with a split-field focusing
     prism to help with critical focusing, but others prefer
     a focusing grid, which, as far as I know, is only
     available on high-end cameras, like the Nikon F series.
     
B. Depth of field
  
  It is easy to focus on a flat object, such as a slice of
  brain, but things get stickier when photographing objects
  with depth, such as a windowed pediatric heart specimen.
  Shooting these subjects requires a knowledge of the
  concept of depth of field. It turns out that the zone of
  depth at which the camera is in focus is greater at
  smaller apertures (larger f/ numbers) than at larger
  apertures. Therefore focusing is very critical when the
  lens is "wide open" but much less so when "stopped down."
  Let's say you are shooting an opened colon to
  demonstrate, en face, a large villous adenoma. If you
  focused on the "top" of the tumor (the part nearest the
  camera) and shot the picture with the lens aperture at
  f/2, the tip of the adenoma would be in focus, but the
  sides would be slightly out of focus, and the surrounding
  colonic mucosa would be totally out of focus and probably
  not recognizable. However, if you stop down to f/16, the
  entire specimen would be in focus. Since this results in
  decreasing the exposure by six stops, you would have to
  compensate by increasing the exposure time by a factor of
  two to the sixth power, or 64. For good depth of field
  and optimal lens resolution, I use f/8 routinely and
  reserve f/16 and f/22 for subjects like the windowed
  heart. Most cameras have a "depth-of-field preview
  button" that lets you stop down the lens to its preset
  aperture, so you can view how much depth-of-field you'll
  end up with in the resulting picture (normally the
  aperture diaphragm stays wide open until the instant the
  picture is taken, so you have a nice, bright viewfinder
  in which to compose the shot).

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,

  1. The larger the image appears for a given distance.
  2. The farther away from the subject you can be for a
     given image size.
  3. The more critical the damping of camera motion to
     prevent blurring.
  4. The slower and more expensive the lens.
  5. The less the sense of depth and perspective.
  6. The less the curvilinear distortion of straight lines.
  7. The _more_ flattering to the face in portrait
     photography (makes face less moony and nose less
     prominent).
  8. The _less_ flattering to the body in figure
     photography (makes subject look stouter).
     
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:

  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 photography. It is rarely
  necessary to use anything other than a normal lens for
  our purposes except when shooting close-ups so extreme
  that the bulk of the lens shadows the subject, so that it
  cannot be illuminated sufficiently. In this case you
  need:
  
  80 - 135 MM (MEDIUM TELEPHOTO LENSES).These are used for
  high-magnification macrophotography 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. Operationally, the only thing special about
  these is that they 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 60 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, and Nikon's  much pricier 105 mm AF macro lens 
  allows a 1:1 focus). 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. If are absolutely set on using a zoom
  lens, you could try this: get a regular (non-macro) zoom
  lens which zooms by turning a ring rather than sliding a
  slide (i.e., a zoom lens which is not a "one-touch" zoom).
  Then put extension rings between the zoom lens and the
  camera. Extension rings are simply a set of tubes which
  extend the lens forward from the body of the camera.
  This will give you a zoom lens which focuses close-up
  but not far away. Extension rings can usually be had
  for less than $100. Appropriate zoom lens focal lengths
  would include 28 - 85mm and 35 - 105mm.
  
  BELLOWS. This is not a lens at all but simply a shade
  that extends the lens very far 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. Multiply
  this magnification by the amount you get when projecting
  a slide in a lecture hall and you get some idea of how
  Brobdingnagian a world you can present to an awed
  audience. 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.
  
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:

A. Cut away tissue that is of no interest, or that obscures
   the interesting features.
  
B. Use props to position the specimen when necessary. A
   slice of liver needs no props, but a gallbladder looks
   better when you shove a few wads of paper under the
   periphery to make it look like the saccular structure
   that it is. Modeling clay is also a good material from
   which to devise custom props.
  
C. Watch out for the obtrusive ruler. A lot of pathologists
   remonstrate incredulously when I tell them I almost never
   shoot a specimen with a ruler in the field. For one
   thing, no one has made a ruler yet that is as unobtrusive
   as I would like. Most specimens need no ruler, especially
   full organs or full organ slices. We all know how big a
   lung is; if not, we're only there for the free lunch
   anyway. If you really want to know how big the lesion
   was, just read the gross; it even gives all three
   dimensions! If you really want to impress the conference
   attendees with how big a goiter is, take a picture of it
   with an everyday object, such as set of keys. Or, better
   yet, bring the gross specimen to the conference and
   ceremoniously drop it on the table with a loud thud.
  
   I quit using rulers when I realized I never looked at
   them except to marvel at how distracting they were. I
   really don't think any one else looks at them either.
   But if you're so anal that I can never convince you to
   lose the ruler, do me a favor and shoot just one of your
   frames on each specimen without it. I'll guarantee you
   that nine times out of ten, that's the pic that you're
   going to want to show at the conference.
  
D. Keep the background clean. This is a real pain, but to do
   otherwise really compromises the photograph. It is much
   easier to keep things clean when dealing with a fixed
   specimen than a fresh, bloody one. On a related note, try
   to keep the camera clean. Layers of dried gore
   accumulating on the body of a tough Nikon F3 probably
   won't hurt the camera, but it tends to gross out certain
   people, particularly OSHA inspectors.
  
E. When photographing lungs or hollow viscera, use inflation-
   fixed specimens when possible. You have to resist all
   sorts of pressure from various circles to cut up the
   specimen when it is in the fresh state, but, then again,
   all great artists suffer for their work. I have yet to
   see a gross photograph of uninflated, unfixed lung that
   was any good. Inflation fixation of gut segments delays
   your diagnosis a day but rewards you with gross
   photographs that would bring tears to the eyes of any
   radiologist.
  
F. Try to get rid of as much blood as possible. Otherwise,
   the specimen ends up being just varying shades of red and
   pink.
  
G. Watch out for distracting highlights. Fresh specimens
   usually have very shiny surfaces that produce glare.
   There are several things you can do to cut the glare on a
   fresh specimen:
  
  1. Formalin dip for just a few minutes; this preserves
     color but dulls the surface; in overnight-fixed
     specimens which have lost their color, soak in 70% EtOH
     to partially recover color.
     
  2. Turn off room lights.
     
  3. Consider changing the lighting situation of your set-
     up. Nice copy stands are usually set up with four big
     floodlights. You may consider turning off the two on
     the front of the stand and leave the two on the rear
     on. Remember to adjust your exposure to accomodate the
     loss of these lights.
     
  4. Polarizer/analyzer filters do a great job, but the big
     polarizers that go between the floodlights and the
     subject are very expensive and fade out fairly rapidly.
     
H. Photographic backdrops. The choice of a proper backdrop
   is essential for a professional looking photograph. The
   best background is the one no one knows is there. Several
   options are available:
  
  1. Transilluminated light board with non-glare glass -
     expensive; klutzes drop things on the glass and break
     it; departmental business manager is incredulous at
     expense of replacement and usually stalls its purchase.
     
  2. Wet black velvet - less expensive ($12/yard); reusable
     for a long time if you're careful; keep fresh, bloody
     tissue off! Give each resident his/her own piece. Of
     course, if you shoot anything that may have infectious
     agents on it, you can't re-use the velvet, unless you
     can find a way to sterilize it (another argument in
     favor of shooting only fixed tissue).
     
  3. Water immersion tray - Incredible shots of delicate,
     "three-dimensional" objects make you into an amateur
     Lennart Nilsson; solves problems of gravity and glare
     simultaneously for such objects as villous adenomas,
     chorionic villi, emphysematous lungs, etc. In my
     experience, it takes quite a bit of patience to get a
     good shot, as undesirable bits of grunge tend to float
     into the field of view just as you are releasing the
     shutter.
     
  4. Towel from surgery - sure sign of an amateur; an
     embarrassment to say the least. However, if that's all
     you've got, ask for a clean towel to replace the bloody
     one they handed you the specimen on.
     
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.

A. Color transparency film. These yield the 2" x 2" mounted
   transparencies known affectionately as "kodachromes" (in
   the way that facial tissue is known as "kleenex"). The
   actual frame size of the transparency is 24 x 36 mm.
  
  1. E-6 process color reversal film (Ektachrome,
     Fujichrome). Compared with Kodachrome (see below),
     these are expensive; they have quirky color response
     (being notoriously poor in rendition of eosinophil
     granules, which look kind of dull purple rather than
     vivid orange), and the slides fade with time (although
     this may not be true of newer films in this category).
     Nevertheless, the E-6 films are by far the most popular
     in med center settings because of the ready
     availability of the E-6 process. Most professionally
     oriented processors can routinely turn around the film
     in four hours. With a readily-available kit, you can
     even process these films at home for about US$3 per 24-
     exposure roll (plus a one-time US$30 investment for a
     developing tank and reel).
     
  2. Dye injection film (Kodachrome). Kodachrome is
     superior in every way to the E-6 films, except that the
     processing is slow and is usually done in large
     reference centers where the film must be sent.
     Eosinophils look great, and the slides last essentially
     forever if stored properly. It is difficult to find
     tungsten versions of Kodachrome, but the daylight
     versions can be shot under tungsten illumination if a
     special filter is used.
     
B. Color negative film (Kodacolor, Ektar). Also generally
   available only in daylight versions, these films yield
   color negatives which must be printed. It is preferable
   to use color negative film for posters, rather than
   having color prints made from your transparencies. This
   is because color prints from transparencies usually
   suffer from enhanced contrast that compromises the
   accuracy of the rendition. When having color prints
   processed, you must work closely with a skilled print
   processor for good, publication-quality prints. The
   automated printing machines used in "one-hour" facilities
   are not capable of producing an accurate print from a
   color negative of scientific subject (unless, perhaps, it
   is a portrait of the scientist).
  
C. Polachrome film. This abomination of a transparency film
   develops in a few minutes in a processor you can keep in
   your desk drawer. It is extremely expensive, and the
   dense emulsion makes slides too dark on projection; the
   colors are less than impressive. It is best not to let
   the clinicians know you have a Polachrome processor. They
   will start giving you the conference cases even later and
   will not realize how lousy the pictures are, while you
   are grinding your teeth trying to find that audience-
   pleasing mitosis somewhere on the screen.
  
D. Black-and-white film. Not to go into this at any length,
   but you should use this for originals to be used for
   publication. Black-and-whites made from color negatives
   or transparencies are generally second-rate. Also you can
   experiment with color contrast filters, which can really
   improve results.
   
NOTES ON PURCHASING PHOTOGRAPHIC EQUIPMENT

1. Only a fool or the government pays retail for photographic
   equipment.
2. The best prices are available via mailorder. You can find
   ads for these companies in any photography-oriented
   magazine.
3. The only drawback to mailorder is that you have to know
   exactly what you want when you order it. Mailorder outfits
   are notorious for bait-and-switch. Decide what you want
   by reading and talking with other photographers before
   calling to make the order; otherwise, you _will_ be taken
   to the cleaners by these extremely effective salespeople.
4. Don't pay any attention to brand-specific chauvinism.
   Many photographers are quick to look down their noses at
   any brands other than Nikon, Canon, Hasselblad, and Leica.
   I think you will be very pleased with other brands, for
   which you will pay a _lot_ less money. The major factor
   which determines the quality of photographs is the skill
   of the photographer, not the brand of the equipment.
  
                      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.

Norbert Fuerst sent me some good information on macro and
zoom lenses.

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. 

_______________________________________________________________

An HTML version of this FAQ is available through the author's home
page at:

               <http://www.neosoft.com/~uthman/>


                          IMPORTANT
                              
Please send any constructive comments about this paper to Ed
Uthman, <uthman@neosoft.com>. 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."

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