There are few differences in the light sources used with medium and large for-mat versus 35 mm (see Chapter 6). Because of the potentially longer exposures with large-format cameras, it may be necessary to use stronger light sources than you would for 35-mm work.
Some large-format photographers pre-fer to use studio flash because it minimizes vibration problems. I use mostly flash and find that for small subjects at small aper-tures, one pop of the flash may not be ade-quate. I use a fairly powerful unit of 2400 watt seconds and find that the average sub-ject requires two to four pops of the flash at full power. This illumination may sound like a lot until you consider the light loss from using the main light in a soft box, shooting at f-45, the long bellows exten-sion, and splitting the power with another head that is used for a background light.
Incandescent or "hot lights" are pre-ferred by many photographers. They are much more controllable and come in a wider variety than flash. Incandescent lights are also less expensive than studio flash, especially if you use spodights and fiber optics.
METERING
Most medium-format cameras have built in metering just as 35-mm systems do, so there is no difficulty there. On the other hand, large-format view cameras do not 32
contain metering systems. Metering is usually done with a handheld meter, with the standard calculations to take into account bellows extension. Taking Polaroid test shots is extremely useful as a check of exposure. However, warning concerning the use of Polaroid test shots for exposure determination is in order here. It is wise not to rely on the Polaroids for exposure determination. Just as differ-ent batches of one type of film can vary, so can two different types relative to each other. Theoretically, an instant film with the same ISO as the film you use for the actual shot should produce a comparably exposed picture. In reality this is seldom the case. Use of a good light meter that you are familiar with should be the basis for exposures, not Polaroids. Use of instant photos for exposure checking should be one of their minor functions.
I've found that the Type 55 ISO 100 black-and-white Polaroid film 1 use is fairly consistently l/3 stop faster than the Kodak Ektachrome 100 Plus film that I use for most of my work. That doesn't sound like much, but since 1 bracket in
l /3 stop increments, it is significant.
There are several light meter manu-facturers who produce a meter with a probe. The probe can be inserted into the film plane for accurate spot metering.
Several readings can be taken and aver-aged if necessary. Just as with built-in meters in 35-mm cameras, the use of such a probe means you do not have to make calculations for bellows factors.
(See also Chapter 9).
MAGNIFICATIONS
Magnifications are achieved with medi-um and large format the same way as with 35-mm cameras (see Chapter 12).
Macro Tenses, extension tubes, and bel-lows are available for many of the medi-um-format systems.
There are no special bellows needed for large-format cameras. The further you extend the bellows, the greater the magni fication. A point will be reached where the bellows will extend no further, either because you run out of rail, or because that is the maximum extent of the bellows.
To extend beyond that point you need to add another length of rail, and/or another bellows. Additional rails are easy to add, usually just by screwing on another length.
Very long rails can get unwieldy and require the additional support of another rail clamp on a connecting base plate. The addition of another bellows means the use of another front standard as a connecting device and to prevent sagging of the long bellows assembly.
Just as with smaller formats, standard lenses are not designed for close-up and photomacrography. Special macro lenses are made for view cameras. They are rarely available in focal lengths shorter than the standard lens (ca 150 mm). There are lenses of a shorter focal length that require less extension, such as the Zeiss Luminar lenses.
While use of short focal length lenses reduces the need for long extensions and attendant long exposures, their use has some disadvantages. Foreshortening of the subject is undesirable, and the
work-ing distances can be miniscule. With a 50-mm lens, 1 found my lens-to-subject distance was less than 2 cm.
The use of other lenses, especially enlarger lenses, can yield excellent results as they do with smaller format cameras.
To keep working distances reasonable, keep focal lengths longer than 90 mm. A problem with enlarger lenses is that they seldom stop down beyond f-22. This is a serious problem because the use of small apertures is necessary for maximum depth-of-yeld in photomacrography.
Since enlarger lenses were not designed for use with view cameras, they may not be able to cover the image arca once you start using extreme movements.
Specialty macro and enlarger lenses do not contain shutters, so exposures must be taken another way. The dark
slide is removed in a darkened room, the lights turned on for the proper exposure duration, the lights turned off, and the dark slide replaced.
FILTRATION
The filters for medium-format cameras screw onto the front of the lens the same as with 35-mm cameras. Gelatin filters can also be used with the appropriate fil-ter holders.
Most filters for large-format cameras are gelatin and must be used with holders that do not attach directly to the lens.
Because gelatin filters are more prone to damage than glass filters, some photographers minimize their potential for image degradation by attaching them to the back side of the lens. (See also Chapter 10.)
34
GENERAL
CONSIDERATIONS
n any type of photography, film choice is important and is dependent on subject material, lights, and the use of the photographs. Color film is
usu-ally the choice for mineral photography because of the incredible range of colors found in the mineral kingdom. On the other hand, some photographers feel that black and white is better because it forces you to work more with form, line, and texture. If you have your own darkroom, black and white is less expensive and easier to work with, and you have much greater control over the results.
The speed of a film is a measure of its sensitivity to light. The higher the num-ber, the greater the sensitivity of the film.
Film speed is designated by an ISO num-ber (formerly ASA numnum-ber). In a film des-ignation of ISO 64/19º the number 64 is the ISO number, an arithmetical mea-sure, and the second number is the European DIN speed, which is a logarith-mic measure. In this book I refer to films
only by the ISO film speed designation.
Films with low ISO numbers general-ly are better choices than those with high-er numbhigh-ers. Though they are less sensi-tive and slower, resulting in longer expo-sures, they have advantages over faster, more sensitive films. Slower films have much finer grain and better color rendition.
Fine grain is especially important if you plan on making large prints, and accurate color rendition is important for proper representation of a specimen.
Most films are DX coded, which means that the canister has a pattern of black and silver squares that is read elec tronically by the camera. The code tells the camera what the film ISO is, so if you forget to set the ISO on the camera, you will still get proper exposure. There is also a bar code on the canister as well as on the film itself. In addition, there may be raster (hole) pattern on the film leader.
These codes give the film-processing labs necessary information.
Slower films have much finer grain and better color rendition.
Fine grain is especially important if you plan on making large prints, and accurate color rendition is important
for proper representation of a specimen.