Film comes in two versions, negative and positive. Negative or Print films produce an image that is the exact opposite (in terms of color) as positive (slide) films. The purpose of a negative film is to allow you to make a positive print, or photograph. Because the paper used to print the negatives also makes a negative image, if you print with a negative film on a negative paper, you get a positive print. Got it?
Positive films (hereafter called slide film) form a positive (normal) image on the film itself. This is useful if the image is going to be projected. It is also nice if you are viewing the image directly, but since the film is so small this isn't really a consideration. Experienced photographers using a loupe (magnifying glass) are experienced at judging both slides and negatives on the light table.
Which is better? Several factors must be considered before making a choice.
Which to buy? If you need to project, you need to use slides. For other purposes, investigate local costs of film and processing before making a decision. If you plan ahead, you can often save money buy purchasing larger quantities of film on-line or by mail order (be sure to buy enough film to offset the per-roll cost of shipping and handling).
In a perfect world, film would have no grain at all. In our world, grain is a fact of life. The light-sensitive chemicals that form the image take up a certain amount of space. The bigger the individual chunks of light-sensitive chemicals are, the grainier the film. Unfortunately, there is a positive relationship between grain and film speed. The faster the film, the grainier it is.
Grain is bad because it reduces resolution. Resolution is the ability to distinguish between two close points, but if you have large grain those close points may wind up on the same chunk of chemical - and thus the ability to distinguish between them will be lost. Fast film is better because it allows you to freeze fast motion with high shutter speeds, or increase sharpness and depth of field by using a smaller aperture. Unfortunately, you can't have your cake and eat it too.
Deciding on a film speed is largely deciding where to compromise. Most nature photographers working today tend towards slower films to get the best possible resolution. The standard seems to be films in the 50-100 ISO range. The professionals make up for the slow film speed with technique - extensive use of tripods to reduce camera shake, using mirror lock-up features, timing photographs to catch the moment when the action is at its slowest, photographing when the light is best, using flash. Until you learn these techniques, you might want to drift up to faster films in the 200 ISO range. Stay away from 400 ISO or higher films unless you really need them. You will be disappointed in the results because of the grain. Also, higher speed films (at least 400 and above) often cost more. BY the way, if you need a film over 400 ISO, you might want to consider a print film.
Nowadays, most imaging is done in color. Remember that the technology to produce color film and process it was not practical on a large scale until World War II. For a long time, most photography was done in black-and white. In general, black-and-white films are cheaper, they have smaller grain at a given ISO, and they can be processed with simple chemicals, even in a home darkroom. But, of course, the final result is black-and-white, and we live in a color world.
Black and white photography still has its place, however. If your ultimate product will be printed in a black and white publication, it may be cheaper and easier to work with black and white throughout. Or, if you will be doing some of the printing yourself, it is much easier to work in black and white. Some black and white films and papers are unmatched for resolution and/or contrast.
Paradoxically, in today's color world, it is getting harder to find places to get black and white film processed. Recently, some film manufacturers have begun producing black and white film that can be run through machines designed for color film.
You will see "Professional" film advertised in magazines and online. What is it? Basically, professional films differ from "amateur" films or "consumer" films in several ways. First, they are made in larger batches. Because film can differ slightly from batch to batch, professionals like to stock up with large numbers of rolls of the same batch of film. This way, there is less difference from roll to roll. Secondly, professional film is stored under better conditions than the average consumer film. It is usually held in refrigeration from the factory to the store. Refrigerating the film helps extend its life beyond the "expiration date" stamped on the film. Third, some professional films do have differences in light sensitivity or color rendition as opposed to the comparable amateur films. Finally, professional film is packaged in bulk and thus has less packaging than the consumer equivalent - a good environmental feature.
Are they worth it? Personally, I don't see the differences between batches of film (I'm hard pressed sometimes to tell the difference between different films period). I do like to buy a lot of film at once, however, and I do store my film in the refrigerator. In the end, if I can get a deal on the professional film I'll buy it, otherwise I go with the consumer-grade film.
There are other types of film out there. Of course there is Polaroid film, which gives you instant prints (but not in a 35 mm format). There is also Polaroid slide film which you can process yourself (our department is equipped to do so) if you are in a hurry. Infrared film is sensitive to infrared light. Most infrared film is black and white, but there is false-color infrared film available. Infrared does not focus at the same point as visual light, so auto focusing is out, and manual focusing is a guess. Some cameras, such as Canon EOS cameras, use an infrared LED to count film sprocket holes; these may fog infrared film. UV film is also available but very hard to find. Tungsten film is specially balanced for use with incandescent lights (which give a yellowish cast to normal films). This film is good for work on the copystand or in photomicroscopy.
Photoworks and several other companies sell a film which is advertised to give you both slides and negatives from the same film. Yes, this really works, and the quality isn't all that bad. There are several things you need to be aware of, however:
Once film has been exposed, it must be processed. This makes the image appear and makes the film insensitive to light, so that it can be viewed. For color films, there are three main processes that are used. C41 processing is for color print film; E6 is for most slide film, and Kodachrome processing is for some slide films.
Most one-hour photo stores have machines which can do both the C41 processing of film and the subsequent printing of prints from the film. While the chemistry, temperatures and timing required are precise, automated machines with embedded computers can easily handle this. Most stores can do an adequate job of processing the film, however there are large differences in their ability to make good quality prints from the film. If your one-hour photo center does not do a good job with the prints, you might want to pay a little more to have the film processed at a camera store. If you will be scanning your images into a computer using a film scanner, you may want to save money by having them do "negatives only".
E6 processing is a little harder to find. Most camera stores will offer it, and if they have a machine on-site, may be able to offer 1-hour E6 processing.
Kodachrome processing is very demanding and only a few labs offer it. You will almost certainly have to send your Kodachrome film in to one of these labs for processing.
You can do black and white, E6 and C41 processing at home. Minimum requirements are a darkroom (unexposed film must be handled in TOTAL darkness) or changing bag, film developing tanks, thermometers, timers and the chemistry. If you shoot a lot of film and if you like working in the darkroom you can save a little money by developing film yourself.
Finding a reliable processor isn't always easy. When you get an order back, check carefully. Are the prints well-done, with details in the highlights and the shadows, and good color tone? Is there a color cast to the prints? Are the negatives or slides clean and unscratched? Are slides mounted straight? Is the service timely and economical?
To increase the ISO of a film, you can push film. This simply means developing it for a longer time. The results can be quite good; for instance you might be able to push a 50 ISO film to ISO 100 and still have less grain than an ISO 100 film developed normally. Here's how to do it:
After its expiration date, film will begin to show a shift in light sensitivity and color rendition. To keep your film fresh, store it under the proper conditions:
Speaking of airports, those lead "film safes" sound like a good idea. But consider this. You are operating an airport luggage x-ray, and a bag comes though with an opaque square in the center. Do you:
Myself, I put the film in a plastic bag (in see-through canisters) and hand it to the agent. I let my cameras (and any film in them) take their chances with the x-ray. It's worked for me so far.
Here are some recommendations for film. The prices are for comparison only; they were current as of July, 2000. All costs are based on a 36 exposure roll. I have added comments on films I have some experience with.