Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay
I've taken a lot of ribbing over the years for always being there with a camera, only to have people ask if they can get a copy of this or that shot. Despite having a slide archive of about 30,000 pictures (and at least as many digital), I often find I do not have a picture of some particular place or thing, or at least not a picture that exactly meets my needs.
YOU CAN NEVER TAKE TOO MANY PICTURES. Film is cheap, digital imagery is virtually free. Plane tickets and trips to remote places aren't, to say nothing of the time cost. And even if you can go back again, will the scene still be there in 20 or 30 years? Will it be quarried away, buried under mine tailings, grown over, fenced off, flooded, carried off in a landslide or paved over? Will roads and bridges still be there? Even if the locality is still there, it might be valuable to be able to compare it to its appearance years earlier. YOU MAY BE THE ONLY PERSON EVER TO PHOTOGRAPH A PARTICULAR FIELD LOCALITY. Even if you can go back and the scene is still there, will you be physically able to go someplace at the age of 50 that you got to at 25? If you don't get the picture when you climb Half Dome at age 25, will you be able to climb it at age 50? TAKE THE PICTURE WHEN YOU HAVE THE CHANCE and err on the side of overdoing it.
SHOOT THE ORDINARY. A whimsical set of "Laws of Field Geology" holds that the likelihood of getting a specimen is inversely proportional to the abundance of the rock, and that a corollary is that the whole field season may pass without getting a specimen of the most abundant rock type. Ditto photographs. Shoot pictures of typical scenery and outcrops in addition to the more interesting and exotic things.
The best way to get great photos with cameras of this sort is as follows:
In fairness to the disposables, I once had an expensive camera break down on a trip and bought a cheap 35-mm camera in desperation. I was amazed at the quality of pictures it took. Given that the lenses are often molded plastic, they are surprisingly good. However, cheap cameras have serious defects:
Bottom line: you can't do serious field photography without being able to control exposure and focus, and that means a single-lens reflex (SLR) film camera or a good digital camera. In the field you may need to get within a couple of inches of your subject and that means you must have a camera where you can see exactly what is in view. It costs a lot of money to do a field study. Cameras and film are not the place to economize.
By the way, learn to see. People with digital cameras and SLR's still take pictures with telephone poles sprouting out of people's heads. Don't just use the viewfinder to aim; actually observe what is there.
Once upon a time, before one-hour automated film processing, slides were cheaper than prints. Now the reverse is true. With video cameras and computers, people who want to show pictures to a group most often shoot video or digital pictures rather than slides. Thus, slide film is not as widely available as it once was. You may not be able to find it in a supermarket or department store.
I recommend slide film for all serious field photography for two reasons:
The two points above guarantee that there will be a niche for slides for the foreseeable future. In fact, slide films continue to be improved and introduced in new forms. However, the ready availability of scanners and digital photo printers makes this distinction less critical than it once was. If you have to resort to print film you can easily scan the negative or print and get a slide made.
Since I got a digital camera in 1998, my use of film has dropped at least 95 per cent. For most of the pictures I shoot, digital photos are acceptable quality. Only if I suspect I might ever need to publish a photo or show an extremely high quality image do I shoot film. One advantage of digital photography is that you can know immediately whether or not you got the shot. You may find out too late with film that something went wrong.
For the best films, the resolution on film is about 100 line pairs per millimeter. That means for a standard 35-mm frame (36 by 24 mm), the effective resolution is 7200 by 4800 pixels (36 or 24 mm times 100 line pairs per mm, times two pixels - one for each line and one for the space between). When I did some test scans of some good sharp slides, they seemed to show that about 2400 pixels across captured all the detail physically present in the slide. Why 2400 instead of the theoretically attainable 7200? I suspect the reasons include:
So, if you shoot on a tripod, using the most perfect focusing methods imaginable, and you've checked to make sure the focus on the film plane is exactly correct, and you are using absolutely the best lenses made, you might get resolution approaching what the film can theoretically do.
The comments below are written in film terms. You need to know this even if you only shoot digital because many digital cameras express their capabilities in film terms.
Film speed is measured by a numerical scale called ISO (older cameras and books refer to it as ASA). The higher the number, the more sensitive the film is to light. In 1970, Kodachrome film had a speed of 25. Nowadays 100-speed is the norm, with 200 and 400 available for low-light situations. Films with ratings in the thousands are available. Airport X-ray units usually state they will not affect film with speeds below 1000. You need to know this even if you only shoot digital because many digital cameras express their sensitivity in terms of ISO equivalent.
Films vary in the way they record images, and the same scene shot with two different films will have a different color cast, even though each picture viewed in isolation may look perfectly natural. Color balance is most likely to show up in extreme lighting situations such as nighttime shots.
Pictures taken under fluorescent lights typically have a strong green cast. The eye is very good at correcting for color balance, which is why we often are surprised by what shows up on film. Pictures taken under incandescent light often have a strong orange cast. If you take a lot of pictures under those conditions, you can buy tungsten-balanced film to correct the color. Digital cameras often have settings to correct for these situations.
Photos taken through car windows can have a perceptible green cast even if the scene looks perfectly normal to the unaided eye. The adaptability of the eye means we often don't see color variations that film and digital images record.
Good cameras will usually have a wheel that sets the shutter speed. A typical wheel will be marked B, 1, 2, 5, 10, 20, 50, 100, 200, 500, 1000, where the numbers stand for fractions of a second. Thus, 200 means 1/200 of a second. B stands for "Bulb" and is used for taking time exposures. As long as the shutter button is depressed, the shutter stays open. The name is a holdover from the old days when an air bulb was used to trigger shutters without touching the camera. Some cameras may offer exposures longer than one second or shorter than 1/1000 second.
The aperture is the size of the opening that admits light. Aperture and shutter speed both control how much light reaches the film. If you decrease the aperture, you must increase the exposure time.
Focal length is the distance from the lens to the film. The longer the focal length, the larger the image, but the narrower the field of view. Most good cameras have lenses with focal lengths about 50 mm. Anything longer is considered a telephoto lens, anything shorter a wide-angle lens. You might think that since a human eyeball has a diameter of about 50 mm, a normal camera lens pretty well matches what the eye sees. In fact, tests have showed that it takes about a 100-mm lens to match what the eye sees, say by comparing photographs with paintings of the same scene. The reason is that the active imaging area of the retina is a lot smaller than the area of a 35-mm picture frame. Compared to a typical camera, the eye is a telephoto lens. In fact, when we zero in on something like the rising moon, our field of view shrinks even more. This is why so many photos of airplanes, birds, and the moon come out as just specks whereas the eye saw a great deal of detail. It takes maybe a 500-mm telephoto lens to capture the same impression as the eye in such cases.
Now here's the important part. A long focal length lens creates a larger image than a short one, which means it spreads the light out over a larger area. Thus the image is dimmer. To create an image as bright as with a short focal-length lens, we must increase the aperture. The f-ratio is the ratio of the focal length to the aperture. For example, a 100-mm lens with an f-ratio of 4 has an aperture of 100/4 = 25 mm. Images formed by lenses of the same f-ratio are equally bright, regardless of the focal length. Put another way, the f-ratio dictates the intensity of the light falling on the film.
(This simple definition of f-ratio applies to a simple lens, like a magnifying glass. For camera lenses, which can often be complex systems of lenses and mirrors, the scale of the image determines the effective focal length.)
F-ratio governs something else besides image brightness. The smaller the aperture, the greater the range of distances that are in acceptable focus. If you're shooting a portrait of a person a meter away, at f-2 the person's cheeks may be in focus but the tip of her nose and her ears might be fuzzy. At f-16, not only is the entire face sharp but distant background objects might be as well.
Depending on circumstances, you might want minimal depth of field or very great depth. For a portrait, a sharp background might be a distraction. On the other hand, when taking a picture of an irregular rocky outcrop, you probably want the whole picture to be sharp.
Logically, the tinier the aperture, the greater the depth of field, and a pinhole should result in absolute sharpness. In theory this is true, a pinhole camera has everything in focus. In reality, there's another phenomenon, diffraction, that makes images fuzzy when viewed through small apertures. Diffraction starts to show up around f-8. Pictures taken at f-16 have great depth of field, but the sharpest focus isn't quite as sharp as the same picture taken at f-5.6. There's a trade-off.
One place depth of field gets serious is in copying documents and slides. If you zoom in on a segment of a map, the center of the picture will be significantly closer to the lens than the corners, and you may well see fuzziness at the corners of the image. Focus will vary, also, if your line of sight is at all oblique to the map. The same problem arises in copying slides with a normal camera lens. If you can do it at all, perhaps with a close-up attachment, you can only do it by getting very close to the slide. If you don't use special lighting, you'll probably need a low f-ratio, making the depth of field problem worse. You can reduce these problems by getting further away from the object you're copying and using bright lighting, but you may well need a zoom lens to get the desired image scale.
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Created July 20, 2000, Last Update July 21, 2000
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