How to Do Everything with Your Digital Camera in Software

Generation QR Code in Software How to Do Everything with Your Digital Camera

The two kinds of film in common use today are negative and slide film They work a little differently, but the end result is similar When you use color negative film, also referred to as reversal film, the film itself becomes a negative image of the scene you photographed After processing which includes letting the film sit in a chemical bath that coaxes the grains of silver to visually materialize on the film the negative is used to create positive prints of the scene It s a two-step process, and one that is highly subjective When creating prints from negatives, photo-finishers often tweak the picture to improve its appearance Of course, what the corner shop considers an improvement may not be what you were trying to achieve, and that explains why your pictures never seem to benefit from filters, exposure changes, or any of the other corrections you try to make when taking pictures But I digress The other kind of film is simple slide film This is a color positive development process after fixing the slide film in its chemical bath, the film becomes slides that can be held up to the light to display images No matter what kind of film you have, it eventually needs to be exposed to light When you take a picture, you obviously press the shutter release The shutter release instructs the camera to open a diaphragm in the lens for a brief period of time and then close again If all went well, that was just long enough to properly expose the film If you want to shoot with 35mm film, scan the results, and then edit and print the results on your PC, you might want to work with slide film Slides are more exacting they require you to nail the exposure fairly precisely, as I explain in 11 but they ll better represent what you actually photographed instead of the local photo shop s vision of what you photographed

As you no doubt know by shopping for film, not all canisters of 35mm film are alike Film is differentiated principally by its speed, or ISO number A film s ISO number refers to how sensitive it is to light The lower the number, the less sensitive requiring long exposures or very bright scenes The International Organization for Standardization (ISO) is the group that helped establish how the number scheme works Film around the world uses ISO numbers, so you can buy it anywhere, and it ll all work the same In the United States, photographers used to call this system ASA, which stood for the American Standards Association That term was essentially abandoned about 20 years ago, so if you want to be considered a gristled old geezer, you can refer to ISO numbers as ASA A fairly typical ISO number for ordinary daylight photography is ISO 100 Increasing the ISO to 200 doubles the sensitivity of the film; dropping back to an ISO of 50 halves the sensitivity of the film This film sensitivity has a tangible effect on the mechanics of photography To see why, look at Figure 2-1; this diagram shows a typical camera body as a picture is taken The lens is equipped with a diaphragm called an aperture that has a certain diameter and consequently

FIGURE 2-1

is designed to allow a specific amount of light through to the film With ISO 100 film in specific lighting conditions (say, at midday) the shutter might need to open for a 250th of a second (1/250) to adequately expose the picture But what happens if we instead try to take the same picture with ISO 200 film The film is exactly twice as sensitive to light as the previous roll of film And that means, all other things being equal, that we need to leave the shutter open for only half as long (a 500th of a second, or 1/500) to take the same picture That s not all Suppose you re trying to take a picture in late afternoon when there isn t as much light available You might need to leave the shutter open for 1/30 in that situation to gather enough light That shutter speed is a bit on the slow side, though Not only might you jiggle the camera as you re taking the picture (it s hard to hold a camera steady for 1/30), but your subject might move as well, causing a blurry picture You can probably guess what the solution is stepping up to ISO 200 film will enable you to grab that picture at a much more reasonable 1/60, and ISO 400 would halve the shutter speed yet again, to a crisp 1/125