This is part 6 of a 6 part series on getting to know your digital camera. Read part 5: Aperture Priority.

So we’ve seen how aperture setting (also referred to as the “f-stop”) and shutter speed control the amount of light reaching the film (or digital sensor). A theoretical proper exposure requires the right combination of aperture and shutter speed. The combination can be adjusted for a variety of purposes:

Shutter speed refers to the speed at which the shutter exposes the film or (digital camera CCD) sensor to light. Fast speed (1/500 sec.) captures motion; slow speed (1/30 sec.) blurs motion.

Aperture refers to the size of the lens diaphragm’s opening. A higher f-stop (f8) lets less light in to the film or sensor than a lower f-stop (f2.8). In other words, a higher f-stop means a smaller aperture. This affects the image’s depth of field, or the range of subject-to-lens distances that will be in focus. The higher the f-stop, the greater the depth of field.

Most cameras have a manual mode (indicated by the “M” on the dial) for “manual” setting of the exposure. In this mode, you are expected to choose both aperture and shutter speed. The camera generally will indicate to you whether there is enough light to properly expose the film/sensor (this is key!). Not only does manual mode allow you to be the most creative with your exposures, but it is also a great way to learn the best combination of aperture and shutter speed for the type of shooting you do. For instance, if you’re shooting cemetery photos in New Orleans during Hurricane Katrina, you want a fast shutter speed. Unless it’s a bright sunny day, this would force you to use a shallow depth of field (which is what you want anyway).

Digital cameras shorten the learning curve by giving you instant feedback, by way of the picture display. You can get a general idea whether your technique is successful by looking at your result. There’s no lag time between cause and effect, like there used to be when you had to get film processed

Now, there’s just one more concept you need grasp to help you to use your camera effectively–ISO.

ISO refers to light sensitivity (ISO stands for International Standards Organization). Formerly called ASA (American Standards Association), these numbers used to denote film speed, most commonly from very “slow” low ISO films (100) to the “ultra fast” high ISO films (1600). Low ISOs for bright sun, high ISOs for indoor or other low-light situations. Generally you can set ISO in any mode.

That’s almost interesting, right? Why bother? Well, if you shoot at a low ISO, you get a sharper, less grainy/noisy image. The trade-off with being able to shoot in low-light situations is that the image becomes less sharp, more grainy/noisy. Physical limitations of the technology, I’m afraid. However, this can work to your advantage if graininess is your desired effect. Personally, I prefer it for shooting cemetery statuary. It gives the image a more gothic effect.

Practical Tips
Let’s start out by setting the film speed indicator to 100. This is recommended for outdoor photography in bright sun. Now set your mode control to “Av.” To review, the aperture priority mode allows you to choose an aperture setting, and the camera automatically sets the shutter speed.

Now, compose a shot outside, using a high f-stop (like f10). Note the shutter speed your camera chose. Let’s assume it is 1/250 second. Change the ISO setting to 400 and compose the same shot. At the same f-stop as before, what shutter speed has your camera chosen? Perhaps it is 1/1000 of a second. This is because for a given aperture, the camera’s light sensors have been made more sensitive, allowing for a shorter exposure time.

Why not just keep your ISO high all the time? While a fast shutter speed allows you to handhold the camera in low-light situations, a high ISO setting produces noisy digital images (just as high ISO, or “fast” film produces grainy images). See the examples to the left.

A word of warning — a high ISO setting can make your camera overly sensitive to light! See the overexposed image below. This was actually a statue on a mausoleum at the Metairie Cemetery in New Orleans. I shot it on a bright sunny day at too high of an ISO. The effect is not without its charms, but it was unintentional!

Helping you take better pictures was the goal of this article. The principles apply to both film and digital. To summarize, while digital cameras are wonderfully flexible devices, they are not magical. The basic photographic principles of aperture and shutter speed hold true for digital and film cameras. Both types of cameras have wonderful assets, and both present challenges to us with their technological limitations.