Last week, we began a review of digital-photography basics by briefly covering the camera's image sensor and pixels, photo file formats...
Last week, we began a review of digital-photography basics by briefly covering the camera’s image sensor and pixels, photo file formats and compression. This week, we’ll cover aperture, shutter speed, lenses, noise, ISO and more.
The purpose of this minitutorial is to help you (and me) understand a little more about how digital cameras work, so that we can make better choices about what camera to use and how to create better-quality photos.
Of course, it takes more than two short columns to explain digital photography. What this summary leaves out, you can find in these books: “Real World Digital Photography” by Eismann, Duggan and Grey; and “PC Magazine Guide to Digital Photography” by Grotta and Grotta.
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Aperture and shutter speed
The aperture is the size of the lens opening that lets in light; shutter speed is how long the lens stays open. Most cameras automatically make these adjustments for you, and better cameras also enable you to adjust the settings yourself.
There’s usually enough light to shoot outdoors during the day. But when the sun goes down or the photographer goes inside, the challenge begins.
Using a flash provides light, but such strong, direct lighting isn’t as natural (or flattering) as gentle light that surrounds the subject.
I prefer to shoot without a flash, using compensating settings for aperture and shutter speed. For example, if I use a reasonable shutter speed for hand-held shooting (1/60 or 1/100 of a second), I’ll still need to open the lens wide with an aperture setting of f/1.8 or f/1.4 (as the number decreases, the aperture opening increases), though these settings are rarely available in consumer cameras.
In fact, I’ve found it difficult to get a clear picture of active subjects indoors without noise or blur. Even if an image looks OK printed at 4 x 6 inches, it won’t if enlarged much more.
The lens plays an important role in image quality. According to “Real World Digital Photography,” the sharpest images — ones that maintain maximum detail from highlights to shadows — always start with high-quality lenses.
Lenses with an aperture range that includes f/1.8 or f/1.4 can let in maximum light and are called fast lenses. They enable the photographer to shoot in low-light situations without a flash; they’re also more expensive.
Consumer cameras generally use fixed lenses rather than interchangeable ones, and those fixed lenses typically have zoom capabilities.
However, “Real World” notes that moderately priced zoom lenses generally aren’t as fast, don’t provide the same maximum aperture across the zoom’s range and generally don’t produce as sharp images as non-zoom (prime) lenses.
Digital cameras typically have both optical and digital zoom capabilities. The advice is not to use the digital zoom because it’s equivalent to cropping the picture; it simply cuts away pixels.
Use the optical zoom, and save cropping for the editing process.
Noise in digital photography and grain in film photography are often perceived as equivalents, but they’re a little different.
Grain is the tiny, kernellike film particles that become visible when the film is pushed by a high ISO (see below) or enlargement. A little grain may be viewed as a flaw or an asset for creating a mood.
Noise is the tiny random artifacts on a digital image caused by interference and electronic errors in the camera. Using a high ISO or enlarging the image increases the noise and is seldom viewed as an asset.
In film photography, ISO (International Organization for Standardization) rating is a measure of the sensitivity of the film.
The higher the ISO rating, the more sensitive the film is to light, so that less light is needed to capture an image.
In digital photography, ISO rating is a measure of the sensitivity of the image sensor, which determines the sensitivity of the pixels.
To accommodate a higher ISO setting in the camera, the signal from the pixels must be amplified to provide information when there’s little light. The amplification causes noise; some cameras are better than others at minimizing it at high ISO settings.
A larger image sensor with larger pixels can absorb more light, giving the camera a higher overall ISO rating. However, larger pixels are not as able to capture as much fine detail as smaller pixels, according to “Real World,” so smaller pixels are desirable for attaining sharp images.
It seems the best pixel size is a balance between the ability to capture fine detail and minimize noise at a reasonable ISO setting.
That’s a tough balance to achieve. Camera manufacturers are still working on it, so we see newer and better models introduced every year.
Compact or DSLR camera?
Judging from reader mail, it appears some of you (like me) feel limited by the current consumer models and are considering moving up to a digital single-lens-reflex camera.
DSLR cameras support high-quality interchangeable lenses, have a larger image sensor, higher ISO options that reportedly produce less noise, a larger range of shutter-speeds, and are technically more able to produce better-quality photographs.
They’re also more expensive. A DSLR camera body without lenses costs around $1,000; lenses add a few hundred more.
Still, I’m eager to explore the territory. If you’re interested, read along as I try one or two of the latest DSLR models over the next few months.