Adventures in Digital Photography With Linux, part 5: Aperture, Shutter Speeds, and ISO
Welcome back! In part 4 we ranged all over the place, from how to manage and edit your photo archives with Linux, some discussion on choosing lenses, and finally getting down to the most important part of getting high-quality photographs: understanding aperture, shutter speeds, and ISO. Part 4 covered the fundamentals of aperture, so let's leap in to shutter speeds and ISO. This applies to point-and-shoot cameras as well as the fancy DSLRs with herds of different lenses; if you don't understand these three photography fundamentals, you won't understand how to get the best photos.
Shutter SpeedsThis is pretty simple: the faster the shutter speed, the better you can stop movement. But of course there is a tradeoff- faster shutter speeds require brighter light. No problem, because all you do is increase your aperture, right? Yes and no, because aperture also affects sharpness. Wider aperture = shallower depth of field, which means that parts of your picture might be out of focus.
If your camera doesn't let you make manual settings, chances are it provides you with a range of shooting modes like macro, portrait, sports, beach, landscape, night portrait or campfire, and so forth.
Macro and portrait are both aperture-priority at a wide aperture to blur out the background.
Sports is shutter-priority and sets the fastest possible shutter speed.
The beach setting uses spot-metering to compensate for a bright background, so this is a good setting for any strongly backlit subject.
Landscape is aperture-priority using a small aperture.
Night portrait or campfire, depending on what your particular brand of camera calls it, combines the flash with a slow shutter speed. So the flash illuminates your subject, and the slow shutter speed captures more details in a dark background.
Image StabilizationMost digital cameras come with image stabilization (IS). IS is a wonderful thing to have, as long you understand its limitations. It compensates for camera movement, but not subject movement. So it won't help stop a fast-moving subject. But it will gain you an F-stop or two under dim lighting conditions with slow-moving and stationary subjects.
It won't help you with careless shooting technique, either. You still need to hold your camera as still as possible and press the shutter button without jerking it. The longer your lens, the more camera movement is magnified.
ISOOldtimers remember the days of ASA film speeds, which were later replaced by ISO numbering. ISO works exactly the same way with both film cameras and digital cameras: lower number = lower sensitivity, which paradoxically = higher image quality. Film emulsions are made with silver halide, which has grains. Smaller grains make higher-quality images, but have lower light sensitivity so they require longer exposures. Faster films have higher sensitivity because the silver halide grains are larger, which you can see in photographs. Professional photographers use films with ISO speeds as low as 6. Consumer-grade films start at ISO 100. I used mainly Fujicolor 400-speed film because it was fast enough for all occasions, had wonderful color saturation, and it was not noticeably grainy in prints up to 5"x7".
Digital camera sensors have the same set of trade-offs: higher sensitivity means shorter exposures, but also more noise. (Scroll down this page to see what digital camera noise looks like. You can easily replicate these tests with your own camera.) But digital cameras have two big advantages over film cameras- higher-end cameras let you change the ISO anytime. You're not limited by the film anymore. And camera sensor noise can be mitigated by software, both in the camera and in post-processing.
Life Without FlashNo, not Macromedia Flash, but camera flash. When you're in low-light conditions and don't want to use a flash, just kick the ISO up a few notches until you get a decent shutter speed. Some cameras handle noise reduction better than others, so it will take some experimentation to find out what is acceptable for you. You can fix anything in post-production, depending on your skill and software, but my goal is to make the camera to do as much of the work as possible, and get the best possible image from the start.
Digital Zoom vs. Optical ZoomDon't be suckered by claims of gazillion-X digital zoom. Digital zoom is nice for when there is no other way to get the picture, but it's death on image quality because it's just magnified pixels. If you need a long zoom range, go for maximum optical zoom. 10x and 12x are common, and when you add a bit of digital zoom you have the equivalent of a backpack full of lenses in one camera. My favorites are the Panasonic Lumix cameras. These come with first-class Leica optics, rechargeable batteries, compact size, and are first-class performers. Canon, Nikon, Olympus, Fuji, and Kodak all make excellent point-and-shoot digital cameras.
Camera Storage CardsDon't go cheapskate on your storage cards, whether they're SD or Compact Flash or something else. Go with the top brands like SanDisk, Kingston, and Lexar. You'll also have a choice of transfer speeds; there are slower cards and faster cards. A lot of cameras, especially the point-and-shoots, are slow enough that a faster card makes no difference. But if your camera does support fast shooting get the fastest cards you can.
Putting It All TogetherSo now you know my master plan for being happy with F/4 lenses, rather than faster (and bulkier, heavier, and more expensive) lenses: with canny use of IS and ISO manipulation, I gain enough stops to get good images in low light. Of course there is a limit, and then either a tripod or a flash are necessary. But for the type of photography I like to do- handheld candid shots- it works out well.
While we're on the subject of tripods, one of the best values of all time is the Slik Pro 700DX tripod and 3-way pan head combination. It costs around $129 and outperforms snooty outfits costing three times as much. It handles beautifully, sets up fast, is extremely stable, and it's easy to make finicky adjustments. It's a on the heavy side, weighing in around 8 pounds, and it supports 15 pounds with ease. Which is more than most people need, but if you don't plan to lug it around on hikes and such, it's a great value. I use it for astrophotography, loading it down with a telescope-and-camera, as well as just the camera, and it handles them better than any other tripod I've tried.
Speaking of flash photography, before you decide to hate the flash that's built-in to your camera, check the settings to see if you can change its intensity. Another slick trick is cover it with a bit of ordinary gauze to soften it.
Hopefully you are now equipped with enough knowledge to select a camera with a useful feature set and to get the most out of it. The current generation of digital cameras give a huge amount of value for their cost. Stay tuned for future installments, in which we will have fun making prints and Web galleries and all kinds of stuff, using only genuine Linux software.
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