Monday, November 23, 2009
Hello everyone. I apologize for not putting up a post on Friday – I was sick and sleeping it off. I’m back in action today though, although I’ll be out of town the rest of the week after tomorrow, so this post and the next one will have to keep you satisfied until next week.
Today’s picture was taken along the Baker Lake trail, which can be accessed by heading off 20 or 30 miles on a forest road shooting north from Highway 20, the road that goes through North Cascades National Park. It’s a beautiful area, even if you don’t leave the car.
If you’ve been shopping for cameras or lenses any time in the last couple years, you’ve probably heard the term “Image stabilization” (or some variant on the theme – different manufacturers call it different things.) So.. what exactly does it mean, and what does it do for you? And, the million-dollar question that I’m not going to answer, is it worth the cost?
The basic problem that image stabilization is trying to solve is that taking pictures in low-light is hard. In bright light, you can get away with using whatever size of aperture you like and a low ISO, and you won’t have any problems. And by “you won’t have any problems” I mean “you’ll be able to use a shutter speed that’s fast enough that you won’t get any blurring from camera shake.” Humans have shaky hands. It’s a fact of life. So if your shutter stays open too long, your camera will move, and the resulting picture you take will be blurry. Tripods are one solution, but what if you don’t have one? That’s where image stabilization is. It’s technology in the camera or lens that compensates for your shaky hands to keep the light reaching the camera sensor steady. A lot of the time that means having a spinning lens element that acts sort of like a gyroscope. The spinning element likes to maintain it’s angular momentum, or something (I really have no idea what I’m talking about here, could you tell?), such that the beam of light passing out the back end doesn’t change despite the fact that the lens moved. Even re-reading that sentence it still doesn’t make any sense. But whatever, you get the idea.
The basic rule of thumb is that, if you’ve got image stabilization, you’ll be able to take hand-held pictures one or two stops slower than you would otherwise. Wait, what? Okay, I’ll take a step back. You of course want each picture to be “properly exposed” -which means “exposed the way you like it”, there isn’t a scientific definition for proper exposure. Basically, it means “not over-exposed (too light) or under-exposed (too dark”). There are lots of factors that go in to how much light reaches the camera’s sensor (or film) to reach a certain level of exposure. Keeping most of them constant for now, we’ll just talk about the shutter speed and the aperture (or f-stop). In general, those two are inversely proportional. That is, the wider the aperture (the more open the hole), the less time you’ll need to have the shutter open for. And vice versa (a smaller hole means you’ll need more time with the shutter open.) Again, I’m ignoring for the moment all of the side-effects from changing your aperture or shutter speed (like depth-of-field, blah blah blah), I’m strictly dealing with exposure level right now – how light or dark the resulting image is. As I mentioned before, in bright light, you can make the aperture as small as you like without having to worry about needing a shutter speed longer than that magic amount of time where hand-shake becomes a factor. In low light? Not so much. If you’re in, for example, a shady forest, you may not be able to use the aperture size you want – it would require that you keep the shutter open too long to be able to hold the camera steady. A good rule of thumb (for me anyway) is that any shutter speed faster than 1/200th of a second means I’m good to go. Sometimes I can push it to 1/100th of a second or even slower and still be happy with the result, but anything slower than 1/200th means hand shake could start to become an issue. That’s without image stabilization. WITH stabilization, you can move that down a bit, meaning that I can be pretty confident that anything faster than 1/160th of a second or even 1/125th of a second will work out fine, and the grey area moves too, down to about 1/50th of a second or so. To go back to how I started this paragraph, that means I can close down the aperture one or two (f) stops, and even with the corresponding increase in required shutter time, I should be okay.
So, awesome, right? Well, yeah, kinda. There is of course always a downside, which is usually the cost. Lenses with image stabilization can cost a LOT more than a similar lens without it. The cost is of course coming down as it becomes more and more popular, but the general rule of thumb still holds true. For point and shoots, at least for Canons (which are really the only ones I know anything about), I think it’s pretty hard to even find one without it these days. But, despite all of the hooplah about it, it’s not really a HUGE difference, it may get you a picture here or there that you wouldn’t have been able to get otherwise, but it’s definitely not worth refinancing your house to pay for. In fact, many people (myself included) go the route of spending money on getting a “faster lens” (a lens with a larger maximum aperture size – or a lower minimum f-stop) rather than on a slower lens with image stabilization. Image stabilization sometimes means that you’re making tradeoffs in image quality (to keep costs more reasonable) which I decided I was no longer willing to make.
Why did I bring all this up today? As it turns out, this is one of those pictures that I probably wouldn’t have been able to get without it. This was taken with my 28-300 mm super-zoom that I no longer use regularly. I used a shutter speed of 1/50th of a second, which is normally too slow to get a decent image. Even with the stabilization, most pictures I take with that shutter speed won’t turn out. But some of them do. If I had the lenses then that I do now, I cold have of course just opened up the aperture wider and used a faster shutter. There would have been a correspondingly smaller depth-of-field, meaning the trees in the background would have been more out of focus. But it’s tough to say how drastic of a change it would be. If I knew I was going to be put in the same conditions again I’d definitely reach for my 28-75 f/2.8 over my 28-300 f/3.5-6.3 with image stabilization. But again, that’s just personal preference.
Anyway, that’s enough blabber for today. See you all tomorrow!
Notes: Canon EOS Rebel XT, Tamron 28-300 mm VC lens. 1/50s, f/3.5, ISO 400. Focal length: 35mm.