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Many of the creative options available to a photographer hinge on an in-depth understanding of lenses. In Foundations of Photography: Lenses, Ben Long shows how to choose lenses and take full advantage of their creative options. The course covers fundamental concepts that apply to any camera, such as focal length and camera position, and shows how to evaluate and shop for DSLR lenses. The second half of the course focuses on shooting techniques: controlling autofocus, working with different focal lengths, and managing distortion and flare. The course also examines various filters and contains tips on cleaning and maintaining lenses.
When you shoot telephoto, whether you're shooting sports or shooting nature or just spying on your neighbors, you're capturing a very narrow crop of the world. One of the tricky things about shooting extreme telephoto is that when you take that very narrow crop of the world, it's very easy to see when that crop is moving around. That can make it very difficult to frame. It's hard to really get zeroed in on the bit that you want. Well, what's more, as you learned in the Foundations of Photography Exposure course, it can require a much shorter shutter speed when you're shooting at extreme telephoto. As you'll recall, the handheld shutter speed rule says that your shutter speed when shooting handheld should never drop below 1 over your focal length. So I have here a 70-200 millimeter zoom lens and right now I'm putting it on a focal length of 100. According to the handheld shutter speed rule that means my shutter speed should not go below 1/100th of a second. If it does, I'm going to risk camera shake, which is going to blur my image. Now if you're using a camera that has a crop factor, if you're using a camera that has say like a Canon camera that has a 1.6x multiplier or a Nikon camera that has a 1.5. Let's say I'm shooting with a 1.6. This lens at this focal length is actually a 160 millimeter lens. That means that my shutter speed should not go below 1/160th of a second or I'll be risking handheld shake. Now fortunately these days there's an amazing technology called optical image stabilization. The way optical image stabilization works is, as you've already learned a lens, a camera lens is actually composed of a bunch of different lenses, some of them cemented together into groups. The last one over here is built in a way so that it can change its shape or move around so that as I jitter the lens this way, it can change its shape to bounce the light back in the same amount the opposite direction to even out shake. Now, this is not a substitute for a tripod. I'm not going to be able to even out riding in the back of a jeep or something. But as far as just evening out the kind of handheld shake that you get just from being alive, it can take care of that and really smooth out your images. So this is a 75-300 millimeter lens that has a stabilizer and I know that because there is this big stabilizer switch right here. I can turn the stabilization on and off. Stabilizers are rated in terms of stops. So let's say for example that the manufacturer claims four stops of stabilization on this lens. That means that if I'm shooting at a focal length of 100, when I'm calculating my handheld shutter speed rule, I can go down four whole stops to find out what my minimum shutter speed is for shooting handheld. So a stop is to-- going down a stop means to halve. So 100 divided by 2 would be 50. That's one stop. 1/25th would be two stops, a 12th would be three stops, a 6th would be four stops. That means I could go down to a 6th of a second and still shoot handheld. Let's assume that 4th stop is more of a marketing claim and that it only kind of works on a test bench and go back to 3 stops. So I could shoot probably pretty safely at a 12th of a second. Now at that speed, things that are moving around in my frame, they are still going to be blurry, but I'm not going to have handheld shake. This is a fairly simple stabilization mechanism. Also, Nikon shooters know that Nikon calls this technology vibration reduction. So you'll see VR lenses rather than IS lenses. those are the lenses that have stabilization and like the Canon stabilization, Nikon stabilization is excellent. Here's a lens with a more complex stabilizer. So I've still got my stabilizer on/off switch here for turning stabilization completely off if I want, but I also have the Stabilizer Mode. So when I'm in Mode 1, the lens is completely stabilized. It stabilizes any little bit of shake that I do to it. When I switch to Mode 2, it only stabilizes one axis. The point here is that when I pan, my pan is kept stable on the vertical axis, but there's no stabilization applied to the horizontal axis. I don't want to trying to even out movements that I'm making this way, because I'm actually trying to move the lens that way. I am going to show you another switch on this lens that-- We're going to come back to stabilization in a second. This is about focus. This lens is interesting, because it's got these two different focus modes. This switch says 2.5 meters to infinity and over here I've got 1.4 meters to infinity. This allows me to kind of optimize the auto focus on this lens. Because this is a long lens, there are going to be times where I'm probably only worried about shooting things and focusing things that are really far away. So if I know that I'm not going to be shooting any closer than 2.5 meters, you can flip the switch over to 2.5 meters to infinity and that will make you auto focus faster, because it won't bother searching in that closer range. That's going to give me a slightly faster auto focus mechanism. Here is another example that's kind of cool. This is a macro lens. So there are times where I'm going to be shooting really close with it. It's actually got three switches. I can tell it Full, which means "Oh, mighty lens, when you're searching for auto focus, search through the entire range of focus" or go down to only searching for half-a-meter to infinity or if I know that I'm going to be just working really close up, which I tend to do a lot with a macro lens, only look for focus between 0.3 and 0.5 meters. So this is a way of really refining my focus. It's never even going to try to focus on infinity, which will save me a lot of hassle with the lens isn't suddenly going to go way out of focus, and notice that this also has a stabilizer, which is very important, because when you're shooting macro, you're in really close and you don't want it? you want the camera? you want the lens stabilized. That's why there's a stabilizer. So one of the most important things to know about stabilization as you've already seen is that I can turn it off, because stabilizing takes battery. When you put the stabilizer on your camera or when you put the lens on your camera, the first time you press that shutter button, you'll probably really notice that when you half press, the lens starts doing something. There's a little kind of whir sound as it starts stabilizing and you should see the image in the viewfinder sharpen up. Some point and shoot cameras have optical image stabilization and it's the same technology that's in a big lens like this. But point and shoot cameras also often have digital stabilization and that's where it takes the frame and actually tries to just digitally crop the frame and move it around to keep it stable. You don't want digital stabilization. It can very much degrade your image and it doesn't work nearly as well as optical image stabilization. Fortunately a lot of vendors have abandoned that. If you do have it, there is a way to turn it off and you should do that. Some camera vendors issue lens stabilization and instead stabilize the sensor. The sensor itself can move around to compensate for movement. Olympus cameras use this. Sony SLRs use image stabilization or image sensor stabilization. What's nice about that is any lens that you put on the camera ends up stabilized. What can be a downside to sensor- based stabilization is in some cameras you don't see the effects of the stabilization in the viewfinder, so you don't get the advantage of having ease of framing. Because the stabilization is basically downstream of the viewfinder. So when you're hunting for a lens, you want to pay attention to stabilization. It's a great feature to have and stabilization technology from pretty much every vendor these days is so great. It's really worth investing that little bit of extra money, particularly when you're working on the telephoto end. This is my 24-105 millimeter lens. It's my walk-around lens. And look, it's even stabilized, which is great, because even at 105 millimeters there is a time that I could, times when I could suffer from camera shake. If you're looking for a wide angle lens, you're not going to find one that's stabilized because there's simply no need. When you're framed out really wide, you're just not going to notice if there's a lot of camera shake. So if you've been hunting for a 16-35 say that's stabilized, you're probably not going to find it. But notice that stabilization is not just for giant lenses. Even a walk-around lens can benefit from it. So check your camera's manual to learn the details of your particular lens' stabilization or your camera's stabilization feature if your sensor is stabilized.
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