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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.
So far we've mostly been looking at fairly everyday lenses, but there are lots of other optical gizmos that you can attach to your camera to achieve all sorts of effects. You can get strange effects, or stylized effects, or even some practical effects. You're already seen a fisheye lens and how it gives you a very wide and very distorted view of a scene. On the more practical end of the spectrum are macro lenses, which allow you to shoot extreme close-ups of objects. Technically what makes a macro a macro lens is that there is a one-to-one relationship between the size of the object that you're shooting and the size of the image that gets captured.
I'm going to skip all the math bit and we'll just say that when you shoot with a macro lens you can shoot close-ups and get perspectives that you just can't shoot with non-macro lenses. Like other lenses macro lenses come in a variety of focal lengths. This is a 100mm macro, but you might also see 60 and 50 millimeter macro lenses. Those shorter macro lenses are lighter and they're less expensive, but they require you to get much closer to your subject than a nice long macro like this 100 millimeter. So if you're serious about macro photography you want to get the longest macro lens that you can afford just for the sake of shooting flexibility.
Now there are some zoom lenses out there that claim to have a macro feature built-in, but be very careful when considering these lenses. If they can't achieve a one-to-one magnification level then they're not true macro lenses. Extension tubes are another budget macro alternative. An extension tube doesn't actually have any glass of. It sits between your camera and your lens and it serves to get the sensor farther from the lens. So it just attaches to the back the way a lens would. Different manufacturers make different sized tubes and extension tubes will only be compatible with lenses up to a certain focal length.
Extension tubes usually won't get you to a full one-to-one macro capability, but they will come close and they're not as expensive as a macro lens. Now the downside to extension tubes is that you have to get closer to your subject than you would with a macro lens and sometimes you can't actually get close enough to focus. Some people confuse extension tubes with a tele-extender or teleconverter like this one, but they're very different. A tele-extender increases the focal length of the lens and it's an actual optical device.
You can see here that there is actual glass in the extender. There is a little lens element in there. This particular extender is a 2x. It doubles the focal length of any lens I put it on. So if I put it on my 400mm lens here, then I have an 800mm lens. As you can see tele-extenders, sometimes called teleconverters, are very light and they're very reasonably priced. So you might think why would I buy an expensive 400mm lens rather than a 200mm lens and a tele-extender? Well depending on your needs that might not be a bad idea, but you should know that there is no such thing as a free extra 200 millimeters.
Teleconverters cost you some light. In the case of this 2x converter, it's a whopping two stops of light. So where this 400mm lens is normally an F5.6, with this converter it becomes an F11. You'll also take a quality hit with a converter. It's basically a magnifying glass that you're sticking on the back of the lens. So while it magnifies the size of the image it also magnifies any flaws or aberrations. You'll definitely notice a sharpness penalty with the converter. Depending on the lens you're using, you may lose autofocus capabilities or your autofocus maybe greatly slowed.
Here is another teleconverter. Rather than 2x it only gives you 1.4x on your focal length, but it also only costs you one stop. So you can eek out a little more focal length without slowing the lens down too much. This is a tilt-shift lens. Now, the way this works is as I turn these knobs, I can move the front and rear elements of the lens independently. Tilt-shift lenses have a number of uses, but they're most commonly used for architectural photography.
Look at this building. Because I was looking up at it from ground level I'm getting perspective distortion. It's no longer kind of perfectly squared off. It's receding into the sky. With a tilt-shift lens, I can correct for that perspective to square up the building. Here is another a fairly unusual thing you can put on your lens. This is a lensbaby and it may look like some kind of orthopedic device of some kind, but what it actually is, is there is a lens element back here and there is another one up here and there is a bellows in the middle and I can turn these kind of torturous looking thumbscrew things and that will shift the bellows so that I now have a crooked lens.
What this lets me do is pick a point of focus somewhere in my image and then smear everything in the image out from that point of focus, as you can see in this image. Those are just a few of the options that you might find for your camera. There are other things you can stick on the front of your camera such as a pinhole lens for shooting digital pinhole photographs, Holga lenses for getting a grungy toy look, telescope adapters for sticking your camera on the end of a telescope, and a lot of other things. If you're interested in a particular type of photography, a little Googling around should lead you to resources and product reviews on specific hardware.
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