What You Should Know About Lenses :: Digital Photo Secrets

What You Should Know About Lenses

by David Peterson 3 comments

Before you bought a DSLR you didn't really need to know a whole lot about lenses. Your point-and-shoot camera came with a lens already attached, and there really wasn't anything you could do to change it. You probably knew how much zoom it had, and if you paid attention to the specs you may have also figured out what that meant in millimeters. But if your knowledge didn't really go any further than that, well, no one can blame you.

Now that you have a DSLR, though, it's a lot more important to know something about not only the lens that you bought with it, but the other lenses that are available to buy once you decide it's time to expand your arsenal.

Now as it turns out, there's a lot to know about lenses. A lot. It's not just a matter of wide-angle vs. telephoto, there are a lot of other things to take into consideration as well. But let's start with the basic stuff, and that's lens classes.

Normal lenses

So-called "normal lenses" don't have that name because it's any comment on you personally, or your quirks as a photographer. A "normal lens" is simply a lens that will reproduce objects at roughly the same size that they appear in real life. When you look through a normal lens, the scene you see is going to look pretty much the same as the scene you see when you look away from the viewfinder. For the most part, this means 50mm.

Standard zoom lenses

This is a lens that gives you a basic focal length range. A standard zoom can either be wide angle or short telephoto. Lots of "kit lenses," or those lenses that are sold as a bundle with camera bodies, will fall into this range. An 18-55mm lens is an example of a wide angle version, a 28-135mm lens is a short telephoto. The reason why these lenses are the ones that get bundled with a new camera is because they're useful for most of the activities that the average consumer is going to use them for, such as landscapes, travel photos, family snapshots etc. These lenses give the average person the flexibility to shoot in a lot of different situations.

  • Canon EOS 450D
  • 200
  • f/1.8
  • 0.001 sec (1/1600)
  • 50 mm

Untitled by Flickr user Chiara Cremaschi

Wide-Angle lenses

Wide angle lenses have shorter focal lengths than that 50mm "normal" lens does. When you use a wide angle lens, you can get a lot of the scene into a single image, while normal and telephoto lenses will limit you to only part of the scene. But it's not just a matter of being able to capture those big, sweeping landscapes—wide angle lens also exaggerate size and distance. For example, you can place a person in the foreground of your image and make it look like she's a lot larger than she actually is, and you can also exaggerate the distance between her and whatever happens to be behind her. Wide angle lenses are also great for shooting interiors—when you use a normal lens, you can't step back far enough to get the whole room into the shot without some wall or another getting in your way.

Any lens in the 12 to 24 mm range is a wide angle. A fisheye lens is a wide angle, too, but it belongs in a different class than the other lenses we've been discussing here. Wide angle lenses record straight lines as straight, while fisheye lenses will turn straight lines into curved ones, causing some weird distortion in your images.

  • SLT-A77V
  • f/9.0
  • 20 mm

pokhara lake and boats by Flickr user mariusz kluzniak

Telephoto lenses

Telephoto lenses have long focal lengths, from a low of 70mm all the way up to 600mm. They're generally used for shooting sporting events, wildlife and other subjects that you can't really get close to with your feet. You can get telephotos that zoom (more common for the consumer market) or you can get them in fixed focal lengths. The primary differences between them (apart from the quality of the glass) is in aperture. Expensive telephoto lenses will let you shoot at much larger apertures (Canon has a fixed focal length 500mm lens with a maximum aperture of f/4, compared to Sigma's 150-500mm zoom, which will only go as wide as f/6.3. The difference between the two is about $8,700.) Just to confuse the matter even more, most inexpensive telephoto zooms have variable apertures. For example, a 70mm to 300mm zoom may let you shoot at f/4 on the short end, but no greater than f/5.6 on the long end. This is generally only a problem in low light, but it is something you should be aware of when shopping. Of course, fixed aperture lenses are more expensive than variable aperture lenses—usually significantly more expensive.

Another thing you should keep in mind when shopping for a telephoto lens is that the longer the lens is, the faster your shutter speed will need to be, otherwise you'll get visible camera shake in your photos. If you are going to be shooting in low light, look for a lens that has image stability built into it. This usually gives you a few stops of leeway in terms of shutter speed—which means you can go a lot slower with your shutter speed than you'd be able to if your lens didn't have that feature.

  • Nikon D50
  • 200
  • f/0.0
  • 0.001 sec (1/1000)
  • 5.0 mm

Reflections 2 by Flickr user carvaka

Super Zooms

Super zooms are sort of a hybrid between a wide angle zoom and a telephoto zoom. A typical super zoom lens will give you a range of 18 to 200mm, even 300mm for some models. These lenses are great for traveling, especially if you don't want to be lugging a bunch of lenses around with you wherever you go. Unfortunately they also don't produce awesome pictures when compared to their less-super counterparts. Photos taken with super zoom lenses aren't as sharp as those that come from standard zooms.

Prime vs. Zoom

There's another distinction you may have heard about, and that's the distinction between a prime lens and a zoom lens. The difference is really very simple—zooms zoom, and prime lenses don't. A 50mm lens is a prime lens, and a 24mm to 70mm lens is a zoom lens. There are some advantages to primes over zooms, and vice versa—prime lenses are typically faster than zoom lenses, which means for example that you can get a 50mm prime lens with a maximum aperture of f/1.4, while that 24mm to 70mm lens might only go as wide as f/2.8. Another advantage is that prime lenses tend to be cheaper and lighter than zooms, but the most often-cited reason to prefer them is because they often take sharper, better-quality images. Now this is changing as time goes on, and there are certainly zooms on the market that can rival prime lenses in terms of picture quality. And there are certainly reasons to prefer zooms over prime lenses, with the most obvious being convenience. You can carry one zoom lens around with you and accomplish most of what you need to, usually without having to move your feet. If you're using only primes, you either need to carry around a series of them (and then spend an endless amount of time swapping them out), or you need to do an awful lot of hiking to get as close to your subject as you'd be able to do if you had a zoom lens.

Crop factor

This is something you should pay attention to, to a certain degree, because it has a lot to do with how a lens is going to work on your camera. "Crop factor" refers to the size of your camera's sensor. A "full frame" camera, for example, has a sensor that takes images that are roughly equivalent to the ones you'd get if you were using an old 35mm camera. Other cameras are "APS-C" or "DX," which are two different names for the same thing—a camera that has a smaller image sensor than those full frame cameras do. This is called a "crop sensor," because what it means is that if you put a 50mm lens on the full frame camera you'll get more of the scene into the shot than you will if you put the same lens on an APS-C camera. In a sense, you'll get a "cropped" photo on that APS-C camera, hence the name.

Crop factor only really starts to matter when you’re using, for example, a lens designed for an APS-C camera with a full frame camera. As long as you’re purchasing lenses that were made to fit your camera body, this really isn’t going to be a concern for you.

Aperture

Another thing that you need to be very aware of any time you go lens shopping is aperture. You already know what aperture does for your photographs, but it’s good to know exactly what’s going on behind the scenes when you shoot with a small or large aperture. The term “aperture” refers to the size of the diaphragm inside your lens, which is the hole that allows light to reach your camera’s sensor. As you change your f-stop, this hole becomes larger or smaller, thus allowing more or less light to reach the sensor. Larger apertures (represented by smaller f-numbers) allow more light to reach your camera’s sensor, allowing you to shoot in lower light conditions without having to sacrifice shutter speed. Those larger apertures also produce images with less depth of field, or a smaller distance between the things that are in focus and the things that are out of focus.

Again, all lenses are not created equal when it comes to maximum available aperture. While most of them will give you fairly small apertures, those larger ones can be elusive, especially on budget lenses or lenses with long focal lengths. That 50mm prime lens, for example, can have a maximum aperture of f/1.8 or even f/1.4, but a 300mm lens might not be able to go any wider than f/4. And again, zooms will often have a variable aperture, such as f/4.5 at the wide end and f/5.6 at the long end. What this means for you is less flexibility—but it also means a pretty big cost savings for you, pocketbook-wise. Larger aperture lenses are more expensive to manufacture, so their price tags tend to be quite high compared even to lenses in that sort of mid-price range.

Quality issues

Photography is an expensive hobby, even when you’re not paying top-dollar for every piece of equipment you own. If most of your arsenal consists of budget lenses, with a few of the higher priced lenses mixed in for good measure, you’re probably like the majority of other hobbyists out there. I would never suggest that you should mortgage your house or spend your kids’ college funds so you can buy a high quality lens, but you do need to understand some of the shortcomings of that budget gear, so you can work within the parameters of the lenses you do own. So to finish up this discussion, here’s the short list of some of the problems you might notice with those less expensive lenses.

1. Soft focus.

A less-expensive lens isn’t going to be as sharp as a high quality lens. For most hobbyists, this doesn’t matter a whole lot because most hobbyists don’t tend to print photos at large sizes (image softness is much more obvious the larger the print size is). But when you look at your photos at 100 percent, you may notice softening of the details, especially as you get closer to the corners of the image. If this is something that concerns you, you may want to think about saving for a more expensive lens, but remember that unless you’re shooting for photography competitions or you frequently order prints in large sizes, it’s unlikely anyone will ever notice the difference in sharpness between your budget lens and one of those very expensive, professional-quality lenses.

2. Contrast.

Lens contrast (as opposed to tonal contrast), refers to a lens’s ability to distinguish between very small details that have the same or similar tonal value. If a lens has good contrast, you will be able to see the boundaries between those very small details, even if the tones present in each detail are very close to being the same. Less expensive lenses aren’t as good at this, which means that fine details may be lost. Again, you have to ask yourself how noticeable this is, and how much the difference actually bothers you.

3. Distortion.

Images shot on budget lenses tend to be less accurate in terms of the shape of the object that's being photographed. You will notice this effect more in subjects that have a lot of horizontal and vertical lines, especially flat surfaces like brick walls. There are two types of distortion: barrel and pincushion. In barrel distortion, the image looks a bit like it has been wrapped around a barrel—hence the name. This is generally a problem with wide-angle lenses. Pincushion distortion is the opposite of barrel distortion—instead of appearing to be wrapped around a spherical or barrel-shaped object, an image that has pincushion distortion looks as if it's being squished in the middle into a sort of hourglass shape. In pincushion distortion, the magnification is greater the further you get from the optical axis, resulting in that pincushion shape. Pincushion distortion is a problem of telephoto lenses.

Both these distortion problems increase or decrease as you change focal length—barrel distortion gets worse the wider you go, pincushion distortion gets worse the longer you go. Now this can be annoying, but the good news is that you can correct most distortion in post processing, so this alone may not be reason enough for you to upgrade to that very-expensive lens.


    Vandalism by Flickr user Voxphoto

    4. Chromatic aberration.

    This is a phenomenon you may have noticed in areas of high contrast, especially with your more budget-friendly lenses. Also called “purple fringing,” chromatic aberration is a thin band or smear of color that appears along the borders between very dark areas of your photo and very bright ones (contrary to the name, it doesn’t always have to be purple in color). The reason this happens is because of the quality of the glass itself—manufacturers use a low-dispersion glass in those higher end lenses, which reduces the potential for chromatic aberration. So again, this problem is typically seen in lower-priced lenses. But it’s also one that can be corrected in post processing, so you need to decide for yourself if it’s worth the effort to correct or if you’re better off saving for a more expensive lens.

    • Nikon D90
    • 400
    • f/5.6
    • 0.002 sec (1/640)
    • 300 mm

    Hello there! by Flickr user chris jd

    5. Vignetting.

    A final thing to watch out for is vignetting, which is a darkening of the image in the corners. This is typically a problem with wide angle lenses, and it also tends to be more pronounced the wider you go. Vignetting is sort of a personal thing—some of us find it annoying because it mucks up the details in those corners, while others think it adds an artistic quality.

    Conclusion

    I know that was a long primer, but I feel like lenses are less well-understood than they ought to be, especially among beginners. Understanding what your choices are in the lens marketplace is going to make you a more savvy shopper, but also a better photographer. To make the best use of your equipment, it’s always good to have a strong understanding of that equipment. So keep this article on hand and refer to it the next time you think you might want to upgrade your lens. I hope it will give you the information you need to make an educated choice.

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    Comments

    1. Eva says:

      Thank you David. I learnt a lot from this article.

    2. john says:

      Saying that "Other cameras are APS-C or DX, which are two different names for the same thinga camera that has a smaller image sensor than those full frame cameras do." is making mess in peoples heads. APS-C is not just a smaller sensor camera, it's a camera with exactly 1.5 (1.6 in case of Canon) crop factor. Micro 4/3 system cameras also have a smaller sensor but they are not APS-C.

    3. Derek Stubbs says:

      Most useful as always thanks David.

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