I own a lot of lenses. I'm a bit of a lens addict, and I admit, I get all giddy when a new one comes out. Whenever I travel, I get the eye-roll from my husband when he asks me how many lenses I'm going to take. The best example of this was our trip to Africa, in which I toted around 4 different lenses everywhere I went "just in case." I think I spent more time switching lenses than I did taking pictures. But, there is a reason to the madness... shooting with the right lens can make all the difference in your photos. When it comes to food photography, I use two lenses: a Canon EF 100mm f/2.8 Macro and a Canon EF 50mm f1.4. When I first started buying lenses, all those numbers just sort of ran together, and I really had no clue what they meant. I know a bit more now, so here's a quick tutorial on how to interpret:
Technically, the focal length is the distance between the lens surface and the image sensor (or film) measured in milimeters. The greater this distance, the greater the magnification of what you are shooting. A smaller number gives you a wider-angle, so you end up capturing more of the scene. A larger number magnifies the image, allowing you to fill the frame with a small object from a greater distance. The example above uses my 180mm, 100mm and 50mm respectively all from the same distance, about 4 feet away. Most food photography is fairly close, detailed work, so you rarely need a wide angle lens. I'd recommend sticking within the 50mm to 100mm range.
You may sometimes hear people talking about prime lenses. Prime simply means it's a fixed focal length, and not a zoom lens. Zoom lenses support multiple focal lengths, so with one lens you can zoom in or out to get a range of sizes. Typical zoom configurations are 28-80mm or 100 to 300mm. You will pay more for a zoom lens and it won't be as fast, but it does offer greater flexibility. For food photography zoom is unimportant. It's easy enough to move your camera closer or further from the subject. If you are investing in a general purpose lens for all your photography it may be worth the extra cost.
The camera's aperture is the opening that lets light in, and it gets bigger or smaller depending on the lighting conditions and the desired look of the photo. It's a bit weird, but the lower the number the bigger the opening. So a 2.8 might be "wide open" on your lens. When your lens is wide open, you are able to take photos faster (less shake, sharper pictures) and with a narrower depth of field. I'll talk more about depth of field in another post, but a narrow depth of field basically means that only a small amount of the image is super crisp, and the rest (typically the background) is beautifully blurry... giving the eye a clear sign of what to focus on. In the example above, I shot the left image at f7 and the right image at 1.4. Neither is right or wrong... it's all about what look you are going for. A lens with an aperture that only goes to 5 still might meet your needs, but it will be harder to get this kind of image.
Just about all lens today offer auto-focus. However, for food photography, I've stopped using it completely. The mechanisms for auto-focus when dealing with the lighting conditions and soft shapes of food often get tripped up, and it's just faster and more accurate to manually adjust. I'll talk more about how to manually focus in a later post.
Lenses need a certain distance between the end of the lens and the subject in order to focus. A macro lens simply lets you get really, really close to the subject and still focus. Think an inch instead of a foot. Combine that with a bit of telephoto (100mm or 180mm), and you get just the smallest slice of your subject in great detail. Things look much different from this point of view, and you can bring new life to just about anything. You definitely need a macro if you are shooting food.
There are lots of other specialty lenses available that do all kinds of wacky things... tilt-shift lenses let you keep the camera body perpendicular to the subject and shift the lens up, which is great for correcting perspective of wide angle shots. It's critical if you are shooting a lot of architectural shots, but a lot of pro photographers really like a tilt-shift for food photography as well. I haven't ever shot with one, but I'll rent one sometime in the coming months, and let you know how it turns out. A fisheye is just an ultrawide lens (usually 15mm) that has a characteristic convex appearance that corrects natural distortions you would get with a standard wide lens. Neither of these are needed for food photography, but if you are looking to do something different, you might play around with them. More interesting is the Lens Baby which lets you play with different selective focusing methods and blurs. Check out some of the lens baby photos on flickr... I don't have one yet, but I want one!
Image stabilization (IS on Canons, VR on Nikon) helps dampen vibrations and shake which can lead to blurry photos. This is incredibly helpful when you are shooting with a lens of a higher focal length (200+), and you aren't getting the fastest shutter speeds. If you are using a tripod (and you should be... more on that in a later post), you should turn it off. But, when you are purchasing lenses, it is a nice feature if you can afford it.
Each lens manufacturer uses their own special designators for different classes of lenses and different features that effect scary sounding things like chromatic aberration. For Canon, the EF means electrofocus, and any EF lens should fit any EOS Canon camera. Some newer Canon camera bodies also support EF-S lenses, but make sure yours does before you consider buying one of these lenses. The "L" means luxury as if that helps. It basically means it's their highest class of lenses. You will definitely pay more, but you will also have a lens that you won't quickly outgrow. The rest of the acronyms? You really don't need to worry about them.
Most digital SLRs have a smaller sensor than a 35mm film camera. But, they use the same lenses. The result is that a photo taken with a digital SLR will not show as much of the scene as the same shot taken from the same lens and distance as a film camera. It's slightly cropped or more zoomed in, depending on if you are a half-full or half-empty kind of person. This really won't affect your shooting much, as you can generally make up the difference simply by moving further away from your subject and what you see in the view finder is still what you get. So, unless you do a lot of switching back and forth between film and digital, you'd probably never notice. While there is a lot of talk about new digital lenses that are more suited to the sensors in digital SLRs, the primary difference is that they "correct" for this discrepancy and make the lenses a bit wider. There's really no need to upgrade to these digital lenses if you are happy with the image quality of lenses you already own. On the Canon side of the house, I whole-heartedly recommend both of the lens I use - the 50mm 1.4 and the 100mm 2.8 macro. The macro is a bit soft but that works well for most macro work. I actually prefer it to the 180mm 2.0L, which technically is a better lens. I'm less familiar with Nikon lenses, but this site offers in depth reviews of Nikkor lenses. If you are on a budget, try looking for used lenses. However, don't buy one unless they offer a reasonable return policy. A good test to look for flaws (after it has been cleaned) is to shoot a solid color, usually white or grey and look for any abnormalities. The other main thing to look for with used lenses is how smoothly the focus rings and aperture rings turn. A sticky ring will drive you nuts and may be hard to fix.