Ah, lenses, an alluring mistress that takes all your money, promises much more than it can deliver, makes you feel worried and wonderful at the same time – oh, and broke. I think this is why camera owners often fall prey to “lens lust”. It’s a universally acknowledged truth – if Jane Austen will allow me the conceit – that a photographer with even a bit of spare cash must be in want of a new lens.
Lenses are measured by two things: a) money and b) focal length and aperture. Hordes of marketers spend sleepless nights thinking up new ways of convincing you that (a) doesn’t matter, but (b) does. We’ll deal with (b) first.
For most cameras, lenses’ focal lengths are rated according to a fiction: what it would like on a full-frame (24 x 36 mm sensor) camera. The only problem is that few of us have a full-frame camera. But the only real measurement, the angle of view, is rather hard to comprehend. Different focal lengths narrow / widen the angle of view. A fisheye lens has the widest angle of view (which means you often capture your feet in the image – or at least, I do). A telephoto narrows it. The longer the focal length, the more it flattens the image. This is one reason why portrait lenses are in the 70-150-mm range. As a general rule, the longer the focal length, the longer the maximum focusing distance (i.e., how close you can get to the subject).
The next rating is the lens’ maximum aperture. When you see, for example, a lens rated at 28-300 mm, it means its focal length ranges between 28 and 300 mm. The next bit is just as, if not more, interesting: f/3.5-f/5.6. It means that the maximum aperture at the short end of the lens is f/3.5 (not brilliant, but OK) and maximum aperture at the long end is f/5.6 (distinctly dark). Of course, you can narrow the aperture to f/8, f/11, f/16 at any time, but you can’t expect a lot of light to come in at 300 mm. This becomes important when shooting wildlife and sports at the long end, where you want as much light as possible so that you can reduce the exposure time and keep the ISO down to a minimum.
(By the way, if you want a 300 mm focal length at f/2.8, prepare to spend at least $4000 - just to give you a sense of proportion.)
There are still some lenses that do not offer a zoom feature; the focal length is fixed. These tend to offer better image quality, faster apertures and a higher bill. It’s worth mentioning that Pentax and Zuiko specialise in these, although you’ll find all the big names offering these “prime” lenses. In return for the advantages, you get the draw back of losing the versatility of zoom lenses.
The ream of letters added by all camera manufacturers (Tamron is a particularly egregious example) stands for various things they do. Here are some of the main features:
- USM / HSM: this is a technology used on more expensive lenses to make autofocus faster and more silent. It also offers the possibility of manual focus override (use the AF and then correct). With some exceptions, cheaper third-party lenses don’t feature this option
- IF (internal focusing): the camera barrel doesn’t/shouldn’t extend when focusing.
- ASPH / ED / L, etc.: this has to do with the type of glass / coating used to prevent distortion / chromatic aberration. Sounds good, basically means little to the beginner except in the price tag. With that said, when a manufacturer offers two models of the same lens, an old, discontinued one and a new one with the gizmos, it’s usually worth buying the new one
IS: image stabilization, which is also known as vibration compensation / reduction, etc. Always costs extra and is usually better. Note, however, that image stabilisation compensates for camera shake, not for subject motion blur. You might not need a tripod, but your fast-moving subject remains blurry. Just so you know.
The important point is that if something is too good to be true, it invariably is. Look at all the features of a lens, not just its focal length, and read the reviews on the web.
Lenses are usually sold in two types: beginner / amateur models and models for enthusiasts / professionals. The most obvious difference is in the quality of the model. Professional models tend to be sturdier, more versatile (wider aperture) and offer better image quality. Oh, and they’re far more expensive, of course. Lenses intended for the beginner / amateur market are cheaper, but the price advantage comes at a cost.
Does the cost matter? In many ways, not really. Canon, for example, makes you buy the lens hoods and bags afterwards, but one of its best lenses is dirt cheap: the 50 mm f/1.4. Manufacturers add features (which are expensive) to deal with extreme situations, such as bright light, flare, low light, etc. In many – but not all – cases, you can work around them either by moving or by correcting in post-processing. If all your photos go on the web, you can be happy with the beginner / amateur models.
I haven’t mentioned lenses designed for APS-C sensors only. These won’t fit full-frame lenses. For example, Canon markets EFS lenses, which won’t fit its higher-end models. Other manufacturers do the same. This is important only if you think you might upgrade later on.
Perceptive readers have noticed that I haven’t explained which lens to buy for which purpose. One reason is that fisheyes can be used for wonderful portraits; macro lenses are excellent portrait lenses too and telephotos can be used for macros (at a pinch).
The question is (almost) moot on a compact. The latest (and most expensive) models offering very luminous f/2.0 lenses are definitely interesting. Note that with compacts and cheaper interchangeable lenses, the maximum aperture quickly narrows as you zoom in. If you bought a “kit” DSLR (i.e., a body with a lens attached), chances are it offers the standard range of 24-105 mm. It may state 15-85 mm on the lens, but that takes account of the multiplier ratio of the crop-sensor on most DSLRs. Without going into details, we still hark back to 24x36 mm film and think that 50 mm with this format most closely equates to what the human eye sees. If you have a crop-sensor body, you should be looking at a 30 mm focal length.
Much of this is techno-babble. I tried to keep it simple for one basic reason: different lenses don’t make you a better photographer; they merely extend your range. They are, however, a lot of fun.
I wanted to give you an example of the flattening effect of a telephoto lens. In this example, as Google Earth measures it, I was 1.79 km kilometres as the crow flies from the Acropolis. The distance between the Acropolis and port of Piraeus seen behind it is over 10 km, i.e., 12 km from where I was - but it doesn't look like it. By the way, the distance between the Acropolis and the knobbly monument to the left, known as the mausoleum of Philopappus of Comagene (where do they get their wonderful names?) is the better part of a kilometer, but they look as if they're on the same plane. This is an example of an effect known as "foreshortening", i.e., the flattening effect of telephoto lens.
About "Biff" notes:
Brenda referred to the last post as "Cliff" notes, something my limited knowledge of American education equates to "crib sheet for getting through Shakespeare 101". I almost like the idea, but I think "Biff" is closer to the mark. Anyone who's seen
Back to the Future will know what I mean.
A note to the more technically proficient:
These notes are kept at an intentionally simple level. Please don’t confuse readers with very valid, but rather complex, additional information. However, feel free to correct / simplify my notes. I will edit accordingly and credit you.