Getting started with serious digital photography Part 2: Buying DSLR Camera Lenses

In the first part we decided what type of camera to buy. While not a foregone conclusion for the rest of this guide I will assume you chose to go with a DSLR camera. The next item you need to think about with a DSLR is lenses.

One of the main attractions of a DSLR is the interchangeable lenses. This feature makes it so much more versatile allowing you to work with completely different types of photographic situation from extreme close-up to distant action shots such as sports. It does though at times have enough variables to give the best of us a headache.

[While reading this section while I will explain as we go you might want to refer to the Camera Lens Glossary and Jargon Guide]

Lens Focal Lengths

Lenses come in different focal lengths written in Xmm which is roughly speaking a measurement between the lens and the film/sensor. At the smallest millimetres end are “fisheye” and wide which fit more of the scene into frame and at the extreme show bulging, distorted, exaggerated images. Wide angle lenses are favoured by many landscape photographers because you fit so much scenery into one picture. At the other extreme is telephoto which will fit less of the scene into frame but at greater magnification. In the middle is “normal” which is a field of view roughly comparable what you see with your own eyes and often considered 50mm or thereabouts.

When starting out and you are not sure exactly what you want it is usually best to stick with the “kit lens”, that is the lens that comes with your camera when bought as a bundle. This is because they are usually not badly made and usually cover a range of focal lengths, that is they can “zoom” rather than being fixed at one length. This means that from opening the box you will be able to go from wide to telephoto and get a feel for what suits you and where you feel your lens is lacking (if at all). Most kit lenses cover 28-80mm (ish) or equivalent, some more, but most will be either side of 50mm. In years gone by the kit lens would on occasion be a 50mm fixed focal length lens and that is still the choice for some people who elect to buy the camera and lens separately.

When I say “or equivalent” that is because consumer level DSLR cameras do not have the same field of view as the pro cameras such as the Canon 1D and 5D series because of the size of their imaging sensors. Pro level cameras have a sensor roughly matching the image area of a piece of 35mm film whereas consumer cameras have much smaller sensors. The effect is while the lens is still measured the same the output image appears to “crop” the scene down. Therefore people talk about a “crop-factor”. This effect gives the impression of magnification, in the case of Canon entry-level cameras this magnification is 1.6x, with Nikon 1.5x. While obviously not the really the actual case it is a useful way of comparing lenses for what you need. This aside for all intents and purposes what you get with a 50mm lens on a Canon 350D or Nikon D70s is not what you would expect from a 50mm lens but more like 75mm or 80mm (if you have previous experience, if you are new to this stuff it is not going to make a bit of difference).

Apertures

As well as focal length the other major part you need to consider is the Aperture of the lens. This is how wide the lens “pupil” will open to allow light in relative to the focal length and is written as f/X where X is a number like 2.8 or 3.5. These numbers are “f-stops” and rather than being a straight measurement they in fact go up and down in steps, as the number increases you get half as much light as the f-stop preceding. Unlike many technical specifications the lower the number is considered to be “better” (but obviously depends on your specific application and circumstances) because the smaller numbers mean a wider aperture, that is allows more light, and therefore can be used in lower light situations. Lenses with smaller numbers (larger apertures) do not need as long a shutter speed to take the picture and are therefore considered “fast lenses“. For a fast lens you would be looking in the range of f/1 to no more than f/2.8.

Broadly speaking fixed focal length lenses will tend to be “faster” than zooms because it is easier and less costly to make them. My cheapest lens is also my fastest, the Canon 50mm f/1.8. Compare this to the Canon 350D kit lens, 18-55mm, the best it can do is f/3.5 which is far far slower.

Aperture though is not just about how fast the shutter speed can be. A wide aperture (small f-number) will also give the effect of blurring a background while a smaller aperture (high f-number) will keep more of the scene in focus. This is because the aperture has a direct baring on “depth of field“, that is how much of the scene is in focus.

Focal Distance and Macro

The minimum distance away from an object that a lens requires before it will focus defines whether a lens is suitable for macro photography. If you need to be able to get up really close to an object and magnify it for such as insects and flowers you need a macro lens. Macros allow you to get closer and for the subject to fill the frame. While some lenses can get reasonably close only dedicated macros can get very close and they tend to have better magnification capability than a standard lens used for this kind of thing.

Lenses and Photographic Applications

What type of photography will you do more of? The type of photography you do will determine what lenses you have in your collection or will help you decide that the kit lens is enough.

As mentioned earlier, while nowhere near a rule, on the whole a landscape photographer will tend towards wider angle shots. They will also, with obvious exceptions, want to keep as much in focus as possible so will favour smaller apertures.

Contrast this with portrait photographers. They will most often want to avoid wide angles because of the exaggeration affect on facial features, making noses bulge is not a path to profits in the portrait game. Many portrait photographers choose something in the 80mm+ range because it allows to take the shot at a distance (less in-your-face) and with a wide aperture so as to blur the background creating more emphasis on the subject. This purpose is precisely why I bought the 50mm f/1.8 mentioned above.

Sports and wildlife photographers really need to be able to get shots from great distances, they also need to be able to use fast shutter speeds as if they are too slow the action is either blurred or missed entirely. You are looking at 200m or greater and as good a aperture as you can afford. Some lenses include “image stabilisation” or “anti-shake”, this is a technology that counteracts camera shake allowing you to get shots with slower shutter speeds without blurring through unsteady hands.

If you need to be able to go from wide to telephoto without swapping lenses you will need a good zoom. While you tend to get better quality in the fixed focal length “primes” with zooms what you lose in quality and aperture you gain in flexibility.

When people talk about a good “walkabout lens” they tend to fall into the “general purpose prime” camp such as a 30mm or 50mm or a very flexible zoom. This is largely down to personal preference but forcing yourself to use one focal length can be an education.

Price and Brand

First-party lenses from Canon and Nikon will be more expensive than third-party counterparts from Sigma, Tamron, Tokina, etc. Either way the prices tend to go in bands, with cheap consumer models, mid-range up to pro models. The better performers will be in the mid-to-pro and the price will be reflected. As well as optical performance you can usually expect better build quality and weather-sealing in the very upper end. A top third-party lens will often perform comparably with a higher priced first-party lens. Make sure you check magazine or online reviews before purchasing any lens as you need to make yourself aware of any potential issues.

camera, lenses, dslr, tutorial

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