DSLR Lenses: 7 questions photographers must ask about their next piece of glass
Choosing new DSLR lenses can be a bit of a minefield. To help you with your choice we’ve (asked and) answered 7 of the most important questions you need to know about your next optic.
I’m using the zoom lens that came with my camera, but I’d like to add one or two more. Where do I start?
Lenses can be split into three basic types: wide-angle, standard and telephoto. The zoom lens that came with your camera offers a focal length in the region of 18-55mm, giving a wide view at the 18mm end and a standard-ish view at the other – depending on the camera it’s attached to.
A good tip for choosing which new lens(es) to go for is to avoid duplicating your existing focal length range where possible. Take a look at lenses that offer either a wider or longer focal length, depending on the type of things you mainly take pictures of.
But do upgrade your kit lens as soon as you can afford to. It’s been built down to a price so that it can be bundled with cameras, and doesn’t feature the sharpest or brightest glass around.
You’ve mentioned focal length three times. That’s how long a lens is, isn’t it?
Not exactly, but without getting caught up in the magic of physics, think of it this way: focal length has an effect on how much of a scene you can see through the lens. Wide-angle lenses have short focal lengths (such as 10mm) and a wide-angle of view – hence the name.
Some of the widest lenses available can take in almost a 180° view of the scene, and with a lens this extreme you need to make sure you don’t accidentally include your own shoes in the frame.
As the focal length of the lens increases, this viewing angle decreases, to the point where long telephoto lenses of 400mm and above only take in a very narrow view of a few degrees.
OK, so how does a standard lens fit in?
A standard lens for a full-frame digital SLR is 50mm, and it captures roughly the same view as the human eye. However, the smaller ‘APS-C’-sized sensor inside the majority of DSLRs is around 1.5x or 1.6x smaller than a full-frame one.
Subjects appear bigger in the picture, a bit like if you’d cropped a shot in Photoshop, and to get a similar result with a full-frame DSLR you’d need to use a longer lens.
So, a 50mm lens fitted to a regular SLR actually gives you a ‘full-frame equivalent’ focal length of 75mm (50mm x 1.5).
To get the standard angle of view that a 50mm lens gives you on a full-frame DSLR, you need to use a 35mm lens on most other cameras (35mm x 1.5 = 52.5mm).
Nice maths. So, what’s the point of a standard lens?
Pictures produced by standard lenses have a natural quality that lets a viewer concentrate on the subject of the photo. A 50mm prime – the ‘nifty fifty’ – is a great value all-round lens, ideal for portraits, street photography, still lifes and more.
What do you mean by ‘prime’ lens?
Primes are lenses with a single, fixed focal length – such as 24mm, 80mm and 100mm – and the only way to make the subject bigger or smaller in the frame is by using your feet.
Zoom lenses are more convenient as they cover a range of focal lengths. However, you often pay for that convenience with increased weight and compromised optics – primes generally produce sharper pictures and have faster maximum apertures.
Some of the more extreme focal lengths – such as thumping great 800mm telephoto lenses – are only available in prime lenses, too.
So when should I use a telephoto?
Long telephoto lenses are the mainstay of sports and wildlife photographers, as they can’t get close enough to their subject, yet still need to fill the frame, and telephotos enable them to do just that.
Short ones start with a focal length of around 85mm, with long ones stretching to 800mm and beyond.
These big guns are able to produce an effect called ‘compression’, where objects look closer together in the frame than they actually are.
This effect can be put to great use when composing a scene with ‘stacked’ elements – such as a line of colourful boats in a harbour. Telephotos are also fantastic for picking out details in a wider scene.
Do I need a wide-angle lens if my kit lens starts at 18mm?
On most DSLRs, that 18-55mm kit lenses actually give you the equivalent view of a 27mm-82.55mm lens on a full-frame camera. To get a true ultra-wide view, you’ll have to look at lenses in the region of 10mm.
These lenses show heavy distortion at the edges of the frame, and subjects closer to the lens will seem much larger than distant ones. Compose your shot to embrace (or avoid) these effects.
PAGE 1: Common questions about choosing DSLR lenses
PAGE 2: How to buy a second-hand DSLR lens – free cheat sheet
PAGE 3: Getting the best from your DSLR lenses
DO or Di? Your lens markings explained
Test your lens’ sharpness
9 things you need to know about using super-telephoto lenses
Full frame sensor size explained: how to exploit its advantages and cool effects
on Friday, February 15th, 2013 at 11:30 am under Photography Tips.
Tags: buying guide, hot, lenses, photography cheat sheet