Prime Time

Who wants a lens with a fixed focal length, a lens that can’t zoom in and out?

Prime lenses (as they’re called) are so 20th Century. Old fashioned, static and boring. Who buys them nowadays?

They come from the days … not so very long ago … when the mathematics required for designing a good zoom lens was daunting. Designers needed to work out how the light rays were going to pass through the various lens elements, from every possible angle and at every possible setting. And if their first design didn’t work out properly they had to start all over again with a tweaked configuration. Those early zoom lenses took months, if not years to design, so only the richest and most sophisticated photographers could afford them.

That’s all changed with the advent of the computer. Computers crunch the numbers so fast and so effectively that designing zoom lenses is now a doddle … almost.

Now every Tom, Dick and Henri has a zoom on their camera. The smallest and cheapest point and shoot will have a zoom on it that would have made a professional photographer’s jaw drop thirty or forty years ago. And there are some amazing lenses available – the Tamron AF18-270mm lens, for example, with a massive 15x zoom ratio.

So who wants a boring old prime lens?

I do.

Zoom lenses are great, but primes have a number of distinct advantages.

• They are far, far easier to design and construct, so they cost less. You get cracking value for money with a prime.
• They outperform all but the most expensive zooms. Compare these two photographs. The top one was taken with a 50mm prime lens. The second was taken with a good quality zoom, (from the same manufacturer) set to 50mm. They were taken at the same time, under exactly the same lighting conditions, one after the other. No post processing has been done to either. Except for resizing to fit the screen, they are precisely as they came out of the camera …

Now take a look at a portion from the top left corner at 100%

50mm prime, the top left corner at 100%

Zoom at 50mm, top left corner at 100%

The difference is clear. The prime lens gives a sharper image and the colours are more vibrant. And the prime was about half the price of the zoom.

This is not to say that zoom lenses are inferior. It all depends on what you need. Both types of lens have other advantages and disadvantages …

Speed

Prime lenses have the edge here. They can be made fast (i.e. have a wide maximum aperture) without becoming prohibitively expensive. The 50mm prime I used to take the first photograph has a maximum aperture of f1.4, allowing me to take photographs in semi-darkness. As far as I am aware there is no f1.4 zoom lens manufactured anywhere in the world. I’m not even sure if it’s physically possible.

Having a fast lens means that, in any given light, you can use a higher shutter speed (or smaller aperture). This is important if you are trying to photograph fast-moving action in low-light conditions – sport or wildlife, for example. Sometimes, in such situations, a prime lens is the only answer.

Another advantage of having a large maximum aperture is its depth of field. When the lens is wide open the depth of field will be so shallow that any distracting background will be beautifully blurred. Ideal for portrait photography.

Size/weight

This is another area in which prime lenses beat zooms. Because of their simpler construction they are a lot smaller and lighter than zooms.

Versatility

Zoom lenses are more versatile than primes. With a zoom you can can quickly compose and capture fast-moving action. You can also try a number of different compositions of the same subject within seconds. If you’re using a prime lens, your feet will have to do the zooming. And that changes the perspective. Zoom lenses are good for situations where the composition of your shot may change rapidly – sports and wildlife, for example … provided there is enough light.

Dust-busting

Dust getting on the sensor is the bane of a digital photographer’s life. And some people say that zoom lenses add to this problem because, when operated, they act as air pumps drawing air (and dust) into the camera. Some do and some don’t. It all depends on the way in which the zoom operates. Some have the moving parts entirely enclosed, so the lens does not change length and volume when operated.

It could be argued that, in fact, prime lenses add more to the dust problem because they have to be changed more often.

So, the jury is out on this one. It all depends on what sort of zoom lens you have or how you use your prime lenses.

Creativity

This is another aspect in which the jury is out. Some argue that using a prime lens encourages you to be more creative. With a zoom lens, the tendency is to stand in one position and zoom in and out to compose. With a prime lens you have to physically move around into different positions … farther/nearer … up a bit/down a bit. And moving around can only be good for your photography.

Other say that’s rubbish, “… after all, you can temporarily tape a zoom lens to a fixed focal length, can’t you? That will give the same effect.”

Yes, it will. But, having bought an expensive zoom, who’s going to do that with it?

The upshot is, as with all these situations, there is no one single answer. It all depends on what you want to achieve and how much money you have to achieve it.

But one thing is sure – don’t dismiss prime lenses as old-fashioned. They still have great advantages.

I’m off to a photo market early tomorrow morning, hunting for a bargain. And the bargain I’ll be looking for?

You guessed it.

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