The answers to all the questions about lenses you've been afraid to ask

Camera lenses for beginners

What do all the numbers on camera lenses mean?

Focal length

If you look at the end of your lens you'll see a number followed by "mm". This is the focal length of your lens, eg. 50mm, or 40-150mm. If there is one number, it's a prime (or fixed focal length) lens. If there are two numbers, it's a zoom lens. The focal length is simply a measure how long the lens is. It's not exactly how long it is, but it's a good way to tell at a glance.

Standard lens: a 50mm lens is called a "standard" lens because the field of view is closest to the human eye. The field of view is how much of a scene you can actually see. Humans have a field of view of approximately 180 degrees. A rabbit's field of view is more like 350 degrees.

Wide angle lenses: a lens with a smaller focal length than 50mm is called a wide angle lens, because the field of view is wider than a human eye can see - more like the rabbit. Wide angle lenses are typically something like 20mm focal length.

Telephoto lens: lenses with a narrower field of view than standard are called telephoto lenses - eg. 180mm or 300mm. They not necessarily zoom lenses. Zoom lenses are any lenses with a range of focal lengths. You can have a fixed focal length telephoto (eg. 200mm), or you can have a zoom lens that has a telephoto range (eg. 70-210mm).

Closest focussing distance

You might find that when you get up close to something, your camera won't focus. It's because you are too close. Each lens has a fixed closest focussing distance, and the more expensive your lens, typically, the smaller this distance will be.

Aperture

You might have heard about aperture, one of the ways the camera controls how much light hits the sensor to make the photo. Did you know the aperture is actually in the lens, not in the camera? The aperture is an adjustable hole, and some of the numbers on the lens refer to aperture, not to the focal length. Have a look on the rim of one of your lenses and see where it says something like, "1:4" or "1:3.5-5.6". The number after the colon is the size of the largest possible aperture for that lens, so f4 in the first example. In the second example, the largest possible aperture changes with the zoom, so at the wide end the largest aperture is f3.5, and at the longer end it is f5.6.

This lens has a focal length of 55mm, and a largest aperture of f2.2

Crop factor

Just when you think you've got it, you need to understand crop factors. More expensive digital cameras typically have what is called a "full frame" sensor. The rest have what is called a "cropped sensor". A full frame sensor is the same size as 35mm film was: 36mm x 24mm.

If your camera has a cropped sensor it will have a smaller sensor. The effect this has on lenses is that it makes the effective focal length longer. My X-T1 has a sensor which is 23.6mm x 15.6mm, and this makes a 50mm lens have an effective (sometimes called "equivalent") focal length of 76.5mm.

To work out what the effective focal length is for your cropped sensor, you need to know the "crop factor" for your camera. Look it up online. For my X-T1 it's 1.53. All you do then is multiply the focal length of your lens by the crop factor: 1.53 x 50 = 76.5mm.

What this means for you: If your camera has a cropped sensor (and if you don't know whether it does, it almost certainly does have a cropped sensor*), you need do a bit of mental arithmetic. When you are reading about which camera a photographer used, and it says "50mm" (assuming they used a full frame camera), you need to do a bit of division to get an equivalent effect. So if a friend of mine was using a full frame camera and a 50mm lens, I would need to use a 33mm lens to get the same field of view (50/1.53 is about 33).

* I say this because full frame cameras are very much more expensive than cropped sensor cameras, and it's unlikely that you would have bought one without knowing about it.

What's a kit lens?

Entry level cameras are often sold with what's called a "kit lens". New photographers don't often know that you don't have to buy the kit lens - you can buy the camera body and lens separately. The problem with kit lenses is that the largest apertures are relatively small, and if you want to learn how to use aperture for creative effects, you will quickly outgrow a kit lens.

The good news is that a 50mm f1.8 lens is not too expensive, in the scheme of photography equipment. So if you only have a kit lens, and you find you enjoy learning about apertures and what they can do, you can upgrade to a 50mm f1.8 as your next lens.

What's a "fast" lens?

Some people refer to lenses that have a very big maximum aperture as "fast", eg an f2.8 or an f1.8 lens is fast. The larger aperture means they can be used with faster shutter speeds in low light, without getting camera shake or blurred images.

Which lens is best for portraits?

An 80mm or 100mm lens is often referred to as a "portrait lens" (full frame measurement). This lens allows the photographer to get close enough to the subject to chat without shouting, and it has a small degree of compressed perspective that is flattering to everyone. The converse is a wide angle lens which distorts portraits and gives the subject a big nose.

Which lens is best for landscape?

Usually, wide angle lenses are used for landscapes, to "get more in" the image:

But longer lenses can also be effective for intimate or isolated landscape shots:

Which lens is best for wildlife?

You usually want the longest lens possible, so you can stay out of the animal's way. A bonus is to have a faster lens so you can shoot in lower lights at faster shutter speeds, but these can get very expensive.

Shot from a boat with a 140mm lens (214mm equivalent)

Which lens is best for travel?

You might want to take your 70-210 f2.8 lens with you everywhere you go, but it's a beast. You'll thank yourself if you take a lighter zoom lens and sacrifice the larger aperture. Carrying heavy kit round hot and dusty places does not make for a relaxing holiday. Or just use your phone?

What specialist lenses are there?

Fisheye lenses: ultra wide angle lenses that distort the image dramatically:

Tilt-shift lenses: lenses that allow you to manipulate the plane of focus independently of the camera. Useful for architecture photography which tends to suffer from converging verticals otherwise.

Macro lenses: a macro lens reproduces your subject at life-size or larger. This is possible because of the physics involved in the lens construction which allows closer focussing than is achieved with normal lenses. Whilst shooting macro you lose the ability to focus on the horizon, but you don't need that when you're shooting close up. When not shooting macro you use it just as a normal lens.

Lensbaby: this is a lens manufacturer that produces lenses that create very soft out of focus areas (known as "bokeh"): https://international.lensbaby.com/

Jargon

A "DX" lens is a Nikon lens designed to be used on a Nikon cropped frame camera.

An "FX" lens is a Nikon lens designed to be used on a Nikon full frame camera.

If your full frame camera has DX mode, you can use a DX lens on it.

I'm a Canon user, lately a Fuji user, and I'll hold my hand up and say the Nikon lens system confuses me. I did find this post which might help: How To Read Your Nikkor Lens Barrel

"EF" lenses are Canon lenses. EF-M lenses are designed to be used on Canon mirrorless cameras. EF-S lenses are designed to be used on Canon cameras with an APS-C sensor.

Canon "L" series lenses are their professional range: higher quality glass, more weatherproof and with wider maximum apertures. They have a red band around the front of the lens. As far as I understand it, Nikon don't have an equivalent "pro" designation on their lenses. But if you know differently please let me know.

Are third party lenses any good?

Yes, is the short answer. Quality varies though, so do your research online - there are plenty of opinions out there. Sigma and Tamron are the two best known.

Should you use UV filters on your lenses?

You can buy screw-on clear filters for the front of all your lenses. Camera shops often try to sell them to you, telling you they protect your lens from dust and scratches. But you are putting a cheap piece of glass in front of an expensive piece of glass - and the net effect is as good as the cheap piece. I don't use UV filters on my lenses, but I accept that if I drop it or scratch it, I will need to pay to have the whole front element replaced. I can't advise you one way or the other on this one.

So: which lens should you use?

I hope you can see now that the answer to this question depends on what you are shooting. If you need to be far away, you'll need a telephoto lens. If you need to be close up, you'll need a lens with a close focussing distance. If you need to fit a lot into the frame, you'd choose a wide angle lens. If it was important that you had no distortions, you'd pick a 50mm equivalent.

If you're looking for the first lens to buy after you've outgrown your kit lens, a 50mm f1.8 will give you the best aperture range to work with, but you do have to zoom with your feet.

Header image Tom Pumford, with permission