Home: Basic Photography: Camera Lenses

Talk to me about Camera Lenses!

Talk about camera lenses? That's a subject near and dear to my heart! Nothing says photography like great glass, and that's what's at the heart of today's great camera lenses.

Acquiring lenses is a big step that no serious photographer should take lightly. Your lenses should give you decades of good service, so choosing carefully is a given. Understanding the jargon that describes photography lenses is also a necessity.

Fortunately for the "right-brain" types among us, understanding lenses is not just tech-speak. Lenses allow us to see the world in unique ways that allow our creativity to shine. With that in mind, read on!

But before we start our conversation about photography lenses, here's what's in store in this Basic Photography section, in order:

What are camera lenses for, anyway?

The basic job of photography lenses is to gather light and focus it on to light-sensitive film or a digital sensor that resides in the camera. Sounds simple enough, but from here it gets interesting. Listen up, because understanding camera lenses is essential when learning macro photography...or any kind of photography, for that matter!

All camera lenses are made of glass elements arranged in fantastic combinations in a marvel of engineering that's way beyond my ability to interpret. Depending on the way the glass is ground, and how the lens elements work together, finished camera lenses gather light from a variety of viewing angles. We call this focal length, and all camera lenses range from wide angle to telephoto.

For photography lenses, the lower the focal length (expressed in millimeters, or mm), the wider the angle of view.

Since 35mm cameras with interchangeable lenses have been the industry standard for decades, I'll use the common focal lengths for these cameras as the starting point. Here's are some focal lengths you'll see frequently, in a by-no-means-complete-listing:

Ultra-wide "fish-eye"	Wide-angle focal lengths				"Normal" focal length	Telephoto focal lengths				Super- telephoto
18mm and below	20 mm	24 mm	28 mm	35 mm	50 mm	80 mm	105 mm	135 mm	200 mm	300mm and above

Photographing the same scene with different focal length camera lenses can lead to wildly different results:

	Here's a harbor scene, photographed with a 20mm wide-angle lens...
	...and with a 50mm "normal" lens...
	...and with a 200mm telephoto lens. Compare the size of the boats here, and inside the boxes above!

Coverage circles

Camera lenses project a circle of light, or coverage circle, onto the camera's film or digital sensor. Obviously, this circle must be large enough to cover the light-sensitive area, otherwise there would be an annoying fall-off, or vignetting, towards the edges of the photograph.

Deciding whether a particular lens of a given focal length is a wide-angle, normal, or telephoto depends on the size of the film or camera sensor. The larger the area to be covered, the longer the lens focal length required.

Digital cameras of recent vintage usually have sensors that are smaller than the 24 x 36mm dimensions of a 35mm camera. It takes a shorter focal length camera lens to cover these smaller chips, resulting in a range of available lenses with shorter focal lengths across the board. Here's a comparison of camera lenses with analogous angles of view (values approximate):

35mm camera, 24 x 36mm film area	35mm	50mm	70mm	105mm	135mm	200mm
Digital chip equivalent, 15.6 x 23.7 mm (Nikon D70)	24mm	35mm	46mm	70mm	90mm	130mm

Camera manufacturers often list a magnification factor in their literature that can be used to convert 35mm focal lengths to their smaller-chip equivalents. A factor of 1.5, for example, means a 35mm lens used on a smaller-chip camera has a similar perspective as a 50mm lens used on a 35mm SLR camera. This can help when comparison shopping, or when using interchangeable lenses that fit both style of camera.

Since most digital cameras have smaller chips than the frame size of 35 mm film, they require a shorter focal length lens. For example, 50mm camera lenses are considered normal lenses in 35mm photography, but would be in the telephoto range if attached to a digital SLR with a smaller chip.

In the interest of consistency, I will refer to camera lenses by their35mm equivalent focal lengths, realizing that my reader may have to make a conversion based on his/her own lens. Please forgive me if that creates confusion!

Lenses and perspective

Photography lenses are an exciting way to look at the world because of the way different focal lengths change the perspective of objects in the frame. Try this: Attach a wide-angle lens to your camera and walk around a room just looking through the viewfinder. Notice how wide-angle exaggerates the relative sizes of objects close to you, and how more distant objects show up tiny.

Now try a telephoto lens, and notice how the distances between objects is compressed. Making the most of lens perspectives is one of the keys to creative photography, so consider this lesson essential!


A long lens (200 mm) compresses your subject in space. Such selective focus frees her from her surroundings...	...whereas a wide-angle lens (28 mm) exaggerates subjects close to the camera relative to the background . PS: That's a bowl of Michigan blackberries!

So what, then, is a "normal" lens? It's a lens focal length that sits in between the distorting qualities of wide-angle lenses and the scene-squishing properties of telephoto. Some define a normal lens as having the same focal length as the diagonal measurement of the film or sensor.

Normal lenses show a perspective on the world that most closely mimics that of our own eyes....

...however...

...don't confuse the normal perspective qualities of a normal lens with field of view. Healthy humans have a visual field of close to 180 degrees side-to-side, but a normal lens covers only 40 horizontal degrees of that field.

That's okay, because we're not asking camera lenses to mimic the exact way we see our world.

One of the beauties of photography is that, through the optics of different lenses, we're offered a view of our surroundings that's entirely different from our own vision.

Setting focus

Almost all camera lenses have some way of changing the focusing distance (this can be done manually or via auto-focus). While all lens can focus to infinity, lenses vary in how well they can focus in the near range. Close-focusing ability is the special domain of macro lenses. There are also a number of ways we can enhance the close-focusing capabilities of other, non-macro lenses. That's a larger topic that I cover in more detail here.

Fixed vs. zoom lenses

Photography lenses have either a fixed or a variable focal length; the latter are more commonly referred to as zoom lenses. When identifying lenses we list the focal length first followed by the maximum f/stop, or aperture (more on this here). For example, a 85 mm/1.8 is a lens with a fixed 85mm focal length, and a 35-105mm/4.0 can be "zoomed" to any focal length between 35 and 105mm.

In the digital world, you'll encounter the competing terms optical zoom and digital zoom. Optical zoom is the only one you should care about, because it refers to properties of the lens itself. Digital zoom is just a software function, and is nothing more than cropping into the image electronically. Don't be fooled!

Fast vs. slow lenses

We also classify lenses by their light-collecting ability. So-called "fast" camera lenses will have a wider front lens diameter than their slower counterparts. If you think about it, it makes sense that a larger surface area will be able to gather more light to send back to the film or sensor.

Remember how lenses are identified? When judging the speed of a lens, look for the f/stop number listed after the focal length. We'll discuss aperture in detail later, but for now remember only this: the lower the f/stop number, the more light can enter the lens, resulting in a faster lens. For example, a 50mm/1.4 lens is faster than a 50mm/2.0. Here are the pros and cons of fast vs. slower lenses:

Fast lens pros: Brighter viewfinder image, more precise focusing
Fast lens cons: Higher cost, heavier
Slow lens cons: Darker viewfinder image, precise focusing more difficult
Slow lens pros: Lower cost, lighter

Lens sharpness and optical quality

A lot of ink gets spilled on this subject. Thanks to the hard work and talent of legions of optical experts, and a boisterous community of users of fine optics (which includes photographers, astronomy buffs and birders, to name the most prominent) lens design and optical quality has been pushed to the outer limits of what is physically possible. As a result, today's photographic lenses, telescopes, and binoculars are better than they've ever been.

Optical clarity and sharpness are essential qualities of a photographic lens. Resolution targets are available to bench-test lenses under controlled circumstances, and the results allow us to objectively compare lens sharpness.

I have bench-tested many lenses that I've considered buying, and I've gotten good information for my efforts. However, I've had to be careful not to value sharpness above all other lens qualities. I don't want to be the guy who is more concerned with the last iota of resolving power than with the feel of the lens' images (these guys are out there, I've met them). That's not how I want to approach my photography.

I've moved away from rigorous testing as a result, and now, to me, the proof is in the photograph alone. Having run a lens through its paces, photographing a variety of subjects under different lighting conditions, and viewing the results on the monitor (for digital images) or through a good magnifying loupe on a light box (for film), I choose to trust my eyes with a live subject rather than by gazing at the lines on a resolution target.

But that's just me. If that makes me a less discerning photographer, so be it. For those who want more objective evidence, it will be worth your while to test a lens by photographing a resolution target, and comparing the results to either a known standard or a lens you know and love.

The 1951 USAF resolution test target is a well-known target you can find with a quick online search; make a high-quality printout of the image file on high-quality, glossy paper (test targets are also available at most camera stores). Mount your camera on a tripod, focus precisely, and make a series of photos using different f/stops and focusing distance. Place a target off-center to check edge sharpness. Review the pictures carefully, and judge accordingly.

Fortunately, quality standards for photo lens manufacturing are very high, and it is extremely rare to find a true dud of a lens. Most lenses, even non-interchangeable lenses on compact cameras, are quite good. In fact, the resolving power of most lenses exceeds that of computer monitors!

Keeping lenses clean

Clean lenses make the sharpest photos possible. Dirty ones don't! When you're photographing, it is hard to avoid getting unwanted stuff on your lens. To avoid getting dust particles, smudges, fingerprints, and other undesirables on your front lens surface, develop good habits. I recommend:

Using your lens cap. Not only does it keep grime off your lens, it can protect it from breakage if the going gets rough-and-tumble.
Using a lens shade. These are mostly used to avoid lens flare, but they also provide a barrier that keeps fingers and other undesirables away from the lens surface.
Keeping your fingers off the glass! No matter how clean you think your fingers are, they are greasy enough to leave a smudge on your lens. If you see a hair or dust bunny on your lens, don't try to swish it away with your fingers. You'll regret it. Fingers off!

To clean a lens that is obviously smudged, dusty, or dirty, follow these steps:

Blow off the lens surface with a bulb blower. Please don't blow on the lens with your mouth: you will launch spit drops on the lens, and will have a bigger cleaning job ahead.
If this fails, a clean brush made for lens cleaning can brush away stubborn dust particles. Store these in a zippered plastic bag in your camera bag. Brushes can't remove fingerprints or smudges, in which case you'll have to....
Use lens paper (made for cleaning lenses: no tissue paper!) to wipe away the smudge. Make sure that all dust has been blown off before doing this, because a trapped dust particle can scratch your lens, and you won't be happy about that!
If all else fails, use a lens cleaning fluid and lens paper. Always drop fluid onto the paper, never directly onto the lens. Wipe gently in a circular motion from the center of the lens toward the outside.
Don't aim for perfection. Get rid of the major grime, and quit before you go overboard. Cleaning a lens carries a slight risk of scratching the lens surface, so tread as lightly as you can.

Filter threads

All SLR lenses, and many other fixed-mount lenses, have a female filter thread on the inside front of the lens barrel. We use these threads to attach filters, close-up lenses, and other accessories.

Not all camera lenses will have the same diameter, but fortunately there is standardization across the range of different manufacturers. The filter diameter of your lens can be found by looking at the inside surface of your lens cap. 49, 52, and 59mms are typical sizes. Expect to pay more for filters with a wider diameter, because good glass costs money!

Lens mounts

Finally, it's important to know that lens mounts for interchangeable camera lenses are brand-specific. So, no fitting your Nikon lens on a Canon body, kids, sorry, it won't work. Adapters are available if you have no other choice, but that's not a great long-term solution.

With one notable exception, all camera and lens manufacturers have changed their lens mounts at some point in the development of newer cameras. For example, lenses to the popular Canon EOS series will not fit older Canon bodies. The exception is the Nikon company, which has kept the venerable "F" lens mount on its cameras for decades. That means older camera lenses fit newer bodies and vice versa (although electronic communication between body and lens will not necessarily remain).

All photographers have to eventually decide in which manufacturers camp they are going to dwell....I sincerely hope this site will give you valuable tools to help you make your decision, whether you are learning photography or are an experienced shooter!

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