Photography for Beginners Part 10: Focal Length

Each post in this series builds on information discussed in previous posts. See the Photography for Beginners page on the menu for links to all the posts.

Part 9:  Exposure Metering

.

In this post we’re going to discuss lens focal length and related topics.

What is focal length?

There is a bunch of technical specifications and math involved in what focal length actually measures. It has to do how light is bent by a lens and the distance from the plane of the film or sensor to the point of infinity focus. Or something like that. Thankfully we don’t need to actually understand the physics in order to know how focal length applies to photography in practical ways.

Focal length is measured in millimeters, and what you do need to understand is what the numbers mean in general terms. A short focal length (low number) provides a wide-angle of view. A long focal length (high number) provides magnification and a narrow angle of view.

Focal Length Categories

If you want to take a photo of a really large scene you want a short focal length. This is called a wide-angle lens. Wide angle usually refers to lenses of around 25mm or shorter.

If you want to take a photo of a small area of a scene you want a long focal length with a narrow angle of view. These are called telephoto lenses. There is some disagreement over where exactly the telephoto range starts. Some say it’s anything over 80mm, others argue it’s at least 135mm and longer.

Normal or standard focal lengths fall into the 35-80mm range.

Two other aspects of focal length, aside from angle of view, are magnification and distortion.

Since a wide-angle lens fits a lot of what you can see into a photo, everything in the photo will look farther away and smaller than it does to your eyes. Think of it as sort of reverse magnification.

A very wide-angle lens, like 12mm, can cause distortion of nearby objects at the edge of the frame, making them look like they are leaning. This can be taken to an extreme with fisheye lenses, like 8mm, which make objects look rounded.

With a telephoto lens you can make small or distant objects take up a large part of the frame. The lens has powerful magnification and makes the objects closer or bigger than what you see with your eyes.

A telephoto lens also causes compression in an image. Objects in the background appear to be much closer to objects in the foreground than they are in reality. The distance is visually compressed.

A 50mm lens produces photos considered the closest approximation of what you see with your eyes in terms of distance and size. That’s why it’s a popular focal length.

So focal length choice depends on the size of your subject, how distant you are from the subject, and whether you want to include or avoid types of distortion.

Full Frame Equivalent

Here’s the tricky part. Focal length numbers don’t always mean the same thing in terms of actual results. A 50mm lens on a compact point and shoot (P&S) camera isn’t the same as a 50mm lens on a DSLR (digital single lens reflex) camera.

The majority of digital cameras out there have what are called cropped sensors. This means the sensor is smaller than a 35mm film frame, the standard film size for the final decades of film camera dominance.

There are four main sizes of sensors used in crop sensor cameras. (Cell phone camera sensors are even smaller and not included in the four.) Some cameras, primarily DSLRs, have what is called a full frame sensor, which is larger than the others and replicates the 35mm film size.

The size of the sensor impacts the angle of view of a lens. A lens at the longest end of wide-angle on a P&S might be a 9mm focal length. But 9mm is an extreme wide-angle on a full frame camera and would have a lot of distortion.

So in order to make discussions of focal lengths less confusing, photographers use “full frame equivalent” as the standard.

That’s what I did in the categories section above. All the focal lengths I mentioned were the full frame equivalents. The actual focal lengths may be different, based on your camera’s sensor size. For instance, my camera has an APS-C sensor, which is one size smaller than full frame. The 18-55mm kit zoom lens that came with it is equivalent to a 27-84mm full frame lens.

When you look at camera and lens specifications, the product listing will almost always give the actual focal length and the full frame equivalent if it’s for a crop sensor camera.

This standard allows everyone to know exactly what they’re getting when shopping for gear and the ability to engage in general discussions about focal lengths without having to do conversion calculations for sensor size each time a focal length is mentioned.

I’m not sure how common this is, but the focal length scale in the viewfinder for my Panasonic bridge camera’s zoom lens displayed the scale using full frame equivalents. So even while out shooting I had the standard numbers right in front of me to make things easy to comprehend.

The metadata stored in image files usually records both the actual and 35mm equivalent focal lengths used.

Zoom Lenses

Most P&S cameras have a zoom lens, and zoom lenses can be purchased for ILCs (interchangeable lens cameras).

A zoom lens doesn’t have a fixed focal length. A P&S camera zoom lens usually goes from a wide-angle to at least some amount of telephoto. Super zooms have a very large focal length range. Zoom lenses for ILCs usually have a smaller range of focal lengths.

The advantage of zoom lenses is their flexibility and convenience. You can take a wide-angle scenic shot, and then literally turn around and zoom in on a nearby flower for your next shot.

If you have an ILC, a zoom lens can also cut down significantly the number of lens changes you need to make. A zoom lens with a broad range is a good choice for a travel lens because you only need to pack one or two lenses to cover a wide variety of situations. I’m a huge fan of zoom lenses for all these reasons.

The main disadvantage of zoom lenses is that they usually aren’t as sharp. This tends to be especially true at the longer focal lengths of super zooms. The complex design and construction often necessitates giving up some quality in exchange for flexibility. They can also be big and heavy.

Another disadvantage is they usually don’t offer a really wide aperture, and most have a variable aperture. (The widest aperture allowed varies depending on focal length being used.) For these reasons there are some photographers who rarely to never use zoom lenses.

There are exceptions to the disadvantages. There are f2 and f2.8 constant aperture zoom lenses on the market and some zooms are high quality. My 83-300mm equivalent variable aperture Fuji zoom lens is really sharp and fairly compact. (I’m in love with that lens!) But the saying “you get what you pay for” is true here. High quality zooms have high price tags, most especially the constant wide aperture zooms.

Prime Lenses

A prime lens has a fixed focal length. So if you buy a 50mm prime, that’s what you get, 50mm and nothing else. You’ll rarely see them on P&S cameras, but primes are the first choice for many photographers with ILCs. Some photographers shoot only with primes and completely shun zooms.

The advantage of prime lenses is that it’s easier to find a high quality lens. Because the lens construction is less complex than a zoom, all the design focus can go into getting that one focal length right. (Though there are certainly less than stellar prime lenses for sale out there too.)

Another advantage of primes is that there is a wider variety available, making it easier to fit a lens to both your interests and budget. Maybe you have a preferred focal length and want to sink your money into one really good lens. A set focal length might be available in f1.4, f2, and/or f2.8 versions. The f1.4 is going to be expensive, but the f2.8 might be quite reasonable.

Primes also have the advantage of being smaller and lighter than zoom lenses, especially the high-end zooms with a constant, wide aperture. If compact size is one of your top needs, a prime lens helps with that.

The disadvantage of primes is that if you enjoy shooting a variety of types of subjects you’ll be carrying around more lenses and you’ll have to change lenses more often, which can be really inconvenient at times. Aside from the inconvenience, every time you swap out lenses you expose your camera’s sensor and more dust and other particles can get stuck to it.

Zooming with Your Feet

With a prime lens you don’t have the convenience of a zoom. You have to “zoom with your feet” instead of the lens. This means physically moving yourself and the camera closer or farther away in order to get the shot you want. Sometimes that’s easy to do, other times it’s impossible due to barriers or topography. (I like to discourage my readers from zooming with their feet over a precipice.)

Many argue, I think rightfully, that the disadvantage of having to zoom with your feet is actually beneficial because it forces you to learn more about composition and be more creative. A zoom lens is often used as a crutch. (I fully admit to fully using my zooms as crutches.)

Even if all you have is a zoom lens, you can still go out shooting while restricting yourself to a single focal length to see how that might improve your photography skills and creativity.

X Zoom

Zoom lenses for ILCs are always advertized by their focal length range. But the fixed (meaning not interchangeable) zoom lenses on P&S cameras are usually advertized with an X number. A 7X zoom or 40X zoom.

The X number refers to magnification, not focal length. A 22X zoom magnifies up to 22 times.

It’s possible for a 16X camera and an 18X camera to both have the same longest focal length. That’s because the X number is based on the starting (shortest) focal length. So a lens with a 22mm widest angle will need more magnification (a higher X number) to reach the same longest focal length that a 24mm lens needs.

The X number is an indication of how much range the lens has, but not what the range actually is.

If you’re confused, don’t worry about it. The only time you really need to understand this is when shopping for a new P&S camera. If you do go shopping for one, pay attention to what the listed focal lengths for the lens are and not the just the X number. That’s the only way to tell for sure if the lens is wide enough or long enough for how you plan to use the camera.

Digital Zoom

Most P&S cameras have a digital zoom feature. Optical zoom is what your lens can do natively with its physical optical components. Photos taken using optical zoom will be the best your camera lens can produce.

Digital zoom allows you to zoom even closer than the lens optics allow, but this is accomplished with camera computer and sensor trickery.

Digital zoom usually produces poor to craptastic results, especially if the sensor and lens aren’t that great to start with. You’re usually better off using optical zoom only and then cropping the photo, though that has serious limits as well.

I’ve tried digital zoom quite a bit, but in my experience the resulting photo has such poor image quality there wasn’t even any point to taking it. So my advice is to turn off the digital zoom feature. That way you won’t accidentally use it.

I do have a couple exceptions to this advice, however.

My Panasonic bridge camera has what they call Intellizoom, or something like that. It’s an enhanced digital zoom that works on a focal length range between the end of optical zoom and full normal digital zoom. If I only needed to go slightly over the optical zoom range it sometimes produced okay photos. The last half of the Intellizoom range usually produced the expected digital zoom crud. If your camera has a similar feature you can experiment to determine how much of it is useable.

The other exception is when you want a “look what I saw!” photo. You’d rather have a crummy photo than no record of the event at all. Maybe you see a bear in the distance or something. You won’t win any wildlife photo contests with the image, but at least you have a memento.

I’ve done this for IDing birds. I know the digitally zoomed bird pic won’t be pretty to look at or worth keeping. But I’ve often managed to capture enough smeary details to at least go through my bird book once back home and figure out what it was I saw.

Minimum Focus Distance

Minimum focus distance is the shortest distance there can be between your lens and your subject before it’s too close to focus on. This distance can be measured in inches or feet.

Let’s say the minimum focus distance of your lens is 6″ and you’re trying to take a close-up of a flower. If your lens is only 4″ from the flower it will be blurry no matter what. You need to move the camera back to create at least 6″ of space.

Minimum focus distance is roughly, but not exactly, related to focal length. By not exactly I mean that two different 50mm lenses could have two different minimum focus distances.

By roughly I mean that in general, the longer the focal length of the lens is the longer the minimum focus distance is. If you have a wide-angle lens the minimum focus distance is inches. If you have a telephoto lens the minimum focus distance is feet. If you have a zoom lens the minimum focus distance probably changes as the focal length changes.

You need to pay close attention to the specs for your specific lens. Sometimes the minimum focus distance listed is from the front of the lens, and sometimes it’s from the sensor. A listed distance from the front lens element is easy to imagine and put into use. If the listed distance is from the sensor you need to picture a plane through the middle of your camera body and mentally measure from there. So the usable distance from the front lens element will be much shorter than the listed distance.

Macro Lenses

Most P&S cameras have a macro feature you can turn on. Some ILC lenses are macro lenses. Macro lenses aren’t limited to wide-angle. You can buy a 60mm prime macro lens, for instance.

A macro lens has an extremely short minimum focus distance so you can get all up in your subject’s grill. This is especially useful for flower, insect, and product photography. By getting your lens so close to your subject you can fill the frame with it.

Putting Focal Lengths to Work

There are some generally agreed upon best uses for different focal lengths.

Wide angle lenses are good for landscapes and astrophotography. Longer wide-angle to shorter normal lengths are popular for street photography. Longer normal to shorter telephoto lenses are good for portraits. Long telephoto lenses are good for wildlife and sports.

But these are far from hard rules. A telephoto can allow you to pick out a small section of a landscape for a different perspective and composition. Getting very up close and personal with a wide-angle on a portrait subject can produce interesting results, and so on.

It’s best to gain a solid understanding of what the various focal lengths are good at as you’re starting out, along with what their weaknesses are and what potential visual distortions they can produce. It’s frequently the case that you want to go with the tried and true in order to produce a visually pleasing or classic image.

But don’t be afraid to experiment.

Zoom lenses make experimenting easy. Take multiple photos of the same subject at several different focal lengths. You might be surprised by which one jumps out at you as being the most interesting because you captured an unexpected perspective of your subject.

Try the opposite too. Choose a focal length for your zoom lens and leave it there. Don’t give in to temptation to change it, even just a little. Experiment with how that focal length affects your choice of subjects and your decisions about composition, etc. If you’re accustomed to using a zoom lens as a crutch (like me!) this exercise can be difficult. But you might be pleasantly surprised by the results.

Examples

This series shows how taking multiple photos of the same subject using different focal lengths dramatically alters not only what is seen, but how the subject is conveyed to the viewer. (Shot with the zoom on my bridge camera.)

Photo #1 is at 41mm. Pretty yucky photo. The fence in the foreground is just clutter and you can barely see the tree and barns.

Photo #2 is at 160mm. It’s okay, but it’s more of a factual “I saw these barns” photo than anything else. That’s not always a bad thing. When traveling you often want documentary type photos as a visual diary of your trip. But such photos have little in the way of artistic merit.

Photo #3 is at 370mm. Better in my opinion. By zooming in and only framing one of the barns the photo conveys more intimacy and less of a documentary feel.

Photo #4 also at 370mm. This photo shows how using the same focal length, but changing the composition slightly, can have an impact. It’s still not a photo I would frame for display, but it’s the most interesting of the bunch to look at in my subjective opinion.

Part 11:  RAW vs. Jpeg

Comments or questions always welcome!

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s