Lens codes

Learning goal

You will be able to understand what a lens can do by reading the markings and symbols on its body. You will decode focal length and maximum aperture even in markings such as "1:1.8" or "1:3.5-5.6"; you will find the symbol that shows the filter diameter; you will tell apart what the minimum focus distance and the magnification ratio describe; you will recognize what the switches on the body are for; you will read manufacturers' own abbreviations from the manual; and by looking at a lens's minimum focus distance, you will explain why in a portrait you should stay away from it, at a distance that keeps a face's proportions on every skin.

The question

One Sunday morning at a flea market, you are in front of a stall where old cameras and lenses are lined up. On the front ring of the lens you pick up there are lots of numbers and abbreviations in small letters: a millimeter value, a ratio separated by a colon, a circle symbol with a line through it, and an abbreviation of a letter or two. On the side of the body are two small switches, and on the ring a scale in meters and feet.

What do the markings on a lens tell you? Someone who can read these markings knows, before mounting a lens, how wide it sees, how much light it gathers, how close it can focus and what features it has. In this lesson we will learn to read the markings, symbols and switches on lens bodies.

Context

Throughout this module we talked about focal length, maximum aperture, sensor size and lens flaws. Most of this information is written on the lens body, squeezed into a small line. The markings are in a way the lens's ID card, and even though they are written in slightly different ways from manufacturer to manufacturer, the basic information is given with the same logic on almost every lens.

This reading is especially useful when buying a lens second-hand or borrowing a friend's lens. Whether a lens fits your camera, and whether it can do the job you expect, you can often understand by looking at its body. The meaning of manufacturer-specific abbreviations, on the other hand, is always written in that manufacturer's manual and on its website; instead of memorizing them, it is enough to know where to read them.

Simple explanation

How are focal length and maximum aperture written?

On almost every lens, focal length is written in millimeters: on a prime lens a single number, like "50mm"; on a zoom lens a range, like "18-55mm". Maximum aperture, on the other hand, is often written not as "f/1.8" but as "1:1.8". This ratio describes the ratio of the diameter of the lens's opening to the focal length, and is read as f/1.8. On zoom lenses the marking "1:3.5-5.6" says that the lens can open to f/3.5 at its short end, and stays at f/5.6 at its long end; a single number means a constant-aperture zoom. Reading this maximum aperture marking is the first step.

These two pieces of information give the lens's two most important properties. Focal length, together with the camera's sensor size, describes how wide a frame it will give; maximum aperture describes at what shutter speed you can shoot in a room in the evening and how much it can soften the background. When you hold a lens, reading these two pieces of information and converting them to your own camera with the crop factor from Lesson 12.5 shows how it will behave for you.

What do the filter diameter and distance information tell you?

On the lens's front ring, or on the inside of its cap, you see a small circle symbol with a line through it and a number next to it: like "ø58". This is the filter thread diameter in millimeters, that is, the diameter of the filters that screw onto the front of the lens. When buying a filter or a lens hood, you look at this number; a filter of the wrong diameter won't fit the lens.

On many lenses the minimum focus distance is written too: like "0.45m/1.48ft". This is the shortest distance at which the lens can find sharpness, and it is usually measured from the sensor plane. On some lenses a magnification ratio is also given: like "1:4" or "1:1". This ratio describes how large the subject is formed on the sensor, as a fraction of its real size, at the minimum focus distance; 1:1 means the subject is formed on the sensor at its real size, and it is usually seen on macro lenses. The "1:1.8" of maximum aperture and the "1:1" of magnification ratio use the same way of writing, but describe completely different things.

What are switches and abbreviations for?

On the body of many lenses there are small switches. The most common is the switch that changes between autofocus and manual focus; it is usually marked with the letters AF and MF. On stabilized lenses there is a switch that turns stabilization on and off, and on some, a selector for different stabilization modes. Some zoom lenses have a zoom lock so that the lens doesn't extend by itself when pointing down, and some lenses have a limiter switch that makes focus search within a certain distance range.

There are also manufacturer-specific abbreviations on lens bodies. These letters often describe the stabilization system, the kind of focus motor, what size of sensor the lens casts an image to cover, whether it belongs to a professional series, or whether it carries extra protection against dust and moisture. Each manufacturer uses its own letters for this information, and the same letters can mean something different for two manufacturers. That is why, instead of guessing a manufacturer designation, reading the explanation in that manufacturer's manual or on its website is the most reliable way.

What do the markings tell you in a portrait?

The minimum focus distance on the lens body tells you how close you can come to a face; but this doesn't mean you should come that close. Remember the woman in the seaside town: photographed from half a meter, her nose was large; photographed from the far end of the square, her proportions had settled into place. The forty-five centimeters on the body tell you how close you can get to that close frame; they don't tell you that you should get that close for any face, brown or light.

When choosing a lens for a portrait, you convert the focal length on the body for your own sensor, and look at whether it gives the frame you want from the few-meter distance that keeps the face's proportions. The maximum aperture marking, on the other hand, tells you how low you can keep the ISO under an awning or in the corner of a room. That way, a few numbers on the body let you predict in advance both the shape and the light of a portrait.

Visual evidence

You go back to the stall at the flea market. The seller, a brown-skinned old man with thick glasses, hands you the lens. On the front ring it says "50mm 1:1.8" and "ø52"; on the body there is an AF/MF switch and two letters belonging to the manufacturer. The distance scale on the ring starts at "0.45m". You look at the manufacturer's website on your phone and learn that the two letters show the lens was designed for a full-frame sensor.

You mount the lens on your camera and, with the seller's permission, take two frames. In the frame you take from forty-five centimeters, the closest point the lens allows, the lenses of his glasses and the tip of his nose have pushed forward and his ears look pulled back. In the frame you take after stepping back two and a half meters, his face's proportions are usual; the lines creasing around the eyes behind his glasses and the gleam of the old lenses on the stall can be made out. The light of f/1.8 lets you photograph his face at a low ISO in the shade of the awning. A few lines of markings had told you what the lens could do before you even mounted it.

Common mistakes

Summary

The markings on a lens body are its ID card: focal length is written in millimeters, and maximum aperture is often written with a ratio such as "1:1.8" and read as f/1.8; the number next to the "ø" symbol is the filter diameter; the minimum focus distance tells you how close you can come, and the magnification ratio describes how large the subject is formed on the sensor at the closest distance. The switches on the body manage features such as focus and stabilization; manufacturer-specific abbreviations are read from the manual. In a portrait, these markings let you predict in advance the distance that keeps a face's proportions on every skin, and how much light can be gathered in dim light.

Mini assignment

In this assignment you will put together your own lenses' ID cards.

1. Read the focal length, maximum aperture and filter diameter of each lens you have from its body, and write them in a list.
2. If they are given, find and note the minimum focus distance and the magnification ratio.
3. Confirm what the switches on the body are for by trying them on your camera.
4. Research the manufacturer-specific abbreviations on the body in the manufacturer's manual or on its website, and add their meanings to the list.

Check yourself

• Were you able to read each lens's maximum aperture correctly from the "1:" marking?
• Were you able to find the filter diameter and the minimum focus distance?
• For each of your lenses, were you able to add to the list from how many meters you can build a shoulder portrait?

Glossary

Mini quiz

1. What does "1:1.8" written on a lens's front ring describe?

• A) That the magnification ratio is 1:1.8
• B) That the widest aperture the lens can open to is f/1.8
• C) That the filter diameter is 1.8 centimeters
• D) That the lens weighs 1.8 kilograms

2. What does "ø58" written on a lens cap show?

• A) That the filter diameter is 58 millimeters
• B) That the focal length is 58 millimeters
• C) That the minimum focus distance is 58 centimeters
• D) That the lens weighs 58 grams

3. What does a 1:1 magnification ratio on a lens mean?

• A) That the lens is constant-aperture
• B) That the lens shoots in a 1:1 photo format
• C) That at the minimum focus distance the subject is formed on the sensor at its real size
• D) That the lens doesn't magnify at all

4. When shooting a portrait with a 50-millimeter lens whose minimum focus distance is 0.45 meters, what do you do?

• A) Always shoot from the minimum focus distance
• B) Change the filter diameter
• C) Switch the lens to manual focus
• D) Stand a few meters away to keep the face's proportions

Answers

1. B — The ratio on the front of the lens is the ratio of the opening to the focal length, and is read as f/1.8.
2. A — The "ø" symbol shows a diameter; the number next to it is the diameter in millimeters of filters and lens hoods.
3. C — 1:1 describes the subject being formed on the sensor at its real size; it is usually seen on macro lenses.
4. D — The minimum focus distance is the limit of how close you can come; a face's proportions need a distance of a few meters.

Summary card

• Focal length in mm; maximum aperture often as "1:1.8" = f/1.8.
• "ø58" = a 58-millimeter filter diameter.
• Minimum focus distance: the limit of how close you can come; magnification ratio: the size at that distance.
• Switches: AF/MF, stabilization, zoom lock, focus limiter.
• Read manufacturer abbreviations from the manual; in a portrait, on every skin, predict the distance from the markings.

Bridge to the next lesson

On some lens bodies it says "macro" and the magnification ratio reaches 1:1; on some, the front glass bulges outward like a balloon; on some, the body can tilt and slide sideways from its middle. These are lenses designed not for everyday jobs but for particular jobs. What are fisheye, macro and tilt-shift for? The next lesson talks about these special lenses and why they are used in which jobs.