What is…? – Terms, Abbreviations and Lens Designations

Terms, Abbreviations and Lens Designations

Everyone who takes a deeper dive into photography for the first time, gets drowned by a flood of strange terms and abbreviations. Test reviews, tutorials, and online communities are just full of them. What confused me even more in the beginning, was the fact that there is often more than one designation for the same thing – or, vice versa, one and the same shortcut has several different meanings. I am currently replacing some of my gear, so I had to make sure I was adding the correct designations to the respective item descriptions. And since I was at it anyway, I’m writing it down here for future reference – yours, as well as mine.


Photography fills an abundance of books and videos, which describe the basic steps, give instructions, and explain the terminology. I do not intend to compete with that. However, I do want to give an explanation in my own words of the terms I am using regularly in my blog posts.

For most of the terms, I have added links to the respective articles on Wikipedia, in case you want to read more about a certain topic. And if you’re interested in all the details, I highly recommend Mark Levoy’s “Lectures on Digital Photography”.


From a technical point of view, the aperture is the opening in the lens through which light hits the sensor. Usually, it can be varied in size (⇒ Wikipedia).

From an artistic point of view, the aperture is the most important tool for creating an image. It controls the depth of field, i.e. the distance range that will be shown sharp in the picture. This makes the difference between a portrait with a soft background, and a landscape photo where the entire frame is in focus. It also influences the amount of light passing through the lens, in particular when using a flash.

  • The aperture setting is always given in relation to the lens. The aperture value is calculated by dividing the focal length of the lens by the diameter of the effective opening. As the size of the opening is the denominator of this fraction, it means that the aperture value is the smaller the larger the opening is.
  • The aperture values are set so that switching from one value to the next always corresponds to either doubling or halving the amount of light let through. This is equal to doubling or halving the size (area) of the aperture opening. The area of a circle with radius r is generally known to be π * r². If I want to double that area, that means: 2 * π * r² = π * 2 * r² = π * (√2)² * r² = π * (√2 * r)². Hence, you need to change the radius by a factor of  √2 ≈ 1.4, if you want to double the area.
  • Thus, the aperture values are always multiples of √2: ƒ/1, ƒ/1.4, ƒ/2, ƒ/2.8, ƒ/4, ƒ/5.6, ƒ/8, ƒ/11, ƒ/16…
Lens with aperture set to different values for comparison (Source: Wikipedia)
  • Since on manual lenses, the aperture ring clicks into place at each of these values, they are also referred to as ‘stops’. Accordingly, the terms ‘stop of light’, ‘stop up’ and ‘stop down’ all relate to doubling or halving the amount of captured light. These phrases are used even if the effect is not achieved by changing the aperture, but by other means, such as changing the exposure time, ISO value, or flash output.
  • Between these ‘full’ values, there are usually values for ±⅓ stop, i.e.: ƒ/2.8, ƒ/3.2, ƒ/3.5, ƒ/4.
  • This notation makes the aperture value, respectively its effect on the exposure of the image, independent from the lens and camera used. Consequently, an image taken of a particular subject and correctly exposed at ‘ISO 100, ƒ/8, 1/200th sec.’ will be correctly exposed with every camera, regardless of size and brand, on which I can dial in these settings. What will be different, though, depending on focal length and sensor size, are the field of view, the angle of view, and the depth of field.
  • When mixing ambient light and flash, the aperture controls the amount of light from the flash in the image, while the ambient light is controlled by the shutter speed.

The term is derived from the Japanese word for “blurred”. In photography, it describes the quality of the out-of-focus areas in a picture taken with a wide-open aperture (⇒ Wikipedia). The bokeh depends on the construction of the respective lens, and the quality of the individual lenses it is comprised of. In particular, portrait lenses usually produce a nice bokeh, to create smooth backgrounds that do not distract in any way from the subject. There are, however, lenses that produce a rather fidgety bokeh, for instance because contours get doubled in out-of-focus areas.

Chromatic Aberration /
Color Fringing

When light passes through drops of water, the individual colors are refracted differently. Sunlight gets split into its individual colors, which we see as a rainbow. The same happens when light passes through pieces of glass in a lens. This means the individual lenses need to be tuned in a very specific way to ensure that on the camera sensor, all the different colors match up again in the intended way. Where this fails, green and purple color fringes appear on contrasting edges in the image, for instance at branches of a tree against a bright sky, or the white frame of an otherwise dark window (⇒ Wikipedia). Chromatic aberration can be corrected in many image-processing software tools, such as Adobe Lightroom.

Crop Factor

To be able to compare different camera types, the main parameters such as the focal length are always converted to the so-called full-frame format. This designation applies to cameras with a sensor the same size as a negative of a 35 mm miniature film (24 x 36 mm). The crop factor equals the ratio of the length of the diagonals (⇒ Wikipedia).

  • Popular formats include APS-C (crop factor 1.5 (Nikon) or 1.6 (Canon)) and Micro-Four-Thirds (crop factor 2 (Olympus, Panasonic)).
  • To compare focal lengths, the values are multiplied by the crop factor: 50 mm on a Canon APS-C camera thus equal – times 1.6 – 80 mm on a full-frame camera. This correspondence applies only to the field of view, however, and not to the angle of view.
  • To compare depth of field, the aperture also gets multiplied by the crop factor. The rear camera on Apple’s iPhone 7, for instance, has an aperture of ƒ/1.8 and a crop factor of 7.2. This roughly equals ƒ/13 on a full-frame camera, which makes it clear why it is almost impossible to get pictures with a blurred-out background using a cell phone camera (large aperture number = large depth of field).
Depth of Field

Depth of field refers to the distance range, within which objects are shown sufficiently sharp in the image (⇒ Wikipedia).

  • In principle, only objects exactly in the focus plane are shown 100% sharp on the image.
  • The further something is away from the focus plane, either in front of it or behind it, the more blurred it becomes. This is a gradual transition, and where an object is still “sharp enough” depends on the resolution of the camera as well as the eye of the beholder.
  • Depth of field is controlled by three factors:
    1. The aperture: low aperture number = shallow depth of field; larger aperture number = large depth of field.
    2. The focal length: the shorter the focal length, the larger the depth of field.
    3. The focus distance: the further away the subject is, the larger the depth of field. Beyond a certain focus distance (depending on focal length and aperture), the depth of field becomes infinite. This distance is called the hyper-focal distance.
  • For this reason, portraits are usually taken with a long focal length and wide-open aperture. Thus, only the face is in focus, while the background becomes as blurred as possible. For landscape pictures, on the other hand, usually a short focal length is used, together with a medium or narrow aperture (such as ƒ/8), to get as much of the picture in focus as possible.
Exposure Triangle

Illustrates the correlation of shutter speed, aperture, and ISO setting for the correct exposure of an image.

  • Each of the three parameters has an exposure component and an artistic component:
    • Each component can make the image darker (fast shutter speed, narrow aperture, low ISO) or brighter (slow shutter speed, wide aperture, high ISO)
    • The shutter speed can either freeze motion (fast) or show motion (slow)
    • A wide-open aperture creates a shallow depth of field, so only the subject is in focus, while a narrow aperture results in a large depth of field, where most of the image is in focus
    • Low ISO values create a clean image, while high ISO values will cause a noisy (grainy) image
    • Depending on the type of photo you want to take, you set one or two of them depending on your priorities, and let the camera figure out the rest.
    • The blog ‘Hamburger Fotospots‘ offers a great cheat card, which illustrates the three parameters listed above, along with their respective effects. The web page is in German, but the ZIP package you can download includes an English version of the cheat card:
Source: Hamburger Fotospots
  • First example: If I cut the exposure time in half, but double the ISO setting, the exposure stays the same (motion blur is reduced, but the picture quality decreases)
  • Second example: If I change the aperture from ƒ/2.8 to ƒ/5.6, I can quadruple the exposure time without changing the exposure (motion becomes more visible, but the depth of field is changed, too).
  • All theory is grey, so here are two YouTube videos that illustrate this very well:
Exposure Time /
Shutter Speed

The time interval during which light hits the sensor. Most cameras allow adjustment between 1/4,000th of a second and 30 seconds (⇒ Wikipedia).

  • Higher-range camera also offer 1/8,000th of a second
  • For long exposure times beyond 30 seconds, there is the so-called ‘bulb’ mode, where the shutter is controlled manually by either pressing and releasing the shutter button, or by pressing it twice.
  • See below for more information about the shutter.
Flash Sync Speed Identifies the shortest exposure time at which a flash without special ‘high speed’ capability will render a fully exposed image. This depends on the build of the shutter (see below), but with most cameras, it is around 1/200th of a second.
Internal Focus On a lens with internal focusing, all moving elements for focusing on your subject are inside the lens. This means that in particular the front element of the lens does neither extend nor rotate when focusing. This is important when using filters that depend on the correct orientation to get the desired effect, such as polarizing filters or graduated filters.

The name of the International Organization for Standardization in Switzerland. As the shortcut for this organization would be different in every language (in English, it should actually be IOS), ISO is used as a proper name. It is derived from the Greek syllable “iso”, meaning “equal”. In photography, the ISO value describes how sensitive an analog film or digital sensor is to light, as defined in the standard ISO 5800 (⇒ Wikipedia).

  • The default value with most cameras nowadays is ISO 100.
  • The higher the ISO value, the more sensitive to light the film or sensor is. This goes along with an increasing reduction of image quality by increased grain or noise. How strong this effect is on digital cameras depends on the build of the sensor, in particular the size of each individual pixel – the larger, the better. This is why low-light cameras usually have low resolution.
Minimum Focus Distance

The minimum focus distance is the shortest distance on which the camera can still focus with the respective lens. It is important to know that this distance is always measured from the sensor, and not from the front element of the lens. The position of the sensor is marked by a symbol (0) on the camera body. If it is given e.g. as 5 inches, but the distance from the sensor to the front element is already 4 inches, then there is just 1 inch of space left to the targeted object. In general, the minimum focus distance increases with the focal length; for telephoto lenses it can easily be 5 ft. or more. Macro lenses are an exception, because they are built specifically to focus at very short distances, to achieve the large magnification.


The shutter is a mechanism inside the camera that allows light to hit the sensor only for the chosen exposure time (⇒ Wikipedia). There are two main types of shutters:

  • An electronic or digital shutter actually isn’t a shutter in the original sense, because light is hitting the sensor all the time. The sensor gets reset (all values set to zero), and after the given time, the values of all pixels are read out. The advantage is that this happens completely silent, as there are no moving parts. Most video, cell phone, and compact cameras work this way, as well as DSLRs in video mode.
  • SLRs usually have a mechanical focal-plane shutter, which allows for very precisely controlled exposure times, as short as 1/8,000th of a second. It is usually built as a pair of two curtains. At the beginning of the exposure time, the first curtain, which until then had completely covered the sensor, slides away. At the end of the exposure time, the second curtain moves out of its resting position, follows the first curtain, and covers the sensor again. At higher shutter speeds (less than 1/200th of a second), the two curtains move so close to each other, that at no point in time the entire sensor is exposed at once. Instead, a slot moves across the sensor so that every region of the sensor gets exposed for the chosen time interval.
    • This slow-motion video on YouTube shows very well what happens inside a camera when taking a picture.
    • Due to the way the shutter works, flashes need a special ‘high-speed synchronization’ mode for working with fast shutter speeds. Otherwise, a black bar would be visible in the image, because only that part of the sensor that was visible between the two shutter curtains when the flash fired, was exposed.
    • Design and way of working of the shutter also explain the terms ‘first / second curtain‘ for firing the flash at the beginning or at the end of the exposure time.
  • Both shutter types do not capture the entire image at once, but the exposure rather moves across the frame. This caused by reading out the pixels row by row with an electronic shutter, or by the movement of the curtains of a focal-plane shutter. The downside is that fast moving objects become distorted in the final image (so-called ‘rolling shutter effect‘). There are also cameras with a so-called ‘global shutter’, which capture the information of the entire image at once. This technology is typically used in rather expensive high-speed cameras.
  • Robert Hall has a video on YouTube where explains the differences as well as the pros and cons of the two shutter types.


There are an almost infinite amount of abbreviations in photography. I have selected the ones I often use myself. This section leaves aside all abbreviations that designate lens characteristics; you will find those below in a table of their own.


Auto-focus – The system your camera uses to focus on the targeted subject. There are two distinctly different auto-focus systems: Phase detection is what single-lens reflex cameras employ when using the optical viewfinder. Edge detection is applied when looking through an electronic viewfinder or using the display, for instance on a cell phone. Phase detection is faster, while edge detection is more reliable. In addition, depending on your camera and lens, there are different types of drives moving the lenses accordingly; also see the lens designations below.


Advanced Photo Systems-Classic – This designation embraces digital cameras with a sensor size between 22.5 x 15.0 mm (crop factor 1.6) and 25.1 x 16.7 mm (crop factor 1.5). Basically all interchangeable lens cameras with a retail price under 1,000 € have such a sensor. APS-C is not a standardized label; the actual sensor size varies between manufacturers. Nikon calls their APS-C cameras “DX”.

The designation goes back to the APS system, which was invented back in the 1990s for analog film. The image size is about ⅓ of a 35 mm miniature film. This made it possible to build much smaller cameras, and to store additional information on the film. Due to the quickly emerging digital photography, however, APS never became accepted for analog film, and quickly vanished again.

APS-C as a classification of the sensor size is not related to the camera sensor technology APS (Active Pixel Sensor). This is a type of so-called CMOS sensor, which, due to their compact build and low energy consumption, are used in almost all cell phones and compact cameras.

ILC Interchangeable Lens Camera – A camera where you can quickly change the lens. Often used as a generic term for mirrorless or single-lens reflex cameras, to distinguish them from compact cameras with a built-in lens.
DSLM Digital Single-Lens Mirrorless – Digital cameras without optical viewfinder. They are often also referred to a System Cameras (Example: Sony Alpha a6000). “Single-Lens” means that the image in the viewfinder is captured through the same lens as the actual photo. On older compact cameras, the viewfinder often had its own optics. Nowadays, basically all cameras are digital, the D is often omitted and just SLM is being used. In addition, there are several synonymous acronyms: MILC (Mirrorless Interchangeable Lens Camera), MSC (Mirrorless System Camers) and – my favorite  :mrgreen: – EVIL (Electronic Viewfinder Interchangeable Lens camera).
DSLR Digital Single-Lens Reflex – Digital cameras with an optical viewfinder that uses the same lens as the image sensor (Example: Canon EOS 760D). Again, the D is often omitted and just SLR is used.
MF Manual Focus – Interchangeable lenses usually allow for manually focusing on your subject. This is meaningful in difficult lighting conditions, e.g. for night photography, or for pictures where a moving object shall be captured in a certain position and the auto-focus wouldn’t be fast enough.

Micro-Four-Thirds – A sensor format with crop factor 2, used primarily by Olympus and Panasonic. “Four Thirds” relates to the 4:3 aspect ratio of the sensor, in contrast to the otherwise usually 3:2.


Straight Out Of Camera – This abbreviation is mostly used in online forums and photo communities, and means that the picture it refers to has not been post-processed on a computer in any way.


Acronyms on lenses tend to be especially confusing, because the manufacturers use different labels for the same functionalities and characteristics.  The table below summarizes the most prevalent shortcuts for the brands I use.

I have left out all terms related to the ‘optical formula’ of a lens, i.e., which specially shaped lenses are built in, and which specific coatings they have. This would go far beyond the scope of this post. In the end, all that matters it their effect on the image quality (distortion, flaring, and chromatic aberration).

Function Canon Samyang Sigma Tamron Tokina
Lens for Full-frame Cameras EF DG Di FX
Lens for Cameras with APS-C Sensor EF-S CS DC Di II DX
Lens for mirrorless Cameras EF-M FE (Sony E-Mount) DN
Image Stabilizer IS (Image Stabilization) OS (Optical Stabilizer) VC (Vibration Compensation)
Auto-focus USM (Ultra-Sonic Motor)

STM (Stepping Motor)

 AF HSM (Hyper-Sonic Motor) USD (Ultrasonic Silent Drive)  AF
Internal Focus IF IF IF IF
Professional Lens L (Luxury) A (Art)

S (Sport)

EX (Excellence)

SP (Super Professional) AT-X Pro
Consumer Lenses C (Contemporary) AT-X
  • Canon: Lenses with internal focus, as well as consumer lenses, do not have a dedicated designation.
  • Samyang: Lenses from Samyang are sold under several different brands, including Rokinon, Bower, Opteka, Pro-Optic, Vivitar und Walimex. They are technically identical, but their prices vary drastically. Full-frame lenses do not have a special label. No lenses with image stabilization are available. Finally, Samyang does not distinguish between different product lines.
  • Tamron: As far as I know, Tamron does not offer any lenses for mirrorless cameras. Consumer lenses do not have a specific label.
  • Tokina: There are no lenses available with image stabilization, or for mirrorless cameras.


Recommendation: When you get started, all those terms and abbreviations seem rather confusing. But don’t let yourself be scared by that! To learn the basic terms in the beginning, a book can really help; but in the end, it’s ‘learning by doing’. In particular, the exposure triangle needs closer attention, and you’ll need to memorize the creative possibilities (How do I blur the background? How do I freeze motion?).

What I’ve learned: A lot  😀 And I’m still learning. Even writing this article helped me to better understand a number of things…


In addition to the Wikipedia links, additional information can be found here:

Picture credits: Title image: own graphic.

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