Your Digital Photography Glossary

Decipher Photographic Lingo & Jargon

For those inclined to want more detail, links to corresponding Wikipedia and other reference pages will fill in origins and technical details behind the terms.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Aperture

The opening in the lens that admits light to the camera sensor. The size of the aperture is controlled by a diaphragm that operates much as the iris of the eye. As aperture decreases, depth of field increases, but the amount of light reaching the sensor decreases.

Most commonly, aperture refers to the ratio of the focal length of the lens to the diameter of the lens opening. For that reason, you will usually see an aperture setting written in the form of an f-number, or f-stop, as in f/16. In that example, the aperture diameter is 1/16 of the focal length of the lens.

The amount of light that reaches the sensor varies by the square of the f-number (because the area of a circle is related to the square of the diameter). For this reason, f-numbers that vary by a factor of 1.4 (the square root of 2) increase or decrease the amount of light by a factor of 2.

f-numbers of 1.2, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, and 32 each admit approximately one-half the light of the smaller f-number, with the benefit of increasing depth of field.

Aperture Priority Exposure Mode

This exposure mode allows the user to specify which aperture setting to use for all photographs made while in this mode. The camera will use the selected aperture and select an appropriate shutter speed to give the best exposure.

Aperture priority mode allows the user to control depth of field. The trade-off to watch for is that the camera may select a shutter speed that is too slow, either in terms of camera shake (if hand-holding the camera) or motion blur (if the subject is moving).

One of several exposure modes offered by most digital cameras, and typically found on a camera dial indicated with the letter 'A'

Aspect Ratio

For images, aspect ratio refers to the ratio of width to height, although it is sometimes more loosely interpreted as the ratio of the longest dimension to the shortest.

Common aspect ratios in photography are:

• 4:3 -- for standard monitors and many digital cameras
  
  
• 3:2 -- for some DSLR's, for 35mm cameras, and for standard 4: x 6" prints in the US.
  

For more detail on aspect ratios, maybe more than you ever thought you wanted to know, see the Guidelines for Cropping Photos.

See also Golden Ratio.

Auto focus

Digital cameras employ an automatic system for precisely focusing the lens on your photo subject.  These auto focus systems include active infrared-based systems as well as passive "phase-detect" and "contrast-detect" systems.

For more perspective on auto focus, see Photo Sharpness: Focus Your Camera

Top

B

Big Glass or Big Guns

Colloquial terms referring to long telephoto lenses, typically of focal lengths starting at 400 mm or 500 mm, such as those used for sporting events or wildlife photography. See also Glass.

Bokeh

A term describing quality of the out-of-focus areas of a photograph, which may vary from a milky-smooth texture to coarse artifacts that distract the eye from the photo's subject. This is especially important when working with shallow depth of field, when the out of focus background is intended to offset the crisp focus of the subject.

Photographers use bokeh as a term to describe the quality of a lens, where smoother bokeh is better.

For examples, see Photo Sharpness: Focus.

Check Wikipedia for a technical overview and origins of the word.

Top

C

Chimping

The act of previewing your photos with your camera's LCD after nearly every shot. Seen by some as cheating and the mark of an amateur, the word often has a negative context. But, proponents see chimping as a way to ensure that you get the best possible picture.

You decide what works best for you. Check out the origins of chimping and learn about its pros and cons at Wikipedia.

Circle of Confusion

When a point of light is not perfectly focused on the image sensor, it creates a spot known as the circle of confusion. An image will appear in focus when the circle is smaller than the eye can resolve.  Also know as blur circle.

For more detail, see Photo Sharpness: Focus.

Continuous-Servo Auto focus

Continuous-servo auto focus systems activate when the shutter release button is pressed half-way down.  If the subject moves, the auto focus system will adjust the focus distance, and will continue adjusting as long as the subject continues to move.

See also, Single-Servo Auto focus.

For more detail, see Photo Sharpness: Focus Your Camera.

Crop Factor

A term introduced with the advent of digital photography to explain the relationship of lens focal length to sensor size. With 35 mm film SLR's, we learned to associate focal lengths with a specific magnification or widening of an image. A 50 mm lens was considered "normal" as it covered a field of view (FOV) approximately equal to that of the human eye when captured by the standard, full-size 36 mm x 24 mm film frame.

Digital sensors, until recently, have all been smaller than the "full-size" 35 mm standard, with the result that the FOV for a given lens is smaller. A smaller field of view corresponds to a longer focal length. This is of great advantage for telephoto shooting, but works against the effect of wide angle lenses by also narrowing their field of view.

Crop factors vary by camera manufacturer and camera model. Some typical examples are:

• 1.6x - Canon EF-S (ex. Canon EOS 7D)
• 1.5x - Nikon DX (ex. Nikon D300 @ 23.6 mm x 15.8 mm)
• 1.3x - Leica M8

Top

D

Depth of Field

Refers to the range of subject matter that appears to be in focus in an image. Although only one plane in a photograph can be in precise focus, planes both beyond and in front of the focus distance may appear to be in focus. As the lens aperture decreases in diameter, the depth of field increases.

For examples, see Photo Sharpness: Focus Concepts and Depth of Field.

DSLR

Digital Single Lens Reflex. Refers to a digital camera characterized by have interchangeable lenses and a viewfinder that looks directly through the lens via a special prism and mirror arrangement.

See also SLR.

Top

E

EXIF

Exchangeable Image File Format. Refers to that part of a digital image file which describes the properties of a photograph, including information about exposure settings, date, camera and lens specifications, dimensions, flash use, and related information. Most image viewers and editors display this information, which can be a valuable aid in learning to improve your digital photography.

Exposure

An indication of how much light is made available to the image sensor when depressing the shutter release button. The amount of light is controlled by shutter speed and aperture. In common usage, the ISO setting is given as part of the exposure settings as a way to factor in the sensitivity of the sensor.

Example: 1/200 second, f/8, ISO 400

Exposure Mode

The camera's exposure mode, usually set with a dial, tells the camera whether aperture or shutter speed are set manually by the user or automatically by the camera to achieve the best exposure. Typically, there are four settings, each indicated by a single letter:

P = Programmed Mode (camera sets both aperture and speed)
A = Aperture Priority Mode (user sets aperture, camera sets speed)
S = Shutter Priority Mode (user sets speed, camera sets aperture)
M = Manual Mode (user sets shutter speed and priority)

Exposure Equivalents

Exposure settings are considered equivalent when the image sensor is able to produce alternative images of the same scene with equal brightness. If you adjust one element in the triad of shutter speed, aperture, and ISO by one stop, you must make a compensating negative adjustment of one stop in another element in the triad.

For example, if you halve your shutter speed you increase exposure by one stop. This is because the slower speed, say 1/30s vs. 1/60s, lets light hit the sensor for twice as long. To achieve equivalent exposure, you must compensate by either decreasing the aperture by one stop (say from f/5.6 to f/8) or by decreasing the ISO setting by one stop (say from 400 to 200).

For a table of exposure equivalents, see Photography Exposure.

Exposure Value

Exposure value, usually abbreviated as "EV", refers to an exposure defined by combinations of aperture and shutter speed that produce the same exposure for a given ISO setting. While there is a mathematical formula for determining an exposure value number (a positive or negative integer) for specific settings, EV is usually used as a relative term to describe equivalent exposure setting combinations. One step in exposure value is equivalent to one stop.

Example 1: 1/200 sec, f/8 has the same EV as 1/400 sec, f/5.6, as both combinations allow the same amount of light to the image sensor.

Example 2: 1/100 sec, f/8 is one EV greater than 1/200 sec, f/8. The slower shutter speed lets twice as much light hit the sensor.

Top

F

Focal Length

Measure of the distance, in millimeters, from the optical center of the lens (when focused at infinity) to the focal plane (the face of the digital photography sensor). Longer focal lengths found in telephoto lenses take in a narrow field of view, making distant objects appear closer and larger. Shorter focal lengths take in a wider field of view and make objects appear farther away and larger.

If you are mathematically inclined, check Wikipedia for a deep mathematical overview of optics and focal length.

Focus

The property of an image which defines how sharp, or clearly-defined, the photographic subject appears.

For more details, see Photo Sharpness: Focus.

f-stop

A number indicating the size of the lens aperture.

See also the more generic term, stop.

Top

G

Glass

A colloquial term referring to interchangeable lenses, since glass is the most important element inside lenses. "Big glass" and "big guns" refer to long telephoto lens.

Golden Ratio (or Golden Rectangle)

A ratio of image width to height that is considered well-balanced and pleasing to the eye.

For rectangular images, this is an aspect ratio of very nearly 1.618:1.

In text, this is described as the condition where the ratio of one number to another is the same as the ratio of the largest of those numbers to the sum of the numbers. That is, if b is the larger of the two numbers:

     a:b = b:(a + b)

For a more complete description, see this Wikipedia definition.

Grab Shot

Photograph taken quickly to capture the moment, without special consideration of overall photo composition or quality. Often, grab shots are incidental to the purpose of a photo session, such as pictures of wildlife wandering through an outdoor photo shoot.

Top

I

Image Stabilization

Image stabilization is a technology for reducing the impact of camera shake on images. By compensating for camera motion, image stabilization allows for slower shutter speeds without introducing blur into photographs. Generally, photographers can expect between two and four stops of acceptable shutter speed reduction.

For more detail, including the brand names used by various camera manufacturers for this technology, see the Image Stabilization page.

ISO

A measure of the sensitivity of a camera's image sensor. Higher ISO numbers indicate higher sensitivity, with each doubling of ISO equal to one stop.

Generally, an increase in ISO also increase the amount of noise in an image, although the upper limit of relatively noise-free ("clean") ISO's increases from year to year. For example, in 2005, a typical clean ISO would be in the range from 200 to 400. In 2010, clean ISO's of 6400 can be found on higher-end DSLR's that reach noisy ISO's of 102400 for extreme low-light photography. However, the cleanest ISO's are found at the low end of the range, typically 100 or 200.

From International Organization for Standardization standard ISO 5800:1987, for camera film speed. ISO ratings for film and digital cameras are equivalent.

Top

 

J

JPEG

The most common digital photography image file storage format. Indicated in filenames with the extension .JPG. JPEG is a "lossy" compressed file format, meaning that it does not keep all image data - you select how much data to retain through camera and image editor settings that allow you to trade image quality for smaller file size. The higher the quality, the larger the file size. The Joint Photographic Experts Group created this standard.

Top

 

M

Macro Lens

A lens used for close-up photography that reproduces subjects at a ratio of approximately 1:1 or larger on the image sensor. Both prime and zoom lenses may operate as macro lenses at the close end of their focusing range.

Macro Mode

On point-and-shoot cameras, a setting that allows the lens to focus on objects only a few inches or centimeters away, allowing for higher magnification ratios approaching 1:1.

Manual Exposure Mode

This exposure mode gives the photographer the most control over exposure, by allowing her to specify both the shutter speed and aperture to use for all photographs made while in this mode.

Manual mode allows the user to select the balance between depth of field and motion (camera shake, freezing of moving subjects, and motion blur). It is then fully up to the photographer to select the exposure settings that will deliver proper exposure.

One of several exposure modes offered by most digital cameras, and typically found on a camera dial indicated with the letter 'M'

Top

O

Optical Stabilization

Sigma's branding of its image stabilization technology.

See the term Image Stabilization.

Top

P

Prime Lens

A lens with a fixed focal length.  As opposed to a zoom lens with a variable focal length.  Prime lenses are easier to construct and generally use fewer lens elements that zoom lenses, so they usually have better optics for lower cost.

Programmed Exposure Mode

This exposure mode gives the photographer the least control over exposure, as the camera makes the choice of both aperture and shutter speed based upon its best assessment of lighting conditions.

This mode is useful for taking snapshots or in situations where there is not sufficient time to work with the other, more interactive, exposure modes.

One of several exposure modes offered by most digital cameras, and typically found on a camera dial indicated with the letter 'P'.

Top

S

Shake Reduction

Pentax's branding of its image stabilization technology.

See the term Image Stabilization.

Shutter Priority Exposure Mode

This exposure mode allows the user to specify which shutter speed to use for all photographs made while in this mode. The camera will use the selected speed and select an appropriate aperture to give the best exposure.

Shutter priority mode allows the user to control camera shake, freezing of moving subjects, and motion blur. Because the camera varies aperture to obtain the best exposure, depth of field will also vary with the camera's decisions.

One of several exposure modes offered by most digital cameras, and typically found on a camera dial indicated with the letter 'S'

Shutter Speed

A measure of the amount of time that the shutter exposes the image sensor to light, expressed in seconds and fractions of seconds. For example, typical shutter speeds include 4, 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, and 1/125 seconds, although the range goes much slower and much faster. A range of 30 seconds to 1/8000 second is not uncommon. Note that in the series above, each shutter speed was approximately twice as fast (one stop faster) than the previous shutter speed.

Single-Servo Auto focus

Single-servo auto focus systems activate when the shutter release button is pressed half-way down.  The system holds that focus position as long as the shutter release button is held down.

See also, Continuous-Servo Auto focus.
For more detail, see Photo Sharpness: Focus Your Camera.

SLR

Single Lens Reflex. A type of camera that uses a mirror in front of the focal plane (film or digital image sensor) to direct the image through a viewfinder mounted above the axis of the lens. This allows the photographer to view the image exactly as it will be received by the sensor or film. The mirror instantly flips up and out of the way for the duration of the exposure when the photographer presses the shutter release. SLR cameras support advanced functionality, most notably interchangeable lenses, but also advanced focus, metering, and flash systems, as well as fast repetitive shooting rates.

A digital SLR is usually referred to as a DSLR.

Stop

A relative measure of light that will hit the image sensor during exposure, commonly used to indicate changes from a known exposure as in to "take it down one stop" to lessen the exposure.

One stop indicates a halving or doubling of the exposure by adjustments to aperture, shutter speed, or ISO.

See also the more specific term, f-stop.

Top

T

Tack Sharp

Images that are precisely in focus and free from motion blur are said to be "tack sharp".  This is similar to the expression of mental acuity, "sharp as a tack".

Sharpness is one of the three key elements of CSE, the main skills required for excellent digital photography. Read more about tack sharpness here.

Telephoto Lens

A lens that has a narrower field of view than normal human vision. In photographer's terms, this is a lens with a 35 mm-equivalent focal length of greater than 50 mm, or an angle of view less than 46°.

Typical telephoto prime lenses start at 85 mm, ranging up to expensive 1200 mm monsters. A common telephoto lens is 200 mm, with 12° angle of view on a full-frame 35 mm sensor. That narrows to an 8° angle of view on a Nikon DX sensor that is 2/3 the size of a full-frame sensor.

You can see that the crop factor of less-than-full-frame digital sensors increase the "reach" of telephoto lenses by reducing the angle of view.

TIFF

Tagged Image File Format. A flexible image file format originally used for scanning of black and white images. Now expanded to support high-resolution digital color images, TIFF is generally used to retain maximum image quality. TIFF files are much larger than the lower quality JPEG files, and are most often used as a portable format for highest quality image editing.

Top

V

Vibration Reduction

Nikon's branding of its image stabilization technology.

See the term Image Stabilization.

Top

W

Wide Angle Lens

A lens that has a wider field of view than normal human vision. In photographer's terms, this is a lens with a 35 mm-equivalent focal length of less than 50 mm.

Typical wide-angle prime lenses start at 35 mm, ranging down to 10 mm or less. A common wide angle lens is 20 mm, with 94° angle of view on a full-frame 35 mm sensor. That narrows to about 70° on a Nikon DX sensor that is 2/3 the size of a full-frame sensor.

Unlike with telephoto lenses, where the crop factor improves the "reach" of the lens, with wide angle lenses, the crop factor's increased reach works against the objective of getting the widest possible angle of view.

Top

Z

Zoom Lens

A lens with a variable focal length (e.g. 18 - 55 mm or 70 - 200 mm).  Zoom lenses provide more compositional flexibility because they allow the photographer to change the angle of view exposed to the image sensor, giving the sense of moving closer or further from the subject.  Zoom lenses of recent years have achieved very good optical qualities, but are more complex and generally more expensive than prime lenses.

Top

---

Return from Digital Photography Glossary to Home