Kayce Photography

Nov5

Though I could explain just about everything to do with digital photography in pure technical jargon, that’d probably defeat the purpose of my site. Below is a list of key terms every photographer needs to know by heart to build his/her foundation on photography technique – written in a manner to help new photographers understand basic fundamentals & choose appropriate cameras/lenses for various applications. If some of my FAQ answers & Digital Photography Resources don’t make complete sense to you, this is for you. More experienced digital shooters can skip this section.

Aperture

Aperture refers to the size of the opening in the lens that determines the amount of light that will hit the camera sensor. The most expensive lenses often feature large maximum apertures (e.g. f/1.2 or f/1.4) & offer the most depth of field control as well as low-light capabilities.

A larger aperture (smaller f-number, e.g. f/2) has a shallow depth of field. Anything behind or in front of the main focus point will appear blurred. A smaller aperture (larger f-number, e.g. f/11) has a greater depth of field. Objects within a certain range behind or in front of the main focus point will also appear sharp.

AI Servo (Autofocus Servo)

Autofocus Servo refers to the camera’s ability to continuously focus on a moving subject, a feature normally only found on digital SLRs. It is generally used by sports or wildlife photographers to keep a moving subject in focus. In “AI Servo” (Canon) or “Continuous” (Nikon) mode, the camera will continue to focus based on its own focus rules (and your settings) while the shutter release is half-pressed or fully depressed (actually taking shots).

Canon Lens Mounts (EF vs EF-S)

Canon’s EF designation stands for lenses mounted with “Electronic Focus” – handled by a dedicated electric motor built into the lens. In 2003, Canon introduced a subset of EF-S lenses specifically for digital EOS cameras with a 1.6x crop (ASP-C sensor DSLRs). EF lenses can be mounted on EF-S bodies, albeit with cropped image, while EF-S lenses cannot be mounted on EF (full-frame) bodies.

Chromatic Aberration (CA)

Chromatic aberration refers to colour “fringing” (usually purple or green) that appears in high-contrast areas of an image (e.g. branches against a bright sky), generally around the edges of the image frame. Simply put, the less CA a lens produces, the better – newer, high-quality lenses aim to reduce CA with low-dispersion glass.

Distortion (Barrel vs Pincushion)

Barrel distortion happens most frequently with wide-angle lenses, causing an image (noticeable with straight lines) to become rounded or “inflated” – especially with subjects near the edge of the image frame. Pincushion distortion refers to the opposite, causing images to become pinched at the center. Obviously, the less distortion a lens has, the better the image it will produce, especially important with commercial formats such as architecture, portrait & product photography.

Depth of Field (DOF)

Depth of field (DOF) refers to the areas of the photograph both in front and behind the main focus point which remain “sharp” (in focus). Depth of field is affected by the aperture, subject distance, and focal length.

A larger aperture (smaller f-number, e.g. f/2) has a shallow depth of field. Anything behind or in front of the main focus point will appear blurred. A smaller aperture (larger f-number, e.g. f/11) has a greater depth of field. Objects within a certain range behind or in front of the main focus point will also appear sharp.

Coming closer to the subject (reducing subject distance) will reduce depth of field, while moving away from the subject will increase depth of field. Lenses with shorter focal lengths produce images with larger DOF. For instance, a 28mm lens at f/5.6 produces images with a greater depth of field than a 70mm lens at the same aperture.

Dynamic Range

I’m simplifying, but the more dynamic range a camera sensor has the better the sensor is. In practical terms, cameras with a large dynamic range are able to capture shadow detail and highlight detail at the same time without clipping (e.g. details in a bright blue sky being lost on a sunny day).

Focal Length

The focal length of a lens is defined as the distance in millimetres from the optical center of the lens to the focal point, which is located on the sensor or film if the subject (at infinity) is in focus. The camera lens projects part of the scene onto the sensor or film. The field of view (FOV) is determined by the angle of view from the lens out to the scene; larger full-frame sensors have wider FOVs and can capture more of the scene. The FOV associated with a focal length is based on 35mm film photography, given the popularity of this format over other formats. Lenses with a focal length of 50mm are called “normal” because they work without reduction or magnification and create images the way we see the scene with our naked eyes (same picture angle of 46°).

Resolution

The resolution of a digital image is defined as the number of pixels it contains. A 5 megapixel image is typically 2,560 pixels wide and 1,920 pixels high and has a resolution of 4,915,200 pixels, rounded off to 5 million pixels. Sensor resolution refers to the number of effective pixels located on a DSLR sensor.

Sensor Sizes (Full-Frame vs Crop-Sensors)

Deriving its size from the popular 35mm film camera days, a full-frame DSLR sensor measures roughly 36x24mm, whereas a “crop-sensor” or ASP-C sensor measures around 25×16.7mm, creating a focal length multiplier effect of 1.6 (e.g. 50mm lens used with an ASP-C camera effectively becomes an 80mm lens) on Canon sub-frame DSLRs such as the EOS Rebels, EOS 10D-60D & EOS 7D. Full-frame sensors offer more depth of field control, generally higher dynamic range as well as better noise control, but also cost considerably more to manufacture than their crop-sensor counterparts found on lower-end DSLR bodies. Canon’s crop-sensor DSLRs are also uniquely compatible with EF-S mount lenses, designed specifically to make optimal use of the smaller sensors.

Vignetting

Vignetting refers to the visible darkening of image corners, usually found in photos taken by lower end zoom lenses. While this is sometimes a preferred effect in a photo, lenses that feature less vignetting are regarded as having better optical quality due to less-compromised images.

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