Comparison - Lenses

This glossary gathers the terms you will come across in the lens comparison. Every acronym is spelled out when its meaning is known. Some are simply trade names (Art, GM): they denote a range rather than an abbreviated word.

Reading a lens name

Take Sony FE 70-200mm f/2.8 GM OSS II:

• Sony - The brand.
• FE - Full-frame E-mount.
• 70-200mm - The zoom's focal range, from 70 to 200 millimetres.
• f/2.8 - The maximum aperture.
• GM - G Master, Sony's high-end range.
• OSS - Optical SteadyShot, the lens's optical stabilisation.
• II - The second generation of this lens.

Mount and compatibility

• E-mount - The connection between the lens and the camera body, common to all the Sony camera bodies on this site.
• FE (Full-frame E-mount) - A Sony E-mount lens designed to cover a full-frame sensor. Without the F ("E" alone), the lens is meant for a smaller sensor (APS-C).
• DG DN (Sigma) - DG indicates that the lens is designed for a full-frame sensor, and DN (Digital Neo) that it is designed for mirrorless cameras.
• Di III (Tamron) - Di (Digitally integrated) denotes lenses designed for full-frame digital, and III the design generation for mirrorless cameras.

The ranges

• G - Sony's advanced range: very good optical quality at a more moderate price and weight.
• GM (G Master) - Sony's high-end range, with the best sharpness and the most beautiful blur rendering.
• Art - Sigma's high-end range, comparable to Sony's G Master. Art is a range name, not an acronym.
• PZ (Power Zoom) - Motorised zoom, handy in video because the focal length change is smooth and silent.
• Macro - A lens able to photograph from very close, with a magnification of up to 1:1 (the subject is the same size on the sensor as in reality).
• II - The second generation of the same lens, usually lighter and faster.

Focal length and aperture

• mm (millimetre) - The unit of focal length, that is of the optical distance that determines the angle of view. The shorter it is, the wider the angle (see the article on focal length, sensor and field of view).
• Prime lens - A single focal length (50 mm, 85 mm). It is often brighter and more compact than a zoom.
• Zoom - Variable focal length (16-35 mm, 70-200 mm). The gap between the two values gives the range.
• Wide-angle and telephoto - A wide-angle (under 35 mm) sees wide, for landscape and astrophotography. A telephoto (over 85 mm) brings distant subjects closer, for wildlife and sport.
• f/ (f-number) - The ratio between the focal length and the diameter of the diaphragm. The smaller the number, the brighter the lens (f/1.8, f/2.8).
• Maximum aperture - The smallest f/ number the lens can show. It lets in more light and blurs the background more. For a zoom, an aperture given with two values (f/5.6-6.3) means it decreases as the focal length increases.
• Bokeh - The quality of the background blur (a Japanese word). It depends on the aperture and on the number of diaphragm blades: the more there are (11 on the 70-200 mm f/2.8 GM II), the rounder the blurred points of light.
• Minimum focusing distance - The shortest distance at which the lens can focus (0.4 m at 70 mm for the 70-200 mm f/2.8 GM II). It measures the ability to photograph up close.
• TC (teleconverter) - An element placed between the camera body and the lens that multiplies the focal length (1.4× or 2×), at the cost of some light. The name "FE 300mm f/2.8 GM + TC" refers to the lens used with a teleconverter.

Stabilisation and autofocus

• OSS (Optical SteadyShot) - Optical stabilisation in the lens: a group of lens elements moves to compensate for shake. It complements the camera body's own, especially at long focal lengths.
• AF (autofocus) - Automatic focusing, driven by a motor in the lens.
• MF (Manual Focus) - Manual focusing, with the ring.
• DMF (Direct Manual Focus) - Manual focusing possible at any time, even in autofocus, by simply turning the ring.
• XD linear motor (eXtreme Dynamic) - The autofocus motor of Sony's high-end lenses: fast, precise and silent (useful for video).
• VXD (Voice-coil eXtreme-torque Drive) - Tamron's linear motor for fast, silent autofocus.

Optical construction

• Aspherical element - A lens element whose curvature is not that of a sphere, which improves sharpness across the whole image.
• XA (eXtreme Aspherical) - Sony's most precisely surfaced aspherical element, which avoids "onion ring" blur (concentric circles in blurred points of light).
• ED (Extra-low Dispersion) - Extra-low dispersion glass, which limits colour fringes (chromatic aberration). Super ED glass is an even higher-performing version.
• Nano AR (Anti-Reflective) - An anti-reflective coating on the lens elements, which reduces reflections and ghosting (stray light when facing a light source).
• MTF (Modulation Transfer Function) - A curve that measures a lens's sharpness and contrast from the centre towards the edges of the image.
• Fluorine coating - A layer on the front element that repels water and fingerprints, and is easy to clean.
• Dust and moisture resistance - Seals that protect the lens from the weather, without making it waterproof.

Weight and dimensions

• Weight - Given in grams. It matters a lot when travelling and hiking.
• Diameter and length - The lens's dimensions in millimetres, useful to know whether it fits in your bag.