Sigma Cine 20mm T1.5 FF

Technical glossary

AFL button
Found on the barrel of some Sigma lenses, this button can be assigned to various functions to widen the range of operations available on the lens (available functions depend on the camera model).

Aperture ring
Allows users to change aperture using the lens rather than the camera. The ‘Auto’ button on the ring switches aperture control to the camera.

Aperture Ring Click switch
Some lenses with an aperture ring have a click switch, which allows users to remove the ring’s clicking action. This means the aperture can be changed completely seamlessly rather than in stepped 1/3-stop increments. The function is ideal for film-makers.

Aperture Ring Lock switch
This switch locks the aperture ring in either manual or auto, ensuring it can’t get knocked out of position when shooting.

Art
One of the three lines of Global Vision lenses. The Art range includes a mixture of primes and zooms, which boast fast apertures, superb optics and exceptional build quality.

Aspherical lens
A type of lens element found in most Sigma lenses. Aspherical elements compensate for spherical aberration and distortion, which cannot be completely eliminated using conventional spherical lens elements alone. They are also key to reducing the size and weight of high-power zooms and other large lenses while improving image quality. Hybrid aspherical elements are made by bonding two elements together, one of which is glass and one of which is a polymer. Precision-molded glass aspherical elements are made by direct forming.

Brass bayonet mount
All Sigma lenses have a brass mount. It combines high precision with rugged construction and its treated surfaces and enhanced strength contribute to the long-term durability of the lens.

CFRP (Carbon Fibre Reinforced Plastic)
A light but strong material used on some Sigma lenses. It is also used in the interior and exterior fittings of aircraft, among many other applications.

Contemporary
Designed with size and weight in mind, these highly portable primes and zooms are designed for photographers who need to travel light, but without sacrificing image quality. Contemporary lenses typically don’t have such wide maximum apertures as Art lenses in order to keep their weight down, but do not compromise on optical performance. The I series range is part of the Contemporary line-up, sporting have an all-metal build and a manual aperture ring.

DC
Designed for crop-sensor cameras. They can also be used on full-frame bodies, but only in crop mode.

DN
Designed specifically for mirrorless cameras. Some non-DN lenses also fit mirrorless cameras, but these were designed originally for DSLRs and later adapted. DN lenses tend to be smaller and lighter.

Dual Action Zoom
This is found on some longer Sigma lenses, such as the 60-600mm F4.5-6.3 DG DN OS | Sports. It allows the user to zoom either by turning the zoom ring, which is very accurate, or by pushing and pulling the end of the lens, which is very fast. This makes the lens very adaptable to different types of fast-action subject.

Dust - and splash - resistant structure
A series of weather seals around the mount connection, manual focus ring, zoom ring and cover connection to keep out dust and water. Although this construction allows the lens to be used in light rain, it is not the same as being waterproof, so please prevent large amounts of water from splashing on the lens.

Edition number
The three-digit code printed on the surface of the lens is to indicate the year the lens was first released. 019, for example, denotes 2019.

EX
A now near-defunct designation used to denote Sigma’s higher-end lenses. The only remaining current EX lens is the 105mm F2.8 EX DG OS HSM MACRO.

Extra Low Dispersion glass (ELD)
The degree to which light is refracted by glass depends on the light’s wavelength. This fact causes different colours of light to focus at slightly different points. The result is chromatic aberration, the colour fringing that is particularly noticeable in telephoto lenses. ELD glass is a type of glass used in Sigma lenses with low dispersion qualities, which helps to keep chromatic aberration to a minimum.

FLD (‘F’ Low Dispersion) glass
The degree to which light is refracted by glass depends on the light’s wavelength. This fact causes different colours of light to focus at slightly different points. The result is chromatic aberration, the colour fringing that is particularly noticeable in telephoto lenses. FLD glass is ultra-low-dispersion glass that offers performance of the highest level. Highly transparent, its refractive index and dispersion are extremely low as compared to conventional types of glass. It offers characteristics very similar to those of fluorite, which is valued for its anomalous dispersion. These characteristics minimize residual chromatic aberration (secondary spectrum), which cannot be corrected by ordinary optical glass, while helping to produce sharp, high-contrast images.

Floating system
This system adjusts the distance between lens groups during focusing, thereby reducing the amount of lens movement required. The result is less aberration at different shooting distances.

Focus Limiter
This switch, found on selected Sigma telephoto lenses, allows users to limit the focusing range to either near distance or far distance. This helps speed up AF, and also ensures the camera won’t attempt to focus on an unwanted area of the frame. For example, when photographing zoo animals through a wire fence a photographer could set the focus limiter to, say, 10m–infinity, to stop the camera continually trying to focus on the fence, which is nearer to the camera than the subject. On some Sigma L-Mount lenses, the distances on the limiter can be customised via the USB Dock.

Focus Mode Switch
Allows user to toggle between focusing modes. On most Sigma lenses the options are AF and MF, but some lenses also have a Manual Override (MO) button, which allows manual focus by rotating the focus ring even during continuous AF.

HLA (High-response Linear Actuator) motor
HLA is SIGMA’s proprietary linear motor. It drives the focus lens directly without going through gears or other mechanical parts, resulting in quiet, high-precision and fast autofocus.

Hood with lock
Some Sigma lenses have a lockable lens hood to ensure they aren’t accidentally removed during use. Some work with a simple release button, while others have a screw action.

HSM (Hyper Sonic Motor)
The Hyper Sonic Motor (HSM) is an original Sigma development that uses ultrasonic waves to drive the autofocus mechanism. It’s extremely quiet and helps avoid disturbing photographic subjects. Sigma uses two types of HSM: ring HSM and micro HSM.

High-precision magnetic sensor
This sensor can detect the position of the focus lens with a high degree of precision using a magnetic signal. This is done in real time to improve AF accuracy.

Inner focus system
This lens configuration uses movable internal lens elements that adjust focus without changing the length of the lens barrel.

Inner Zoom
Some Sigma lenses incorporate an Inner Zoom mechanism, meaning the barrel doesn’t change length when zooming. This ensures balance and makes using polarising filters easier.

Intelligent OS
A stabilisation algorithm that enables photographers to pan more effectively. It uses data from an acceleration sensor to deliver effective stabilization, particularly in panning shots.

Lens Aberration Correction
In-camera correction function for issues such as peripheral illumination, chromatic aberrations, and distortion. Not available on all camera models.

Lens Heater Retainer
A protruding lip at the front of the lens to help keep a lens heater in place. Used in astrophotography to prevent condensation.

Linear focus / Non-linear focus
Linear focusing moves the focus in proportion to ring rotation. Non-linear varies depending on speed. Some Sigma DN lenses allow switching via USB Dock.

Magnification ratio
Describes how large a subject can appear on the sensor. A 1:1 ratio means life-size reproduction.

MFL (Manual Focus Lock) switch
Disengages the focus ring after focusing, so the focus can’t be accidentally altered.

MO (Manual Override)
Allows manual focus by rotating the focus ring, even during continuous AF. Only available on some lenses.

MTF chart
Graph representing lens performance in terms of contrast and resolution. Shows light transmission vs. distance from image center.

Nano Porous Coating
An advanced anti-reflective coating using porous silica with nano-sized holes to reduce flare and ghosting.

OS (Optical Stabilizer) function
Stabilization system that moves lens elements to compensate for hand shake.

Rear filter holder
Allows sheet-type filters to be inserted behind the rear element on select wide-angle lenses.

Rounded diaphragm
Produces circular out-of-focus highlights by using diaphragm blades that keep the aperture circular.

Special Low Dispersion glass (SLD)
Reduces chromatic aberration in telephoto lenses.

Sports
Sigma’s line for fast-action photography, offering advanced features, fast AF and rugged build quality.

Stepping Motor
Offers smooth, quiet and high-speed AF, ideal for video and Face/Eye Detection AF.

Super Multi-Layer Coating
Reduces internal reflections and flare, improving contrast and image clarity.

T stop
Used in cine lenses, measures actual light transmission, unlike F stop which measures aperture size.

Teleconverter
Device that increases focal length of a lens, with 1.4x and 2x being common. Reduces light and affects image quality slightly.

Tripod socket
Attachment point for tripods, especially useful on long lenses. Helps balance the camera-lens system.

TSC (Thermally Stable Composite)
Material with similar thermal expansion to aluminium, keeping lens parts behaving consistently in different temperatures.

Water - and oil - repellent coating
Special lens coating that prevents moisture and oils from sticking to the lens surface.

Zoom Lock switch
Locks the zoom ring in place to prevent lens creep during transportation or use.

Zoom Torque switch
Adjusts the resistance of the zoom ring. Can be set to Soft (S), Tight (T), or Locked (L).