Do you know your OS from your HSM? If you’re a photography novice or have been out of the game for a while, then probably not; all the different labels and acronyms on lenses can be confusing. Each lens manufacturer is keen to let you know their technology is superior to competitors. Most of their features have a unique name but perform the same task!
If you'd like a quick refresh on focal lengths, prime & zoom lenses and apertures then try our fantastic Lens Sense Guide.
Image stabilisation
Image stabilisation is used to reduce camera shake which can blur images, often experienced at slow shutter speeds or whilst using long telephoto lenses. Image stabilisation is applied either within the lens (known as optical image stabilisation) or to the sensor (favoured by Olympus, Sony and Pentax).
Image stabilisation terms for each manufacturer:
- Canon: Image Stabilisation (IS)
- Nikon: Vibration Reduction (VR)
- Sigma: Optical Stabiliser (OS)
- Tamron: Vibration Compensation (VC)
Image Stabilisation Tips:
- Image stabilisation is only effective with static subjects (moving objects will still blur if the shutter speed is too low).
- Switch off image stabilisation when you are using a tripod (leaving it on could make your images softer!).
- If your shutter speed is fast enough to compensate for camera shake (e.g. bright conditions), switch image stabilisation off to extend your battery life.
In-Lens Autofocus Motor
To autofocus (AF) the camera must adjust glass elements inside the lens till the subject is sharp (determined by an AF sensor). The AF motor to adjust the focus is located in either the camera body or the lens itself. Lenses with integrated autofocus motors tend to be quieter and faster than lenses that require the camera body to AF (using a screw driven mechanism).
In-lens autofocus motor terms for each manufacturer:
- Canon: Ultrasonic Motor (USM).
Available in two flavours: ring-type USM and micro USM. - Nikon: Silent Wave Motor (SWM).
Also designated by ‘AF-S’ in the lens name. - Sigma: Hyper-Sonic Motor (HSM).
- Pentax: Supersonic Drive Motor (SDM).
- Tamron: Built-in Motor (BIM). For select Nikon fit Tamron lenses (look for ‘with AF motor’).
- Olympus: Supersonic Wave Drive (SWD).
- Sony: SuperSonic Motor (SSM) or Smooth Autofocus Motor (SAM).
Autofocus Tips:
- If you plan to take photographs of fast moving subjects (sports action or wildlife) then a lens with an ultrasonic AF motor should increase your percentage of images in-focus (‘keeper rate’).
- Newer entry-level digital SLRs from Nikon (D40, D60, and D5000) will only autofocus using lenses with integrated AF motors.
Digital (Only) Lenses
Often a slight misnomer, ‘digital lenses’ can imply the lens is optimised for a digital camera, but still work on a full-frame digital SLR (big sensor) or film camera. In contrast digital only lenses are designed for digital SLR cameras with APS-C sized sensors (smaller ‘cropped’ sensors). Digital only lenses won’t work on full-frame digital SLRs (despite being a digital SLR). If that’s a headache, don’t worry too much unless you are using a film camera or expensive digital SLR (over £1500) – the vast majority of current lenses will work with your camera.
Digital only lens terms for each manufacturer:
- Canon: EF-S.
A variation of the EF lens mount where the ‘S’ represents “short back focus”. EF-S lenses can only be used on Canon EOS digital SLRs with an APS-C size sensor. Normal Canon EF lenses can be used with all Canon EOS cameras, film and digital. - Nikon: DX.
Refers to compatibility with Nikon digital SLRs using a DX size sensor (very similar to APS-C). The image circle will not cover the entire sensor on Nikon full-frame FX digital SLRs. - Sigma: DC.
- Tamron: Di-II. Stands for “Digitally Integrated Design” II. Lenses with just ‘Di’ (without mark II) are compatible with film and full-frame digital SLRs.
- Sony: DT.
- Olympus: ZUIKO. The entire Olympus ZUIKO lens line-up is designed for E-system digital SLRs with smaller sensors.
Digital Lens Tip:
- Digital only lenses, optimised for smaller APS-C sized sensor, are smaller and lighter than their counterparts for film and full-frame digital SLR cameras.
Low Dispersion Glass
As light passes through optical glass the different wavelengths of light can be spread apart. This causes coloured fringes or smudges to appear in your images around the edges of objects. This effect is known as chromatic aberration (CA), also referred to as “purple fringing” (the violet wavelength is more susceptible to chromatic aberration). To combat this manufacturers use exotic glass or elements. If peak-performance image quality is vital to you then keep an eye out for these terms:
- Canon: Fluorite and Ultra Low Dispersion (UD) glass.
- Nikon, Pentax & Olympus: Extra-low Dispersion (ED) glass.
- Sigma: APO lenses which feature Special Low-Dispersion (SLD) glass.
- Tokina: Super Low Dispersion (SD) glass.
- Tamron: Low Dispersion (LD) and Anomalous Dispersion (AD) glass.
If you are planning to buy a lens hopefully this article demystifies some of most common lens terms around today.