This site contains affiliate links for which I may be compensated.
How focal length affects the image
These pictures show how the different focal lengths will affect your image, on different sized sensors. There’s more about using lenses on this page.Wide angle
Focal length: Full-frame around 24-40mm; APS-C 15-24mm; MFT 10-17mm; iPhone 1x
These lenses are very useful for filming master shots of a whole scene, or getting in close and working in cramped spaces. They’re easy to handhold, perspective looks dramatic, and there’s good depth of field (a lot of the shot is in focus at the same time). The big drawback is that closeups will be distorted. If you want to shoot with just one prime lens, this may be the one to have.
Standard
Focal length: Full-frame around 50mm; APS-C around 35mm; MFT 20-25mm; iPhone 2x
These lenses offer natural-looking perspective. They’re good for two-shots of people, and mid shots (hips to head) but they give slight distortion if you use them for closeups. 50mm prime lenses are usually small and ‘fast’ (they have a wide maximum aperture to let in a lot of light). f/1.8 versions are compact and give excellent image quality for the money; faster versions (1.4 or 1.2) are bigger and more expensive. The wide maximum apertures make for shallow depth of field: good if you want to use focus creatively, not so good if you need everything to be sharp.
Medium telephoto or ‘portrait’ lens
Focal length: Full-frame around 85-100mm; APS-C around 50-60mm; MFT 35-50mm; iPhone 3x
These are the shortest lenses that will give undistorted closeups. They are usually quite ‘fast’ (they have a wide maximum aperture) which makes them good in low light. But they’re tricky to handhold, so they’re best on a tripod. These lenses seem to flatten perspective (which is good for strong, graphic compositions) and they let you get nice shallow depth of field effects. You’ll need to be accurate with your focusing. If your camera has an APS-C or Super 35 sensor, a 50mm f/1.8 lens – which would be a standard lens on a ‘full frame’ body – makes an excellent, affordable medium telephoto.
Telephoto lens
Focal length: Full-frame, 135mm and above. APS-C 85mm and above. MFT, 60mm and above; iPhone over 4x
Longer telephoto lenses are good for flattening perspective, isolating the subject from the background and bringing distant objects closer. But they are usually big, heavy, slow and need to be used on a tripod or monopod.
Ultrawide
Focal length: Full-frame less than 24mm; APS-C less than 16mm; MFT less than 10mm; iPhone 0.5x
These lenses will fit a lot into the scene. They’re easy to handhold and have very good depth of field. But closeups and the edges of shots will be very distorted, and it’ll be very obvious if the lens isn’t level. These lenses are good for fast, fly-on-the-wall documentary work because they let you get really close to the subject, and the dramatic perspective can make pretty much anything look interesting. Good quality ultrawide lenses for system cameras are expensive.
Lens features to look for
Optical image stabilisation
This can be important if you need to shoot handheld without a tripod.
Electronic or mechanical focusing
Many modern camera lenses are ‘fly-by-wire’: you turn a physical focus ring, but an electronic motor adjusts the focus. How much the focus changes will depend on how fast you turn the focus ring.
This is OK if you mainly use autofocus. But it doesn’t work well if you want to pull (change) focus manually. So you might prefer lenses with mechanical focus rings made by third party manufacturers, or vintage prime lenses which were built before autofocus became common.
Parfocal lenses
A parfocal lens holds its focus when you zoom in and out. This can be important when you’re working quickly.
Focus breathing
With some lenses, image size can change very slightly as you adjust the focus. This can be distracting if you pull focus. More expensive, higher quality modern lenses are designed to minimise this.
Focal length and sensor size
‘Full-frame’ sensors, used on high-end Canon, Sony and Panasonic cameras, are about the same size as 35mm still camera film. Sensors that are smaller than this are sometimes called crop sensors. ‘Crop factor’ means how much smaller the sensor is than a ‘full-frame’ 35mm still camera frame. This lets you compare lenses on different sensors. So an 18mm lens on a camera with a crop factor of 1.6 will have the same field of view as a 29mm lens on a full frame 35mm still camera. (18 x 1.6 = 29)
- APS-C sensors are used on many mid-range cameras made by Canon, Nikon and Sony. They are about the same size as a 35mm movie camera frame. Canon APS-C cameras have a crop factor of around 1.6; with Nikon, Sony and Fujifilm it’s 1.5.
- Some cameras, such as the Canon Cinema EOS range, have slightly larger Super 35 sensors with a 1.4-1.5 crop factor. They can usually use lenses designed for APS-C.
- MFT (Micro Four Thirds) is a smaller sensor size used on Olympus and Panasonic cameras, and the BlackMagic Pocket Cinema Camera 4K. The crop factor varies from 2-2.6 depending on which camera you have and whether you’re filming HD or 4K (more on this page).
You can use lenses designed for full frame on cameras with smaller sensors, though you may need an adaptor. (For compact cameras, it’s best to find out what the ‘35mm equivalent’ is.) Many Panasonic MFT users buy optical Metabones Speedbooster adapters, which let them use – and get the effect of – full-frame lenses with the smaller Panasonic sensor.