Lens mount

This is the physical connection between a lens and the body of a DSLR or mirrorless camera. It consists of a twist-lock bayonet mount and electrical connectors. The lens mount is specific to a camera brand – you have to make sure you get lenses in the right fitting for your camera.

Lens hood

Lens hoods can reduce lens flare and improve contrast when there’s a bright light source just outside the edge of the frame, but they won’t help if the sun, for example, is in the frame. Lens hoods are usually ‘petal’ types that allow for the fact the image frame is rectangular.

Kit lens

A relatively inexpensive general purpose lens sold with a camera body as a kit. Buying both at the same time is much cheaper than buying them individually. Most DSLRs and mirrorless cameras are also sold ‘body only’ for those who already have lenses.

Focal length

This tells you a lens’s magnification or angle of view (it’s the same thing really) and it’s quoted in millimetres. Sometimes the makers quote actual millimetres and sometimes they quote the ‘effective’ focal length, which is what the lens would be equivalent to if it was a 35mm camera.

Fisheye lens

A fisheye is an ultra-wideangle lens that no longer attempts to render straight lines as straight and instead produces images with strongly curved edges and a characteristically surreal look. It’s a striking effect, though one to be used occasionally.

Effective focal length

The angle of view of a lens changes according to the size of the sensor in the camera. A smaller sensor captures a narrower angle of view and makes it look as if the lens has a longer focal length. So in addition to the actual focal length, the manufacturers will usually quote the ‘effective’ focal length too.

Digital zoom

Zoom function that comes from blowing up the central part of a digital image, not by increasing the magnification of the lens. Digital zooms produce lower resolution and less detail, despite what the makers say.


Mechanism inside a lens which uses interlocking metal leaves, or ‘blades’, to produce a variable-sized aperture within the lens. This is used to control the amount of light passing through and hence the exposure.

Depth of field preview

Usually you view the scene with the camera lens wide open and it only stops down to your chosen aperture the moment you press the shutter button, so it’s hard to judge just how much depth of field the final photo will have. The depth of field preview stops the lens down to the taking aperture, though, so you can judge the effect in the viewfinder or on the LCD display.

Depth of field

Depth of field is the near-to-far sharpness in a picture. If both foreground and distant objects are sharp, there’s lot’s of depth of field – this shot is a good example. If only the subject is sharp and the foreground and background are blurred, it’s shallow d

Crop factor

Used to work out the effective focal length of lenses on cameras which don’t have full frame sensors. You multiply the actual focal length by the crop factor to get the effective focal length. The crop factor of an APS-C camera is 1.5, so a 50mm lens has an effective focal length of 75mm.