Lenses

Lenses

What are the types of camera lenses?

• Camera lenses are defined by two key factors.  The first is the focal length.  You can check the focal length of a simple lens by pointing it towards the sun with one hand and using your other hand to find the point at which the sun's rays come together to cause the maximum pain. It was a favourite of science teachers in the more boring days after the Blitz.  
• The second is the width or diameter.  A stronger lens, ie one with more bend to it, has a shorter focal length.  It will bring the sun's rays together more closely and hurt more.  Short, or 'wide angle' lenses produce a brighter image than lenses with a longer focal length which spread out, or magnify, the image across a wider area.
• To save a lot of re-calculation when you change lenses, their diameter is expressed as a fraction of the focal length - eg focal length/2 or f/2.  This figure is the relative aperture and defines the brightness of the image formed by any lens.  An f/1 lens is as wide as it is long. A 100mm lens with a maximum aperture of f/2 will be 100/2 i.e. 50mm wide.  It will have a thread at the front to accept a UV or protector filter which will need to be slightly larger than that - maybe 62 or 67mm
• Camera lenses are generally classified according to their angle of view and whether this is fixed or variable. A standard lens is one that has much the same angle of view as our own eyes which is around 55 degrees. Anything with a wider view is called a wide-angle lens.  It includes more of the subject area in the picture and so everything is smaller than in a photo taken with a standard lens.  A more restricted angle takes you through portrait lenses, useful to fill the picture with the just the head and shoulders of your subject to telephoto lenses which act in much the same way as a telescope.
• Lenses which can change their angle of view were originally called Vari-angle lenses but have now become Zoom lenses.  They can be Wide-Angle zooms, Mid-Range Zooms, Telephoto-Zooms or even Ultra-Zooms.
• Interchangeable lenses became popular in the 70s when the 35mm films and cameras of the time became good enough to challenge the supremacy of larger formats. They were popularised by the likes of David Bailey and slogans like 'Just hold a Pentax'.  The image captured and recorded on 35mm film was 24x36mm, a format that has continued into the digital era on top-end cameras with a 'full-frame' sensor. 
• A standard lens is one that equates to the diagonal of the image, in the case of 35mm film, or full-frame digital, 43mm.  Originally, they mostly came with a slightly longer 50mm standard lens and latterly a mid-range zoom, maybe from 28-70 or 24-100.  The focal lengths that were popular then have stuck in photographer's minds ever since and are often quoted on compact cameras as "35mm equivalent". For enthusiasts with a full-frame digital camera, the old lenses perform exactly as they did in film days which was 'not as well as the latest versions'.
• Cameras with smaller sensors will crop off the edges of the frame and so produce the same effect as cropping, or blowing up the centre of the image, in post-production. They are therefore a good tool for extreme wildlife or sports photography, creating the final image in-camera faster and using less memory.
• Early digital cameras used a reflex mirror and screen to view the image in the same way as a 35mm SLR. In recent years, all the major manufacturers have gone 'mirrorless' with ranges of cameras that rely totally on digital imaging to both view, review and record the image. Doing away with the mirror allows mirrorless cameras to be slimmer.  Therefore, 'mirrorless' lenses are slightly longer and SLR lenses can be used with an optional adaptor.  The Sigma MC-11 that adapts Canon EOS SLR lenses to any Sony Alpha proved extremely popular prior to Canon's launch of its own mirrorless R system and their own series of EF to RF adaptors.