Lenses for Digital Cameras: The Basics
For those who have opted to move on from point-and-shoot digital pocket cameras to digital cameras with interchangeable lenses, how do you decide what lenses to buy? Should you always use the same manufacturer’s lenses that come with the camera? Are zoom lenses inherently inferior to fixed length lenses? What would you use a close-up (macro) lens, and why do you need a fish-eye lens? Here’s some basic assistance.
The focal length of a camera lens is measured in mm with the ‘standard’ lens for a 35mm camera being 50mm and having an angle of view of 45 degrees. Shorter lenses are referred to as ‘wide angle’ and have a wider angle of view, often 80 or 90 degrees. Lenses longer than 50mm are ‘telephoto’ with progressively narrower angles of view as the focal length increases. Zoom lenses can be of the telephoto or wide angle variety (or both) and have the added feature of being able to alter their focal length within a given range. Macro lenses allow close-up photos by extending lens from camera body further than usual.
Of course, the lens you should first buy depends on what you’re planning to do with a camera. I had a friend who bought five lenses in the first year of his getting a Digital SLR camera, and when I saw him a year later, he had only used two of them!
For the beginner, a wide angle lens is used because it ‘fits it all in’ while telephoto lenses are used to ‘get closer’. What are the other factors that affect a lens?
“Perspective” is enhanced with the use of wide angle lenses and compressed when shooting with telephoto lenses. This is often as much a reason for choosing a lens as its angle of view. A super-wide lens will dramatically increase the size of the subject in the foreground in relation to the background, making it the first choice of many landscape and press photographers. On the other hand, a telephoto lens will ‘pull together’ the foreground and background which is useful when repetition needs to be shown (eg. Pylons or telegraph poles in a row).
“Depth of field” is the area of sharp focus behind and in front of the subject you are primarily focused on. Depending on your subject, either telephoto or wide-angle lenses can fulfil your needs – the telephoto separating the subject from the background and the wide angle, layering the subject upon the background.
Turning to zoom lenses. These were invented over three decades ago, and yet controversy still rumbles about them! There is no doubt that zoom lenses are convenient and versatile and if chosen carefully, will produce many great images, but you should consider the following: Zoom lenses tend to be ‘slower’ than their non-zoom counterparts. This is a reference to the maximum aperture of the lens (eg. f5.6) which will affect ease of focussing, shooting in low-light etc…
Zoom lenses which offer a wide angle to telephoto range (eg. 28 – 200mm) often exhibit a multitude of optical problems such as pincushion or barrel distortion, as well as loss of sharpness and illumination in the corners of the frame.
Ultimately with all lenses, you get what you pay for, so don’t expect miracles from a generic brand zoom which is offered to you when buying your new camera body. It’ll probably be OK for small prints, but you’ll certainly see the difference when you start to enlarge or shoot transparency film.
Finally, looking at wide angle lenses; with recent innovations in design, excellent lenses are available starting at a focal length of 14mm. In layman’s terms – if you used this lens standing in the corner of a room, you would see both walls on each side of the camera (as well as the entirety of the room). I would avoid buying an extreme wide angle lens- a fish –eye lens, because it is so obviously a distortion that it is only useful for special effect photography, and unlikely to be used very much.
I hope this guide is a good starter towards what lens to get as your first addition. Oh, and don’t forget lens filters- but that’s another story! Want to know more about cameras, read this site.
Stephen Cruze
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