Photography is all about capturing light on a photographic emulsion or electronic sensor. And as such the lens, film or sensor are the most important components affecting image quality. Essentially, the camera itself is just a light-tight box with a shutter!
[b]Lens[/b]You've seen the fabulous pictures from the rovers sent by Nasa to Mars. All detailed and colourful. You might think that they're from some huge megapixel space-age techno-beast and you'd be surprised to hear that the sensor is a paltry 1 megapixel. Bigger pixels mean less noise which is all the time a good thing, but where Nasa put all its money was into a very high potential lens. The results show it was worth it!
A camera that allows you to turn the lens will obviously give you the most flexibility to pick the appropriate lens for the situation. An ideal camera like this is the Slr. You can select from super wideangle to super telephoto. Macro for close ups. Bellows for even closer close up. Attach it to a microscope. Attach it to a telescope.
Primes Vs Zooms
Prime (fixed) focals have the benefit of being fast (bright) and very high potential by virtue of the fact that they can be designed just for that focal length. A zoom lens allows a option from a continuous range of focal lengths. They are beneficial where you need a range of focal lengths but want the convenience of a single lens, either for weight (only one lens), all the time being ready to take the photograph or shooting in a dusty environment and you want to keep debris entering the camera to a minimum (you also need to think about how to turn films).
This all sounds great but there are drawbacks. Zooms are slower than primes (smaller minimum aperture) and can thus make hand holding and focusing (whether manual or auto) problematic. Also due to their complexity zoom lenses suffer from more abberations than primes. Lenses from the major camera makers tend to be very good. Third party zooms vary considerably. Like all else, you tend to get what you pay for.
Zooming is more than just getting closer. It alters the focal distance and affects the perspective and depth of field of the picture. Think either you should zoom in and use a longer focal length, or get closer and use a shorter focal length?
Focal Lengths
Standard Lenses (~50mm)
A appropriate lens is the usual lens supplied with an Slr. They are good normal purpose lenses having an angle of view close to the human eye. They are sharp, covenant and lightweight.
Small "standard" zooms have a range of typically 35-70mm (2x), 28-85mm (3x) or 24-105mm (4x). These zooms often replace the 50mm lens.
A typical covenant has a zoom lens with a focal range of 35-100mm.
Wideangle Lenses (135mm)
Used for sports, nature or other types of documentary style photography that requires you to be close to the performance but cannot be close physically be it dangerous or timid. Like portrait lenses they are great for picking out the subject from the background.
Other extra Lenses
Macro
Macro lenses can focus very close allowing real size, 1:1 image ratios, ie an object 10mm in size will appear 10mm on the 35mm frame. Excellent for nice close ups of insects or flowers.
Fisheye Lenses
Distort the perspective to generate a circular "fisheye" 180° image. A very specialised lens. Picking the precise subject is principal but when you do can yield some memorable images. Focal lengths vary, 7~16mm.
Super Wideangle Lenses (300mm)
Longer telephotos and an eye-watering price tag to match. Can be heavy due to the whole of glass they contain. Often they have a tripod mount on the lens. You will need to tripod mount to sell out camera shake and weight of lens (unless you're after a work out!) Favoured by tabloid journalist when spying on celebrities!
Other Terms
Fast Lenses
A fast lens is one that has a large minimum aperture and is often a good thing. The minimum aperture might be f/1.4 or f/2.8 or whatever is appropriate for the lens compared to other lenses of the same focal length. Obviously the larger minimum aperture requires larger glass elements and is consequently heavier and maybe bulkier than a lens one or two slops slower. They are often higher potential as a side-effect of the lens maker justifing the extra expense.
Mirror or Reflex Lenses
It is possible to make lenses using mirrors to fold and focus the light rather than glass and are also known as catadioptric lenses. Many telescopes are like this. The advantages of this type of lens are compactness and reduced weight. Long glass telephotos are big and heavy beasts. The reflex equivalent is covenant and lighter making hand holding possible. Like big telephotos, they normally have built-in rear-mounted filters. Catadioptrics also yield characteristic doughnut shaped out-of-focus highlights, or bokeh, which can be quite pleasing.
Apochromatic Lenses
An apochromatic lens is designed to focus three wavelengths of light, corresponding to the colours red, green and blue, onto the film plane. This reduces chromatic abberations, or the phenomenon of dissimilar wavelengths being focused at dissimilar distances or dissimilar point of the film plane. Chromatic abberation appears as coloured fringing nearby high contrasts objects typically a red fringe on one side and a purple fringe on the other. normal lenses are called achromatic and they are designed to focus two wavelengths (red and blue) onto the film place and the designer assumes that all between will be similarly focused. Apocromatic lenses are also designed to focus two wavelengths at the edges to sell out rotund abberations. rotund aberrations show up as unfocused portions of the frame normally at the edges and at larger apertures. To achieve these feats some or all of the optics in an apochromatic lens are made from extra (expensive) glass. Apochromitic lenses can be expensive!
Specialised Lenses
Varisoft Lenses
Allows the photographer to adjust the whole of rotund aberration to generate a distinctive soft focus effect. The lens has a operate ring to set the whole of softness. Excellent for portraits. Creates more reproducible results than the alternative, but much cheaper, version of smearing vaseline on a skylight filter.
Shift Lenses
With a wideangle lens the exaggerated perspective can make tall buildings look like they are curving inward (or outward) if the camera is tilting slightly upward (or downward). Having the camera perfectly vertical (specifically parallel to the buildings) fixes the
distortion but might not be the photograph you are after. The shift lens allow the photographer to precise the distortion so that the buildings are straight again. Great for architectural photography and for panoramic shots intended to be stitched together.
Lens Care
Don't use tissue to clean your favourite camera lens as it only redistributes the oily dirt and leaves tiny scratches. Use a blower brush, cleaning fluid and a lint free cloth.
Hand Held Photos
You might ask is: what is the slowest shutter speed I can use and still hand hold and get appropriate results? If you've ever used a telephoto before, you'll know that the longer the focal distance the more difficult it is to hold the camera steady. That is why binoculars with ridiculous magnifications are impossible to use hand held.
A cheap rule-of-thumb seems to be you can allow the shutter speed to drop to the inverse of the focal length. So a 200mm lens would be 1/200" and a 28mm lens would be 1/30". Naturally, all this depends on your own steadiness.
Of course, nowadays, electronics takes all the fun out of trying to hold the camera steady after a night on the pop. Anti-shake sensors and Ccd scanning tricks can unmistakably cope with moderate shaking and they seem to work well.
Notes For Digital Cameras
Comparison with 35mm
The sensor in a digital camera (Ccd, Cmos etc) can vary in size. As new technology arrives they can get smaller or bigger and so the focal lengths of the lens can be difficult to review to. To solve this the focal distance is often specified as a 35mm equivalent, This is as if the sensor was scaled up to 35mm frame size (36x24mm) and focal distance accordingly.
Digital Zoom
The most useless and over-marketed feature of a digital camera. I mean, what were they thinking? Most places quite wisely tell you to ignore the digital zoom. It is nothing more than cropping and enlarging a measure of the image with a resultant loss of resolution. It does not (and cannot) alter the focal length. Switch it off and use imaging software on your desktop Pc to achieve great results if you need to crop.
Photography - The Lens
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