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The invention of the telescope changed forever the way we look at the world and, indeed, the universe. Once we discovered that glass and mirrored surfaces could be ground and moulded to manipulate the perspective of light the art of optics was free to evolve. Today's highly sophisticated lenses are are the pinnacle of this science. Concave and convex lens elements can be mounted in a barrel to produce a huge range of lenses from the bulging fish-eye lens to monstrous telephoto lenses which capture remarkable detail of wild animals from a great distance.
Glass lenses are recognised for their superior clarity, but being crafted by hand they come with a prohibitive price tag. Furthermore, they are heavy and, being glass, can shatter if dropped. Most camera lenses these days are manufactured using high quality transparent resins, ground to exact specifications using computer technology. They are lightweight and rugged, ideal for most photographic situations. The optics of any reputable camera, whether SLR, bridge or compact, are quite impressive. With advanced methods of assembling zoom lenses and a new generation of lens coatings, even the smallest cameras will produce amazingly sharp images over an impressive range, from wide angle to highly magnified telephoto.
There are a couple of basic things to remember with modern lenses.
A quality, dedicated fixed lens will always produce a sharper image than its zoom equivalent. A fixed focal length 300mm telephoto lens will out perform a zoom lens extended to 300mm for the simple reason that there are fewer lens elements used in its construction. This translates into less distortion and reduced internal reflection. However, a quality zoom lens is capable of producing such good results that the difference is hardly noticeable in most situations. Most photographers will settle for the versatility and convenience of a zoom. The minor sacrifice of quality is negligible.
A dedicated lens is also faster than its zoom equivalent. The "speed" of a lens refers to the amount of light that passes through the lens. The lens is a collection optical elements (also called lenses) mounted in a row. Each of these is chemically coated to reduce reflection and distortion. By the time a beam of light passes through this cluster it will have lost some of its brightness. This will affect the exposure, slowing the lens down. Big lenses, like the giants that sports photographers use, have large, bright lens elements that allow plenty of light through to the camera sensor. These fast lens increase performance in low light conditions. However, the large lens elements increase the likelihood of distortion and reflection within the barrel. I use a basic 75-300mm zoom lens which I bought for $180 on eBay. Alongside its $4000 BIG brother (L-series Canon 75-300 lens) it looks quite impotent. In a blind test of the two side-by-side, I could not pick the difference in clarity. However, the high speed of the L-series lens gives it an enormous advantage in action photography in low light. It weighs a ton and requires a tripod to support it. For my purposes the small size and light weight of my versatile telephoto lens works brilliantly.
OBSERVATIONS AND TIPS
| If you like the occasional image with the main subject in sharp focus and everything else a soft, dreamy blur, then zoom into the telephoto range. The more you zoom in, the more the effect will be accentuated. If you use a manual setting remember that a wide aperture means only a small area of the image will be in focus |
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Here is a great idea. A friend of mine has days when he shoots only with a telephoto lens. It is a great exercise in understanding the versatility of this lens. Give it a go.
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| An attractive feature of the telephoto lens is that it not only magnifies the subject, it compresses it. This is a great effect where distant objects and closer objects all appear to be much the same size. If you want everything to be in focus, manually set a small aperture. |
| The telephoto lens not only magnifies the subject, it magnifies any movement in the camera. The more you zoom in, the more camera shake will be apparent. A lens with a stabiliser will overcome some of this, but there no substitute for a tripod. A word of advice though. If you use a tripod make sure that you turn the stabiliser on your lens off. The gyros in the stabiliser may generate vibrations in their attempt to stabilise an already stable lens. |
| The telephoto lens can also be used for close subjects. Used between 135 and 180mm, it is a brilliant portrait lens. At a range of about 2 metres it can be used as a close-up lens - not exactly a macro, but provides a very different perspective on the subject. |
| Most compact and bridge cameras offer the option of using the optical or digital zoom. It is good policy to switch the digital zoom permanently off. It is only an optical illusion which results in fuzzy, poor quality images. |
| If you are using an SLR camera you might be tempted to purchase a 2X converter to double the focal length of your lens. Unless you pay top dollar for such a device, don't expect miracles. There will inevitably be a drop-off in quality. Only tailor made converters designed for specific lenses will yield good results. |
| What constitutes telephoto? Anything greater than a 1:1 ratio. In SLR parley 50mm is 1:1. Any focal length greater than 50mm is telephoto.When it comes to field use you will usually discover that the higher the focal length of a lens, the more limited its use will be. For example, a 600mm lens is a highly specialised tool, ideal for wildlife photography but rarely used for average photography. There is quite an art to using a very large lens. |
| The telephoto lens is a good option for adverse lighting conditions - overcast, wet days. I describe these as "doors and windows" days. A steely gray sky can play havoc with exposure. By selectively zooming in, the impact of the sky can be kept to a minimum. |
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