mardi 19 juillet 2005

Zooming Around... Choosing a range of lenses Thirty years or so ago, when I'd become serious enough about photography to give up my full-time designing job, I was faced with the problem of which lenses were the best ones to have in my camera bag. I knew I wanted to take dramatic images with wide-angle lenses... buildings with "perspective control" lenses... close-ups with macro lenses... candids and portraits with medium telephotos... and sports action with long telephotos. However, trying to cover all of the bases all of the time meant a heavy camera bag, tired legs and a sagging shoulder... as I found out later. Nowadays most people buying a camera will not think of any other option than buying it with a zoom lens. If the customer doesn't ask for one the store assistant will suggest it... and often there are "kit" specials where for a small (apparent) increase in price, two zooms will be included... woohooo! And when the assistant confidently states you'll be able to do anything and everything with those bargain-price 18-35mm and 28-200mm zoom lenses, who and how are you - with such an impressive lump of a lens in your hand, with another catching your attention on the counter - able to express any doubt. You are led to believe that your all-encompassing zoom lenses are going to make you the hot-shot on the block! There's actually a contradiction in what I'm leading up to here because for most people the 6x4 inch glossy colour print or the e-mailed J-peg file is the end product... and there's nothing limiting about the quality of the "kit" zoom lenses seen in prints and images of that size. The problems start when you get serious about photography and make prints larger than 10x8 inches... then you will notice the real quality of your images and perhaps start to question the optical quality of your zoom lenses. In the beginning... From the early 1960s the pro system was Nikon - their cameras and optics were literally bullet-proof, as more than one Vietnam war photographer found out living to to tell the tale. One would assume that the really handy (on paper) zoom a decade later, the Nikkor 43-86mm, would have been universally popular... but it was a dog in many photographer's opinions... and so wasn't... though it sold well. Even the expertise of the Nikon factory, keeping to a conservative "two-times" zoom ratio, couldn't produce a sharp design to match their fixed focal length lenses. Mind you, the Nikkor 43-86 wasn't all that bad compared to many of the competition's offerings with odd lengths such as 80-250, 90-230 and 200-550 from Elicar, Hanimex, Komura, Optomax, Sun and Zenith to name a few. But what most lens designers and manufacturers did do in those days was to limit the zoom ratio to, at most, 3-to-1... and for telephoto rather than wide-angle zooms which were more difficult to design. So for a long time the best quality zooms were in the 70-210 category... Nikon holding back a tad with their 80-200 Nikkor zoom utilising a 2.5-to-1 ratio. By the mid-70s major players such as Canon, Minolta, Nikon, Olympus and Pentax were producing wide-angle zooms of good enough quality for all but the most exacting applications... and in the last ten years it can be said that professional zooms have to all intents an purposes caught up with fixed focal length lenses. However, those pro zooms are all around 3x in range... 24-70, 28-85, 35-105 and 70-210... with wide-angle zooms sensibly restricting themselves to a 2x range, the 17-35 being typical. Zooms in the 5x to 10x range are generally not of pro quality. Study catalogues and websites... If you have any misgivings about the optical performance of zoom lenses... look carefully at the latest Nikon and Canon system listings. Each company has over 60 lenses listed, of which probably more than a third are zooms. If these companies have faith in this type of lens, so should you. But before you assume that a zoom is the panacea of all photographic problems, keep in mind that it offers only two advantages over a fixed focal length lens. First, it lets you alter the size of the image on the film without changing lenses or moving the camera. And second, zooming from one focal length to another during a long exposure allows you to create visually exciting effects. If these two features will help you to develop your shooting style, a zoom lens will be a good investment. If not, a wide-aperture, light- weight fixed focal length lens might be better. Although I have several fixed lenses between 20mm and 500mm, I also use two zooms - a wide-tele 28-70mm and longer 80-200mm. These are ideal for general photography and they give the freedom to travel light and shoot fast. Most current zoom lenses are all "two-touch"... this means that the focusing and zooming movements are operated by separate rings. "Single-touch" zooms combine focusing and zooming actions on a single ring making it very easy to alter the focus accidentally as you change the focal length. A zoom lens can be classed as "wide-angle," "mid-range" or "telephoto," depending on the focal lengths covered. Some very specialist designs are starting to break the conventional focal-length barriers - but at the expense of size, weight and cost. For everyday shooting, the limited range zooms offer more advantages than disadvantages. Pro quality counts but costs... The big question mark has to be over quality. There is no doubt that the latest professional zoom lenses from Nikon, Canon or Minolta are excellent in every respect. Computer aided design ensures optimum performance, and special features are used to overcome particular problems. Extra-low dispersion (ED) glass and aspheric elements as well as internal focusing (IF) increase the performance of extreme wide-angle and telephoto zooms which are more prone to aberrations than the mid-range and fixed length lenses. So can a zoom lens capture a similar image to that caught with a fixed focal length lens? It all depends on the lens. A zoom lens will generally have a smaller maximum aperture, making photography more difficult in low light. A bulky zoom lens may be more difficult to hold steady at slow shutter speeds. And although many zooms feature "macro" focusing, they generally fall short of a true macro lens. Although these disadvantages can make zoom lenses appear unattractive, experience proves otherwise. If you are in a wide-angle mood, take a 17-35mm zoom, leaving whichever 17mm, 20mm, 24mm, 28mm and 35mm lenses you have at home. Sometimes I photograph things "normally," and take just the 28-70 zoom. This gives great scope, offering focal lengths from wide-angle to short telephoto in one lens instead of two or three. The same ease of shooting is offered by the 80-200 which lets me leave the 85mm, 135mm and 200mm lenses at home... and fills-in that large gap between the 135 and 200 fixed lenses. This means that you can shoot at say 165mm, if that is the focal length which crops the image exactly as you want it. Composing an image accurately in the viewfinder before the exposure is much more satisfactory that cropping a slide or print after the film has been processed. Weight-watching... In addition to composing convenience there's a worthwhile weight saving advantage. A 28-70mm lens may weigh around 550 gms - the total weight of three or four lenses it replaces can be between 500 and 1500 gms depending on their maximum apertures. It's true that most zoom lenses are "slow" when compared to most fixed focal length lenses. But how often is a 50 mm f/1.4 lens used at f/1.4? Or a 28mm f/2 lens at f/2? The main advantage of these wider apertures is the brighter image produced in the camera viewfinder, giving the fixed focal length lenses the edge in poor light. And be aware... many modern zoom lenses are very compact so if you are shooting at the longest zoom position remember that 200mm on an 80-200mm lens is no different to 200mm on a fixed focal length lens. Longer focal lengths magnify the effects of camera movement... so a faster shutter speed, or a tripod, is essential if you want to make the most of the potentially limited performance offered by a zoom... especially a cheaper lens. 10:39:42 PM    comment []