jeudi 18 novembre 2004

Lenses I've Looked Through 500mm f/8 Reflex-Nikkor The first 500mm Reflex-Nikkor was announced in August 1961 only two years after the launch of the revolutionary Nikon F system. The lens was a monster due to the extremely fast aperture of f/5 - which actually made it too unwieldy for most users. Weighing in at over 1.7 kilos and with a closest focusing distance of 15 metres (49 feet) the lens always had to be used on a tripod and was only suitable for photographing distant subjects. Focusing was done via a knurled ring on a smaller diameter tube behind the lens - while the lens was supplied with five dedicated 39mm filters (L39, Y52, 056, R60 and ND) one of which always had to be mounted in the optical system to maintain accurate focus. Production of this 500mm f/5 lens continued until the end of 1970, but it was concurrently superseded by a much lighter - although slower by 2/3rds of a stop - f/8 Reflex in late 1968. This new lens was to be the basis of a line of 500mm Reflex-Nikkors which are still in production today [not as of 2005]. The notable operational advantage of the first 500mm f/8 Reflex-Nikkor was a substantial reduction of the minimum focusing distance to 4 metres (14 feet). The weight was reduced to 1 kilo thus making the lens just suitable for hand-held photography. In 1974 the lens was upgraded with coated elements and designated as a Reflex-Nikkor "C". Ten years later, and in time for the 1984 Photokina exhibition, it was completely redesigned as a "compact" lens. The weight dropped to 840 grams and, more importantly perhaps, the minimum focusing distance was reduced to just 1.5 metres (5 feet) in "macro" mode with a reproduction ratio of just over half-life size. The terminology for this type of reflex lens varies in magazine articles and conversation. Some writers call them mirror lenses, while others refer to them as "cat" lenses. Cat is short for catadioptric, which defines an objective using both refracting (glass) and reflecting (mirror) elements. The first reflecting lenses were used in telescopes in the 17th century as an alternative to conventional long-focus telescope optics. The first catoptric mirror lenses for camera use appeared as early as 1840 for Daguerreotypes, although the fast and newly introduced Petzval lens superseded them soon afterwards. In early telescopes the single mirror reflecting surfaces worked quite well because only the centre of the mirror was utilised for image-forming star examination. However, for photographic use, higher quality than simply "good central definition" was, of course, required and glass lens elements were added to the construction; thus catoptric became catadioptric. The first catadioptric lens, as we know it today, was made in 1874. It used two mirrors and glass correction elements to fold the light path back on itself twice. Image-forming light passes through the front glass element of such a lens, is reflected by a rear-mounted doughnut-shaped mirror to a smaller mirror cemented inside the centre of the front glass element, and back through a group of glass elements mounted in the centre of the rear minor. So, whereas a simple long-focus 500mm lens is nominally 500mm in length, a reflex (or mirror) lens is about one third of that... a compact 150mm or so in length. In fact, the optical construction of the latest 500mm Reflex-Nikkor (including the rear filter, which is part of the optical formula) is a mere 115mm in length... in other words, less than one quarter of its focal length. The design advantage of a reflex lens is that only a small amount of movement of the focusing mirror is required to provide a considerable focusing range. The design limitation, though, is that they have a fixed aperture because an adjustable aperture cannot be fitted. Typically, 500mm lenses have an aperture of f/8, whereas 1000mm or 2000mm reflexes are fixed at f/11. It is this fixed annular aperture in the mirror that produces the characteristic doughnut effect when out-of-focus specular highlights are part of the image. The effect is often used to advantage by many photographers who purchase a reflex lens. On the other hand, some people don't want the effect - sports or nature photographers, for instance - and so choose a conventional telephoto lens instead. This will also give the advantage of a wider maximum aperture and so will produce better results in low-light situations. But for the enthusiast on a budget, or the creative photographer looking for such image-enhancing effects, a reflex lens is worth considering. I've used the Nikon system for over 35 years and during that time I've never been without one. Although the 500mm isn't a constant companion, as a 20mm or 24mm wide-angle lens would be, the Reflex is always on standby when there's a good chance of including water and reflected sunlight in the picture... for it is the combination of these two elements that makes the lens so fascinating to use. My favourite reflex image is of one of my daughters playing on the seashore (above). It was taken over 25 years ago and has been published at least once every year since in magazines and calendars throughout the world. It is, therefore, worth calculating the earning potential of a lens such as this when considering a purchase. Even at relatively modest reproduction rates, it can be seen that a specialised lens purchase, in the right hands and with the right ideas, doesn't become a cost, it actually becomes an investment. In use, the compact 500mm Reflex-Nikkor is very hand-holdable. With the camera firmly gripped in the right hand and ready for exposure, and the tripod-socket part of the built-in tripod ring nestled in the palm of the left hand, the lens can be easily focused with gentle rotation of the broad focusing ring between left thumb and forefinger. The focusing ring is well-dampened, unlike many AF lenses today, and has a travel of approximately 460 degrees (one and a quarter turns) from infinity to closest focusing distance of just under five feet. As is common with telephoto lenses, to allow for discrepancies due to the lens barrel and internals warming up in hot conditions and causing alignment problems, focusing extends beyond the infinity mark. As with a conventional telephoto lens, to ensure sharp results, hand- holding the 500mm Reflex should be undertaken with a shutter speed of at least 1/500th of a second. However, to achieve this with an aperture of just f/8 requires a substantial amount of light, so it is probably a lens to keep for brighter days. Because of the lens' fixed aperture, correct exposure has to be adjusted primarily with the camera's shutter speed controls, or by using Aperture Priority mode on Nikons so equipped. In addition, dedicated filters are supplied with the lens, one of which is an ND4 neutral density which cuts down the amount of light reaching the film by two-stops. When using black-and-white film the supplied orange O56 filer can be used in the same way. Two other bayonet-fitting 39mm Nikon filters can be purchased in yellow (Y48) and red (R60) versions, which are both useful to the creative monochrome photographer wishing to exaggerate sunrise and sunset colours, as well as other special effects. The red (R60) filter is also useful for infrared film work, although the lens itself does not have, or need, an infrared focus correction mark because the mirrors in reflex lenses - like Nikon's ED (Extra-low Dispersion) glass - do not suffer from the focus shift of ordinary glass elements. The 500mm Reflex-Nikkor is actually easier to focus manually with a Nikon autofocus camera because of the brightness and clarity of modern focusing screens. Manual focus cameras are normally supplied with the traditional split-image focusing screen which blacks-out when used with any lens slower than f/5.6. With manual cameras the Nikon Type B (Matte/Fresnel with Spot) and E (Matte/Fresnel with Spot and Grid) screens are recommended if available. In conclusion, if you are the type of photographer who looks for something different in your images, then the Reflex-Nikkor is certainly a lens for your bag. You have to learn how to use it to get the best from it, though. Focusing on a nearby subject surrounded by specular highlights will produce the best effect as seen in "Sea Sprite" image, where the highlights on the waves and ripples in front of and behind the youngster took on the pronounced doughnut shape. With subjects further in the distance there is not so much out-of-focus on either side of the main subject so the lens responds more like a normal telephoto without the accompanying visual effects. There are few photographers with undecided opinions on mirror lenses - they either love 'em or loathe 'em - but I certainly couldn't be without mine! BTW: If you want the most up-to-date Nikon news, reviews, tests, downloads, folios and opinions Nikon Links will have them listed and checked out. 7:48:35 PM    comment []