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500mm f/8 Reflex-Nikkor (2)
Optical contortions...
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 center of the front glass element, and back through a group of glass elements mounted in the center 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.
How high on the wish list?
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 almost 40 years and for the latter 30 years I've rarely been without one... for those creative moments with a difference. 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 favorite Reflex lens 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 specialized lens purchase, in the right hands and with the right ideas, doesn't become a cost, it actually becomes an investment.
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