Archived posting to the Leica Users Group, 2005/12/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Long lenses require humongeous stability. Trust me on this, as I have gear which can work out to 2600mm or more without much effort, and I can approach 10,000mm with a few extenders and adapters. There are several tricks to this. First, there are three kinds of long lenses: long-focus lenses, telephoto lenses, and catadioptric lenses. The first are simple telescopes used as camera lenses, and is the approach favoured by Max Berek and his immediate successors at Leitz. Thus, a 200mm lens will be eight inches (200mm) long, no more and no less. The second type use optical compression, which results in a shorter lens but with some optical compromise: this was the solution favored by Zeiss as can be shown by comparing a 4/135 Zeiss Sonnar with a 4.5/135 Leitz Hektor and note that the Zeiss lens is substantially shorter. The third solution uses a mixture of lenses and mirrors and involves a number of optical designs ranging from the Ritchey-Chretien and the Dall-Kirkham through a few lesser-known designs, some of great merit, to the better-known Schmidt and Maksutov/Bouwer designs, all of which are compact but all of which produce off-focus "donuts" offensive to some. All of these designs involve compromises between weight, length, and optical performance. My favorite long lens is my second-generation 5/40cm Telyt, a lens which I find astonishingly sharp and quite contrasty. It is long and heavy, and hard to use. I love my 1300mm Questar but, again, it is heavy, though it is a dream with a Visoflex in focusing ease and optical performance. I love my 4/300 Kilar but this, again, is heavy. I even use my Swift 831 76mm refractor on occasion as a long lens, and, yes, it functions well. But you need HUGE mount stability: that optical axis mandates this. You CAN use a 300mm lens hand-held at high noon with fast film, but only if you are stone sober and can brace yourself well against a wall. You cannot do this with a longer lens, and don't waste the effort and our declining stocks of film <he grins> to discover this for yourself. The ETX 70 is a decent telescope and a decent lens, but it needs the respect its long optical axis mandates. It is not an especially exciting item either as telescope as lens but is capable of fine results if used carefully and with respect for the demands it places. Long focus photography can be most frustrating as this requires not only extraordinary care and effort but also as it makes one a hostage to ambient weather conditions. Air temperature rules: if the weather is cold outside or hot, you have to let the lens acclimatize for an hour or more to adapt to the outside temperature. And when yuu are done, you have to be cautious about taking the gear inside: if the outside air is hot and humid, taking it inside to a dry, air-conditioned environment can be a problem, and the converse during winter months can be even worse. (The solution is simple: acclimitaze by allowing the lens to sit inside on a table without any caps on it for an hour or more to allow any humiidity effects to disperse.) Long-focus photography is frustrating but it can be rewarding. Just be cautious, careful, and do not expect more from the gear than it can deliver: an ETX 70 is a mass-produced optical item capable of good results but it requires some loving attention to produce such results. Marc msmall@aya.yale.edu Cha robh b?s fir gun ghr?s fir! NEW FAX NUMBER: +540-343-8505