Are there any telephoto lenses with only two groups of elements, or must there always be a a third.
The question came up because I looking for an uncoated telephoto that has fewer groups and therefore potentially high contrast.
Are there any telephoto lenses with only two groups of elements, or must there always be a a third.
The question came up because I looking for an uncoated telephoto that has fewer groups and therefore potentially high contrast.
All the large format true telephoto lenses that I own, 5 lenses from 240mm to 500mm, all have their glass arranged into 2 optical groups. One in back of the shutter and one in front of the shutter. Each group may comprise several glass elements.
I would like to add that I wonder if you are just referring to "true" telephoto lenses, or both telephoto and long-focus lenses? A telephoto lens is designed to focus with less bellows draw than the same focal length "normal" lens, thus allowing you to work with a field or press camera which has limited bellows draw. Exactly the same field of view can be had from a normal design lens of same focal length, but would require more bellows draw. If you have the bellows length needed, then probably the most contrasty, snappy images could be produced from a "Tessar" formula lens of conventional design. Thus a 240mm Tessar (for instance) may produce snappier images than a 240mm Telephoto design lens, but would require much more bellows.
Some early Tele-Xenars were 4 elements in 2 (cemented) groups, but others are not. There was also the Dallmeyer Adon, which could be a whole confusing chapter in some book - finding out what an Adon is, and what it's for, seems only to be possible by experimentation (I have two, one is a telephoto lens. The other is a focal length extender for front mounting).
Um, Rider, there are so-called telephoto lenses for smaller formats -- up to at least 6x6 -- that are not teles, just long focus lenses of very simple construction. Achromatic cemented doublets. Two elements at the front of a long tube, the two elements glued together.
Century Tele Athenars and Tele Athenar IIs, Kilfitt TeleKilars, long Novoflex Noflexars, etc. use this design. I used to own a 500/5.6 TA II that I had Century rebuild ($$$) to as-new condition. After the rebuild it wasn't that sharp and suffered from severe chromatic aberration.
Its your time and your money, but I don't think you should want anything like this.
Ole's suggestion of a Adon isn't bad. Or perhaps a TeleRos or a TTH tele. I have one that doesn't fit your requirements, a 12"/4 TTH Tele ex-Agiflite, that the VM says just covers 4x5 and is quite nice on 2x3. Or a TeleRaptar, and live with all of the contrast it can deliver.
I didn't "suggest" an Adon, I just "mentioned" them.
Before you buy an Adon make sure you know exactly what it is; you even risk getting something that isn't a photographic lens at all.
Another old tele lens is the Voigtländer Tele-Dynar. They tend to go to collectors for collector's prices. Finding an old (1930's) Schneider Tele-Xenar is likely to be both easier and cheaper, even if they aren't all that common.
The best option IMO is to find a long "ordinary" lens. Used on 4x5" film, even a 300mm aplanat is likely to be cheaper, contrastier, lighter as well as sharper than a true telephoto lens.
A pre-war tele-xenar might be what I'm after. (btw, I am referring specifically to true "telephotos" since I'd like to have short bellows draw).
I'd read somewhere that the design of a typical telephoto involves the addition of a negative element somewhere. Since most designs have 2 groups to beging with, it seemed unlikely a true telephoto would have fewer than three groups.
At least one illustration of a pre-war tele-xenar showed 3 groups: 2 cemeted doublets with a single element behind them.
Your comment "since most designs have two groups to begin with" sounds like you are thinking of telephoto designs as normal lenses, plus an addition. In truth, this is the way telephoto lenses started out. They were analogous to the "Barlow" lenses use by astronomers, and the focal length doublers common in small format work. By adding an adjustment between the orignal lens and the added (negative) lens, a great range of focal lengths could be provided. These were not zoom lenses, however, as the focus changed any time the focal length was altered.
In 1905, Busch produced a lens designed by K. Martin which had a fixed focal length, the Bis-Telar. In this instance, the whole assembly was considered as one design task. Four elements in two groups were found to be adequate. Both groups had positive and negative elements. Such fixed focal length lenses were found to be preferable in several respects to the earlier variable type which eventually ceased to be made.
Rider, buy a book. Buy several books. Bulletin boards are the wrong place to seek an education, and that's what you need even though I believe you think you want answers to seemingly simple questions.Originally Posted by Rider
All of the photographic optics for complete idiots -- I am one and I have several of them -- explain what makes a telephoto lens. Basically it is a lens with a positive system (converging) in front of the diaphragm and a negative system (diverging) one behind. The systems can contain multiple air spaced or cemented elements, see for example my TTH bon bon.
There's really only one reason to want a tele lens instead of a long focus lens with the nodes in their proper positions. That is when using a camera that doesn't offer enough extension to allow a long lens of normal construction to be focused. Otherwise "normal" lenses win hands down. Teles have worse distortion, less coverage, and make swings/tilts difficult.
Thanks Dan, I do need to learn more from books.
Ole or someone else: the oldest Schneider brochure that I found dates to 1938. What about even older Tele-Xenars, such as the from the 20s? Do they also have 4 elements in 2 groups or just 2 cemented elements?
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