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Tadge Dryja
26-Oct-2003, 17:54
Does such a thing exist as a telephoto mirror lens for large format cameras?

I like using fairly long lenses when using 35mm cameras, and it seems that in large format there is something of a shift twoards wide angle lenses. I don't know how many are actually sold, but it seems like there's much more discussion about 100mm and below lenses than 400 and up. I've never done anything bigger than 4x5 and don't really plan on it, but even like a 300mm lens still is kindof short.

So there are lots of pretty cheap mirror lenses for 35mm, usually around 500 f/8, and they're pretty light and small. I think because of the design you can't have an iris, so it's f/8 all the time. So has anyone ever seen something like a 1000 f/11 or something miror lens for a 4x5 camera? Could such a thing even be produced? I don't know nearly as much as I'd like to about optics, maybe the different nature of mirror lenses would wreak havoc on any shifts or tilts you might try, .. and would you need a lot of extention, or would it act like a telephoto design lens?

I'm asking mostly because my brother got a big telescope that uses mirrors (a meade LX-something) and so it seems that mirror lens designs are well suited to long lenses.

Thanks for any info!

-Tadge

David A. Goldfarb
26-Oct-2003, 18:58
There are telescopes in observatories that can record observations on sheet film or glass plates, but these aren't terribly portable.

Frank Filippone
26-Oct-2003, 19:07
In years past, I had heard that Zeiss mirror lenses ( Mirrotar?) would cover 6x6cm. Not exactly LF... About the largest coverage I have heard about......

As someone noted, there is the astronomical telescope, and of course the Hubble telescope that also would probably cover, but getting the CFH changed would be a bit tedious.

Ernest Purdum
27-Oct-2003, 10:55
A mirror lens for LF would be possible, but I doubt very much if the result would be worthwhile. There are two problems, one relating to mirror lenses only, the other pertaining to any telephoto lens.



Mirror lenses lack the ability to use a normal iris. This is not much of a problem for 35mm, but for large format, depth of field more often than not requires stoppping down, particularly for long focal length lenses.



Rise, fall and shift movements are no problem with a telephoto lens, but the results if you try to use front tilt or swing are downright weird. The "pivot point", (rear nodal point, actually) of your lens is way out in front of the camera. Instead of merely changing the plane of sharp focus, tilting shoots the image right off the groundglass. Telephoto lenses have their purposes in large format work, but are rather specialized and my impression is that the market for such lenses is rather small, probably too small to allow for the development of a lens which would be even more specialized then those now available.

Michael S. Briggs
27-Oct-2003, 21:12
I don't think there is much demand for really long lenses for LF work. Even in 35 mm, really long lenses tend to be used for specialized areas such as wild life or sports photography, areas ill suited for LF photography. (Though photojournalists used to use Speed Graphics for sports photography.) For 35 mm photography, roughly 180 is about the limit for general pictorial photography. This focal length corresponds to 630 mm in 4x5. There are many 4x5 cameras that have sufficient bellows for a non-telephoto 450 mm lens, and even for the 720 mm Nikkor-T telephoto lens. So I think the manufacturers have provided for about the longest lens that most LF photographers will want. Nikon even makes a 1200 mm Nikkor-T.

There are threads in the archives about using long lenses. Vibrations are a problem and many who try this use two tripods.

Most cadioptric lenses have fairly large diameters. One for LF probably wouldn't fit through the throat of most LF cameras and so would have to be mounted in front of the lensboard -- the heavy lens would have quite a lever effect that would overwhelm most LF cameras.

The ultimate cadioptric is a Schmidt telescope/camera. Compared to most telescopes these have relatively large fields of view. The most famous is the 48 inch (122 cm) Oschin Telescope at Mt Palomar -- see http://www.cr.nps.gov/history/online_books/butowsky5/astro4f.htm. The dimension 48 inches is the useful aperture, not the focal length! This used glass plates up to 14 inches square to image 6.6 degree square sections of the sky.