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  1. #1
    ausphoto's Avatar
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    Massive Gauss Type Lens to be identified !

    Hi all,
    Any idea what this is/where it might be from?
    It's a double-Gauss lens with eight elements in six groups

    http://www.flickr.com/photos/heritag...es/5017011205/

    and what are the holes for..as if the lens had to be kept cool...or warm..

    help is much welcomed!

  2. #2

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    Dirk, are you sure it is assembled correctly and that your cross-section is correct? I ask because lenses with an, not to mention both, outer elements concave outwards are really quite uncommon.

    Does it form an image? If so, what is its focal length, more-or-less? I ask because I have some USAF data sheets that might shed light. They're ordered by focal length, so I'd like to know roughly where to dive into them.

    There's nothing like it in 1963 GOI catalog's generic cross-sections at the front; if you don't know this catalog, you can download a copy from http://www.lallement.com/pictures/index.htm, look in "files."

    There's also nothing like it in Eric Beltrando's catalog (www.dioptrique.info, if you don't know it), but he's interested mainly in older designs.

    The holes make no sense at all.

  3. #3
    ausphoto's Avatar
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    Hi Dan
    Many thanks for the comprehensive reply. ok..

    The lens is assembled the way I got it..just cleaned (still some issues but nothing that I can deal with easily and readily)
    The lens does provide an image. I propped it up on a bucket as my arm was too short/the lens to heavy at that extension and used a tape measure...

    The length at which the image (an object more than 15m away) does not seem to improve in sharpness is around 31-32 inches..about 785mm...Given the diameter of the front element (4 7/8in), a 31inch length gives me 6.35....so lets assume it to be a f6.3 / 31 inch lens ... unless I made a calculation mistake somewhere...

    The holes must be for airflow, to either keep the lens from fogging or from overcooling or overheating...
    Last edited by ausphoto; 09-23-2010 at 04:49 PM. Click to view previous post history.

  4. #4

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    Dirk, the monster is probably mis-assembled. Chances are that the outer meniscii are reversed, they should probably be convex outwards.

    I was reminded of Brian Caldwell's existence today. I don't have a copy of his database Lensview -- too expensive, not needed for taking pictures -- but at this moment wish I did. The design might be in it. Suggest you track him down and ask his opinion.

    Re the holes, I've seen a fair number of aerial camera lenses in the metal and glass and in catalogs. No Swiss cheese there. I've also seen stepper lenses as used in chip fabrication, no Swiss cheese there either. Yes, I have some of both and no Emmenthaler in the house. Other cheeses, yes, Emmenthaler, no.

    Aerial camera lenses sometimes have heating tape around the middle or a grid of resistance wires in front, both to chase the dew. I don't know whether lenses that flew in self-heating aircraft such as the SR-71/A-11 were cooled. I used to work with an ex-SR-71 pilot, lost track of him years ago so can't ask him.

    The thing gives the impression of being an, um, poisoned gift. It has at least that in common with many aerial camera lenses.

    Good luck, have fun,

    Dan

  5. #5

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    Quote Originally Posted by Dan Fromm View Post
    Dirk, the monster is probably mis-assembled. Chances are that the outer meniscii are reversed, they should probably be convex outwards.
    Why?

    My first guess: a projection lens.
    Holes to give the heat somewhere to go.

  6. #6

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    QG, I'm aware that at least one version of Voigtlaender's Ultron (IIRC, might have been a Septon) has a front element that's concave outwards. This configuration is very uncommon. It appears -- the sketch might not be quite correct -- that the monster's outer meniscii will fit facing either direction; convex or concave outwards.

    There are a fair number of double Gauss variants with the outer meniscus split. I just took a quick look in the VM and a couple of Soviet sources, found a number of such lenses, none with the outer element(s) concave outwards.

    It could well be assembled properly, but it doesn't have to be.

  7. #7

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    The fact that this configuration is rare does not mean it is wrong. Nor that it is more likely to be wrong than correct.
    If we would assume that sort of reasoning, anything rare should really not exist.


    Not that i know whether the way the cross section is drawn is or is not correct.
    But the fact that it is rare alone does not allow to draw conclusions yet.

    Nice 'puzzle' though.

  8. #8
    ausphoto's Avatar
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    ok. The cross-section is drawn exactly the way I found it. I fully measured it all out too.
    It is of course possible that the end menisci were flipped to allow for safer (not scratch) storage as nothing would protrude. However, the way the outer lens retaining ring is fitted, it does not look as if it would allow a snug fit if the meniscus were reversed. But I will that check later today.

  9. #9
    ausphoto's Avatar
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    just tried it...yes, one can reverse both outer meniscus units and achieve a snug fit with the retaining ring...
    http://www.flickr.com/photos/heritag...es/5018936535/
    the resulting image seems a tad crisper that way too... I will rig up a tripod set over the weekend and see what can be done to document this...
    Last edited by ausphoto; 09-23-2010 at 11:04 PM. Click to view previous post history.

  10. #10

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    Quote Originally Posted by Q.G. View Post
    The fact that this configuration is rare does not mean it is wrong.
    Fair enough.

    Quote Originally Posted by Q.G. View Post
    Nor that it is more likely to be wrong than correct.
    If we would assume that sort of reasoning, anything rare should really not exist.
    Whether the lens is assembled correctly is an empirical question. That said, the odds (many many published cross sections of double Gauss derivatives with outer elements convex outwards, few with an outer element concave outwards, none with both outer elements concave outwards) that it is not assembled correctly are high.

    Note, however, that the cross-sections I have access to are of lenses designed before around 1970. High performance wide angle lenses designed since then look a bit strange relative to older designs, this may be true of high performance narrow angle lenses too.

    I didn't assert non-existence, I asserted low probability that it is correct. There's a difference between the two.

    Dirk, your images seem to show no diaphragm. Is there one?

    FWIW, Dirk, I have an ex-USAF 36"/8 B&L telephoto doorstop whose cells are held together by a sort of clamp. No shutter, no diaphragm, and the cell spacing might but need not be correct. Anyway, my lens is clearly incomplete, makes me wonder whether your monstrosity is complete and its cell spacing correct.

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