Massive Gauss Type Lens to be identified !

Dan Fromm

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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.
 
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ausphoto

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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...
 
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Dan Fromm

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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
 

Q.G.

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Dan Fromm said:
Dirk, the monster is probably mis-assembled. Chances are that the outer meniscii are reversed, they should probably be convex outwards.
Click to expand...

Why?

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

Dan Fromm

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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.
 

Q.G.

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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.
 
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ausphoto

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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.
 

Dan Fromm

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Q.G. said:
The fact that this configuration is rare does not mean it is wrong.
Click to expand...

Fair enough.

Q.G. said:
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.
Click to expand...

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.
 

Q.G.

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Dan Fromm said:
I didn't assert non-existence, I asserted low probability that it is correct. There's a difference between the two.
Click to expand...

Which is my point.
Probability, whether high or low, says something about our expectations. Not about the thing we have those expectations about.


It would be fun to see a series of test images made using this lens, in all configurations.
 
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ausphoto

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Dan
No, no diaphragm and the mechanism doesn't allow for one either it seems.
The lens mount (which is cast!) has threads into which the two units screw into....the lens spacing as shown in the diagram is correct as far as right and left units are concerned. Spacing of the two main units to each other is correct within 1/4 inch. I am not sure how the whole assembly was mounted, and whether it was encased, and how. The retaining rings at the ends of the lens are well made and there is nothing missing there.

Given that the serial number was CAST with the lens mount, there must be quite a few of them. The recurrent serial is 1095-18xx, with the individual pieces then labelled with scratched in numbers.
 
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ausphoto

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Q.G. said:
It would be fun to see a series of test images made using this lens, in all configurations.
Click to expand...

YEs it would, but that would require to make a camera just for it.. When I have the time, hopefully this weekend, I'll mount the lens on a tripod and then photograph the image on the lens in both configurations. And if I get bitten by the bug, I might just make a lens cone out of cardboard and a simple frosted screen...just to work out which area the lens might cover.
 

Dan Fromm

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Thanks for the additional detail. Aerial camera lenses were made with fixed apertures. I have a 3"/4.5 Biogon type that has a shutter but no diaphragm. And some were made with cast barrels.

I'm not sure how to tell how many examples of a lens were made. The s/n smells like an Elcan one. These have the form tttt-nnnn, where tttt is the lens' type and nnnn is the individual lens' sequence number. There's no type 1095 in my Elcan C-series reconnaissance lenses catalog, but this proves nothing.

I'd been doubting that its an aerial camera lens because it seems to have come apart easily. The ones I've had (1 Ross, 1 S.F.O.M., 1 LOMO, 3 Elcan, 3 TTH, 20 Zeiss) were all made to be hard to disassemble. This to resist vibration. But again, if yours came apart easily that proves nothing.

Cheers,

Dan
 
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ausphoto

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The epi(dia)scope option is certainly something to be followed up. I have trouble finding lens sections of the lenses, though. It clearly isn't a Leitz...

The problem is that the lens mount of the unit I have in hand does not have a focusing helicoid, which is required to focus the projected image (as a student in the 1970s I used these monster devices to project pages from books for discussion in tutorial presentations). It looks more like a fixed focus unit.
And all cinema projection lenses (which would have a fixed projector to screen distance once installed) I can find are smaller..

Also, all projection lenses I have seen, although exposed to the heat of the lamps, don't have these weird holes...

I have been toying with the idea whether it could be an 'eye-piece' of a very large telescope, but all the cross-sections i can find there are also different...
 

Dan Fromm

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Absence of a focusing helicoid is consistent with a naked (out of its cone) aerial camera lens. I've seen two ways of collimating aerial camera lenses to the camera.

The lens screws into a mount called, by convention, a lens cone, is screwed in or out to collimate and is then locked in place; examples that I've seen include Vinten F-95; AGI F134, F139, and Agiflite; and Omera 31. The cone is bolted to the camera body or bayonets into it.

The lens (in shutter) is bolted to the camera main casting, shims between body and back of shutter adjust flange to film; this is how the 38 Biogons in the AGI F135 were collimated to the camera.

Thanks for the link. Some time ago I wrote an essay in which I characterized most aerial camera lenses as poisoned gifts. I think that fits the 7"/2.5 Aero Ektar adapted to M42 mount shown in the link.

Anyway, I agree with the person who responded that the holey lens shown in that thread is part of a condensor. It has the look, and I'd swear I've seen similar things offered as condensor lenses. Your monstrosity doesn't. Could be mistaken, though, about the lens in the link. I don't believe that condensor lenses are often as elaborate as the monstrosity.

Why do you think that Leitz bought in lenses for their Epidiascopes?
 
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ausphoto

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Dan Fromm said:
Why do you think that Leitz bought in lenses for their Epidiascopes?
Click to expand...

Dan, I didn't. What I meant to say is that mine is clearly not a Leitz...

Need to see other epidiascopes (sections or originals) and look at their lenses. But most of the old units seem to have been thrown out by the universities and schools...
 

Q.G.

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Ask any LF photographer, and you'll be told that absence of a focussing mount doesn't mean the lens is meant for fix-focus use.


(I'm not saying, by the way, that it is an LF lens. Just that a focussing helicoid is not the only way to focus a lens).

Holes in the lens could really only serve one purpose: cooling or heating.
Cooling would imply great heat, and that you only get in a projection system.
Heating would be used to prevent a lens fogging up, which would fit with it being meant for aerial use.
 

Stephen Frizza

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Im curious I just saw this lens and i was thinking this may not be a projection lens but could this be a small 1940's ground to air war time search light lens? as in for spotting bombers at night?........ my imagination runs wild.
 
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AgX

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Search lights would not need any complicated lens system. All search lights I know of use a huge (parabolical) mirror and a very small mirror to shield the lamp/burner to the front.
 

Stephen Frizza

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I have seen those kind of search lights but i have seen search lights with lens too. though none with a lens like the one shown here. my imagination ran wild because of the holes in the lens.
 
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