Need help identifying lens (once more)

Having been so succesful in the past with asking questions like these here on APUG, I now call again on all you lens buffs to help us out with nailing this recent acquisition to our lens stable.

Yesterday on the fair we have found what seems to be a wide angle lens, with a fixed iris opening and a built-in yellowish green filter. Focal length roughly between 160 and 162 mm. Smallest f-stop of roughly 5.6. No signs/markings or anything that would help the research. Large image circle, fills out 4x5 with plenty of movements, approx. 19 cm Ø. Size of the lens barrel:Ø53mm and 56mm long.

The lens is a lot smaller and lighter than an aero-ektar, but we think that it must have been some kind of aerial lens (due to the presence of the yellow filter), or some kind of industrially used lens.

We haven't taken it apart yet, but we plan to take out the filter and insert an iris. Mounting in a shutter isn't a priority, having a lot of gear with curtain shutters, but it would be an option.

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The fair itself was busy and pleasant. Unfortunately not enough large gear to our taste. One 13x18 studio view camera, some smaller ones. Some older cameras (turn of the century) that were bigger, but nothing that made us want to bleed cash. Same situation in the old lens dept. And no affordable size 0 Synchro Compur for the G-Claron either .
Instead, we stocked up on lens caps (1 euro a piece, even the Schneider ones!), found some other bits and pieces, a near new 180m 4.5 Tessar for 20 euros that neatly fits the Optika extented lens board tube, a nearly complete Arca Swiss compendium for the Pecoflex for 15 euros from a nice Englishman, some ADOX 126 films for the Rollei SL26 (finally a chance to use this camera which is awaiting serious modifications).

A happy surprise was to see relatively many young people in the crowd, kids with huge Mamiya RZ's in their hands, with looks intended to coax money out of parental wallets, a read head girl trying out a Rollei SL66, two boys in conversation over dark room equipment, etc. etc. It wasn't like that half a year ago. The tides might be turning here as well.

medform-norm said:

Having been so succesful in the past with asking questions like these here on APUG, I now call again on all you lens buffs to help us out with nailing this recent acquisition to our lens stable.

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Okay aerial lens buffs, I'm going to give some hints. Maybe that helps?

The lens design is a Wide Angle Gauss, aka Q17 in the LVM. Four air spaced elements. Focal length is probably 160 mm (rather than 162mm). Largest opening is calculated at 5.6. Fixed f-stop was at f7. The yellow filter was not attached to the lens, but indeed a separate filter screwed in and now removed to a better place.

We expected the lens to be sharp all over. However, we notice a fall-off in sharpness at the corners. I mean, when the corners are sharp, the middle isn't - and vice versa. Is this common in a Gauss type lens? Or does it mean we've got a cheapo version (admitted, what can one expect for 5 euros, eh?).

So, who'll take a shot at telling me what we've got?

You have me stumped, but only temporarily. I'm sure I can get close as soon as I get home - unfortunately I can't bring my library with me to work here in the North Sea.

Sometimes even knowing what it is doesn't help, you're still left guessing. A case in point is my 500mm f:5.6 Schneider Göttingen Aerotar. Schneider didn't make it; ISCO did. ISCO has no records. It's different to the Goerz Aerotar - very different.

ISCO was part of Schneider, established to build military stuff.

Somehow, your "ISCO built military stuff" and Oles "ISCO has no records" makes perfect sense together.

There is a chance that our lens is former military stuff as well, it has no markings anywhere.

What we find so odd about it, is that it seems to have been used for aerial stuff, yet it's so very small and light compared to other known aerial lenses. It doesn't weigh more than a simple Symmar. Not that I'm complaining about having such a light weight lens...

We'll just have to start shooting with it as soon as we procure some kind of iris for it. Or maybe we should make Waterhouse stops for it. Anyone know anyone who's done this before - and if so, how it's done?

medform-norm said:

We expected the lens to be sharp all over. However, we notice a fall-off in sharpness at the corners. I mean, when the corners are sharp, the middle isn't - and vice versa. Is this common in a Gauss type lens?

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What you're describing is classic field curvature -- which, in aerial cameras, was commonly dealt with by curving the film, just as in some cheap box cameras. Seems to me this was common in a Gauss, though it should be much less noticeable as you stop down.

medform-norm said:

We'll just have to start shooting with it as soon as we procure some kind of iris for it. Or maybe we should make Waterhouse stops for it. Anyone know anyone who's done this before - and if so, how it's done?

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Waterhouse stops are easy if you can slot the lens barrel between the middle elements; just drill a hole in sheet metal (brass or copper are relatively easy to blacken, or steel can be blued with a commercial product available in gun stores) to the correct size, calculated from the lens focal length. Drop the correct stop into the slot; they're easier to remove and identify if you leave a tab on the disc, on which you can stamp or engrave the diameter and f ratio. Being perfectly round, they produce nice bokeh, too.

Exact placement would require some optical calculation to determine the position of the internal node, but most lenses will tolerate considerable error in location, so it's probably fine to center the stop between the middle elements.

df cardwell said:

ISCO was part of Schneider, established to build military stuff.

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Correct; it was "Schneider Göttingen" for a few years. They found out my lens was made in 1944 - and the factory was bombed shortly after. And that's why there are no records.

Any aerial photography lens made in 1944 is very likely to have been military, and a 500mm is likely to have been made for high-altitude photography. Make sense?

My lens, BTW, has all the usual markings as well as a bayonet-fitting yellow filter and a velvet pouch

Donald Qualls said:

What you're describing is classic field curvature -- which, in aerial cameras, was commonly dealt with by curving the film, just as in some cheap box cameras. Seems to me this was common in a Gauss, though it should be much less noticeable as you stop down.

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Donald, where did you get the quaint notion that aerial cameras have curved film planes?

Norm, the typical 4-element w/a double Gauss lens doesn't suffer from field curvature, it suffers from aperture-related aberrations whose effect diminishes on stopping down. That's why, for example, TT&H recommend that the legendary f/6.5 Cooke Ser. VIIb not be used at apertures larger than f/11.

Norm, to get back on topic, aerial camera lenses used by the allies during WWII usually had diaphragms and ones as short as 160 mm +/- were usually faster than f/7. The only WWII German aerial camera lens I've had the pleasure of handling was a 125/2.5 Schneider Goettingen Xenon. stopped, IIRC, to f/22.

You might have a Metrogon. Many of the ones I've seen have been without diaphragm or shutter. The 6"/5.6 Metrogon was made to cover 9" x 9" on 10" film. Donald, the film comes in large rolls, is transported straight across the gate.

It could have been a lens for air-to-air photography: they tended to be more 'normal' in aperture and design than the ground observation lenses. There were also recording cameras used with intervalometers for bomb damage assessment and torpedo tracking which tended not to have the huge beast lenses fitted.

I found this the other day while looking for Aviars on the web:

"Some Precision Problems in Air Survey" Lt Hotine RN, 1925

Interesting for aerial buffs.

Ole, a lot of the photographs taken by the Luftwaffe ended up in the UK. I think they are held at the Imperial War Museum (if not, the British Library can held you find them). Staff there might be able to help you with info on cameras and lenses.