brass? what have i bought?

[rippo]

so i bought my first old brass lens recently, and it arrived today. i have yet to use it, as i've got to mount it first. certainly going to be easier to mount than my homemades, what with the flange and screw holes. piece o cake!

so what is it? seller said no markings except a distance scale, and he was right. it's just an inner and outer tube, with a single lens up front. i see three reflections, so i'm guessing it's an achromat...darn. basically an overbuilt landscape lens.

focal length is about 520mm, which would be impossible to use on my toyo 4x5 if it weren't for the giant proboscis of a tube extension the thing has. no vignetting apparent for this format, but i can't check movements etc. going to be about f/16 or so wide open.

so..what is it? anyone know?

here's the ebay link for some pictures.

http://cgi.ebay.com/ws/eBayISAPI.dll...m=280179254488

[Gordon Moat]

At that price, if it makes any image at all on 4x5 film, I think you are way ahead of the game. Just a wild guess, but I would figure it to be a projector of some sort, though it might have been a telescope. Could you give some indication of lens shape and placement? Perhaps there might be something here that comes close:

http://dioptrique.info/sommaire/sommaire.htm

Anyway, Jim Galli probably has like a dozen of these ... I will leave it to the seasoned veterans to give you a better answer.

Ciao!

Gordon Moat Photography

[Brian Bullen]

Rippo, not sure what you have there but you could combine it with a close-up diopter or some other element to bring the focal length down so it's a little easier to use on 4x5.

[rippo]

i'll give the actual element a closer look when i get home from work tonight. it's just one bit of glass (or more likely two, cemented). i'll report back on the shapes of the glass. it's basically a long empty tube with an element on the end though. no fancy duplet or triplet here.

i could have spent less and built something similar myself probably, at least from an optical standpoint. but then i wouldn't have an old and moldy brass tube. way classier than pvc pipe sprayed matte black!

[Struan Gray]

It looks like the input or output arm from a spectrometer. The lens is used either to focus light onto a slit, or to collimate light that has emerged from a slit before or after bouncing it off a diffraction grating. Given the flange and focussing arrangement, I'd guess the former.

The lenses on these are usually air-spaced achromatic doublets, very similar in design and purpose to air-spaced doublets on refracting telescopes. The performance on-axis will be very good. Off axis things can get funky fast. How good - and how funky - depends on the details of your particular lens.

[venchka]

It looks like the input or output arm from a spectrometer. The lens is used either to focus light onto a slit, or to collimate light that has emerged from a slit before bouncing it off a diffraction grating. Given the flange and focussing arrangement, I'd guess the former.

The lenses on these are usually air-spaced achromatic doublets, very similar in design and purpose to air-spaced doublets on refracting telescopes. The performance on-axis will be very good. Off axis things can get funky fast. How good - and how funky - depends on the details of your particular lens.

That's my guess as well based on a spectroscope from my late fater-in-law's laboratory.

[Mark Sawyer]

If you can disassemble it to where you have a doublet in a short barrel, it might be worth trying. The Imagon and Kodak Portrait Lens are doublets; yours might prove interesting. And as Brian said, you can add a positive diopter up front to get something similar to a Verito formula, though the effect would almost certainly be different...

[rippo]

spectrometer? harumph. that doesn't seem very exotic at all. nice to know what it came from though. probably not much of a bargain then, but it's well in keeping with my harebrained LF philosophy.

it seems to cover 4x5 reasonably well in its current state, no modification needed (at least when i hold it up to a lensboard and view the ground glass). if it seems boring in actual use, i'll try a diopter in front.

the inner tube with the lens element will extend a ways out in front, so i might be able to get some closer focusing than i've been thinking.

thanks all! i'll mount it and post results, but could be a few weeks.

-matt

[rippo]

so i tested the lens.



lens turns out to have a focal length of 530mm! which would be too long for the bellows on my Toyo, if it weren't for the fact that the lens element was at the end of a long tube. i can do infinity and objects about as close as 25 feet before it gets out of hand. and because the lens is at the end of a long tube, it only just barely covers 4x5. the lens is f/16, which makes it an outdoor lens for sure.

this image is of the backyard BBQ grill. i gave the camera some back rise to bring the composition into place, and decided i liked the vignetting.

i accidentally previewed the scan in color, and i got this yellowy tone, and liked it. so i worked with it.

definitely a specialty lens. i adapted to this to my packard shutter arrangement, and then shot on Efke ASA 25 film. apparently overdeveloped in D-76.