Hello list,
Does anyone know the actual design of the old Kodak Portrait lenses? What shape elements, how many groups, in what order, etc?
Also, could a smaller fomat version be replicated that could be retro-fitted to medium format cameras bodies? Would they still have a similar effect or would the shorter focal length automatically mean a differenmt (and probably not as pronounced) visual effect? Thanks
The only documentation I have (an old article on lens design by Kingslake) indicates that older portrait lenses (pre 1900) were based on the Petzval formula. The earlier version consisted of one cemented (front: double convex and plano concave) and one airspaced doublet (rear: meniscus and double convex); the later had both doublets cemented (front: double convex and plano concave, rear: double convex and meniscus). To attempt a crude drawing: Early: ())| ((() Later: ())| ())) () = double convex )| = plano concave )) = meniscus So, in essence the front doublet didn't change, but the rear doublet was later reversed and cemented. As far as retrofitting old ones for smaller formats, you have to remember a couple things: first, these designs were FAST, upwards of f/3.3, so they were big and heavy, and as such may just be prohibitive to retrofitting. Second, you're not going to change the focal length of the lens by mounting it on another camera. Some crazy 300mm f/4 is still going to be 300mm in FL, but since you'd be projecting the image onto a smaller area, you'll lose much of the softening effect (around the outside) you may desire. Not to mention that you'll probably be forced to use a smaller aperture because of remounting in a smaller diameter barrel, so you'll lose overall softness as well.
Also, since you would be enlarging the result, that will also change the effect.
If you are interested generally in fitting old LF lenses to a medium format body, I recommend the Bronica S2A, which has a dual mounting system (Bronica bayonet or 57x1mm screwmount) designed to allow photographers to adapt their press camera lenses easily to the new SLR, focal plane shutter, and focusing helical separate from the lens with the option of a macro bellows with full view camera movements on the front standard. I've adapted a 24cm/f:4.5 Voigtlander Heliar as well as macro lenses for this system. Info at:
http://people.smu.edu/rmonagha/bronica.html
Look particularly at the sections on "lens hacking."
Chad and David,
Thanks for the information! One point I wasn't clear on however, is that I would actually like to build a smaller format version from scratch. Focal length around 1500mm to 200mm to cover 2 1/4 by 2 3/4.Would the effect of such a focal length be different than the original Kodaks? Compression effect would be different, of course, but how about the visual quality of the softness?
I think it would be different, because DOF would be different and perceived sharpness of the sharp area of an enlarged negative is likely to be different from the perceived sharpness of the sharp area of an 8x10" or 11x14" contact print. It still might be interesting, though.
From the 1952 Kodak booklet "Camera Technique", the 12 and 16 inch f4.5 Kodak Portrait Lenses were merely simple achromats located behind the aperture stop. They are just two glass elements in one group. The shapes of the elements look slightly unusual to me: the front surface looks to be flat, and probably as a consequence the cemented surface is rather steeply curved.
It would be easy to play with a similar design. You could try the using an objective lens from a binocular. Surplus Shed, http://www.surplusshack.com/, frequently has lenses that could be tried for a purpose like this. The biggest difference I see from trying this on medium format is that you would be enlarging the negative and so the final image will be visually softer than the image on the negative.
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