Bodging lenses

Lenses are marvels of optical calculation and manufacturing craft. So why am I futzing around with old projector lenses and door viewers?

Part of is the joy of orneryness (easy for you to say): the pleasure in solving a problem by going against the grain and taking the less obvious path. Yes, I could spend the kids’ inheritance on eBay and buy a Meyer-Goerlitz lens with magical bubble bokeh. Or I could wrap an old slide projector lens in camping-mat foam and jam it up the middle of a set of extension tubes. There are some fantastic and rare macro lenses out there, but you could also pop an enlarger lens (which is usually well corrected for macro work) on some form of extension tube or bellows.

Something I have been looking at is the Petzval lens. I didn’t know they existed until Lomography started selling them. Nice results, even if you wouldn’t want to use it all the time. A lot of money to put out for something that would spend most of its time in the bag, though. Plus they don’t make them in either of the lens mounts I use. You can get old brass lenses that were made with the Petzval design on eBay, but they too have shot up in price. But the Petzval formula is pretty simple and some projector lenses use it. So I’ve been looking at old projector lenses but also thinking about building my own. There are places that sell lens elements in various types and strengths, so I’ve been tinkering with the maths to find a combination that works. By works, I mean can be far enough away from the film or image plane to allow for the depth of the camera body plus some means of focusing. This sets limits on the focal length of the lens, which in turns sets limits on how wide an aperture I could get.

My camera has a lens flange to focal plane distance of a gnat’s less than 46mm. So, without clever lens designs, the widest focal length I could use would be 46mm. At the long end I’m limited by the diameter of the lens elements I could find. It’s all very well building a 500mm lens, but not if it only works at f22. I might lose that swirly background I was working so hard to obtain. Besides, a long lens would turn into a ridiculous bazooka pipe. So I’m looking in the 80 to 150mm range. Focusing is not really a problem, as I have some magic focusing bellows left over from an earlier infatuation. On the other hand, life is short (and ars longa, even with support pants) so I will probably stick with bodging existing lenses.

Some years ago I was reading an article on Elliot Erwitt and his candid street photography. He was said to use an unusual lens combo: a longish manual lens mounted on a set of macro bellows. The lens was long enough to give a proper infinity focus and the bellows had a rack and pinion to focus. The bellows also meant that he could go from long shot to close-up without changing anything. So like photographers immemorial, I bought the kit to improve my pictures. This was when you could buy all sorts of accessories from Practika and Zenith at almost pocket-money prices.

bellows

Actually, it worked. With a 4″ enlarging lens on the front it really did cover a wide range at the expense of manual everything. So the bellows would be my focusing rack for further experiments. It didn’t work for slide projector lenses though. These were too wide to fit into the front of the bellows and the bellows wouldn’t shrink down enough to give an infinity focus. No problem, as bodging baffles brains. Along came a set of very cheap manual extension tubes from China. Then a layer of camping mat foam was wrapped around the lens using gaffer tape, until the lens was a snug fit inside the tubes. Then I had a lovely soft focus portrait lens that worked really well, as long as I didn’t point the camera downwards. The nice thing though is that it works for a whole range of projector lenses. If I need a longer flange distance I just add a couple more bits of extension tube.

proj 1

For anyone who is interested, the 150mm appears to have smooth bokeh while the 85mm looks like I could get some bubbly bokeh out of it.

Wide angles are a problem though. Proper wide angle lenses overcome the problem with the camera flange distance with clever optics. My 15mm lens can’t be 15mm away from the film or sensor due to the depth of the camera body and the need for a swinging mirror. The clever lens fairies in Japan made it work at a flange distance of around 46mm. But if I want to bodge something wide out of inappropriate parts that flange distance is the wasp at my picnic. And then I read an article on t’interweb… (which I have been searching for ever since). The idea is to use an extremely wide angle CCTV lens. Mount this on tome form of extension tube so that it would focus on a sensor, but leave the sensor as empty space. (OK, just mount the lens on a tube). Then mount this whole thing on the end of a reversed lens attached to a camera. The idea is that the virtual image focused by the CCTV lens is seen by the reversed (strong macro) lens and focused in turn onto a real sensor of film. And if I did the maths right, the macro lens would enlarge the virtual image from the CCTV lens to cover the camera sensor. Plus, a fisheye lens for a CCTV camera is not big bucks. Plus I could test this with my existing lenses before even buying a CCTV lens.

So I did the logical thing and experimented to see if it would work before I bought anything. Mount a lens in reverse on a camera and then hold another lens in front of it to see if I can focus any sort of image. All I got was a very good look at the dust on the second lens. I’m either missing something or the whole idea is daft. I do wish I could find the original article.

But in the meantime I have a couple of useful portrait lenses, a very close-focussing portrait lens and a huge glass condensing lens from an old overhead projector. I’ve been playing with the latter by taping it to the end of a cardboard tube. It’s got a focal length of around 330mm but I could shorten that by putting a magnifying lens between it and the camera.

I’ve also got a 9 diopter closeup lens that looks like it might be a doublet rather than a single element, so might be better quality. This particular one has a focal length of 115mm so fills-in the gap between my two projector lenses. The right size of step-up ring should mount this on my bellows. Or this might be the lens I use with the OHP lens to reduce the focal length. Decisions, decisions…

Go me! I’ve got more lenses than a Fleet Street pro (do they still exist?). There are people who pay good money for this sort of fuzziness.

Author: fupduckphoto

Still wishing I knew what was going on.

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