Using Ultra-Fast Lenses on DSLR Cameras

Using Ultra-Fast Lenses on DSLR Cameras
The ratio between the focal length and the aperture (diameter) of a lens is called the f/number. The smaller the f/number, the more light is let in. Fast lenses start around f/2.0, and the light let in goes as the inverse square. Compared to f/2.0, f/1.4 lets in twice as much light, f/1.0 four times, and f/0.71 eight times. The fastest camera lenses designed for DSLRs and widely available are between f/1.4 and f/1.2, but lenses as fast as f/0.75 have been made in quantity for special applications, and some of those are available quite cheaply via scrap yards, surplus stores, or eBay.

These ultra-fast lenses usually are branded either Kowa or Rodenstock and were designed for use in medical or semiconductor industry equipment, etc. They are not well-suited for use on DSLR cameras, and are no substitute for an f/1.4 or f/1.2 lens that was designed for your camera. However, they easily can produce very distinctive images. Here's how to use one on a DSLR....
 
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Step 1Get a Lens

Get a Lens
Start by getting one of these ultra-fast lenses.

The example here is a Kowa 1:1 55mm, an f/1.0. There are lots of others to choose from, mostly branded Kowa or Rodenstock. The Kowa shown here cost $25, including shipping, via eBay. Personally, I've purchased ultra-fast lenses from two eBay suppliers: ctr_surplus and svcompucycle.

Fundamentally, these are commonly junked lenses and should not be too expensive. However, these lenses were used in very expensive equipment and probably cost a lot when new, and people often go nuts when they see fast apertures, so pricing varies wildly. The Kowa 1:1 55mm is among the cheapest and most commonly available, but there are many alternatives. I've heard that one can find ultra-fast lenses for $1 in junk yards if you're diligent and dress like a buck is all you can afford. However, surplus stores and eBay sellers are commonly listing ultra-fast lenses anywhere from $10 to $400. Some of the more exotic ones, or ones with DSLR-compatible mounts, are between $600 and $2,000.

In any case, you want a lens with a rear element that fits inside the diameter of your DSLR's mount. A lens with a larger rear element generally might imply vignetting, as well as being harder to mount on your DSLR. Independent of the rear element diameter, large diameter lens barrels can complicate mounting by colliding with an overhanging finder or a front hand grip on your camera body.
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6 comments
Oct 20, 2011. 10:03 AMavatar_i says:
Oh- that is so VERY COOL!

I have several OLD barrel lenses [large format, 360~500mm] I have acquired over the years, and one was mounted on a long aluminum pipe with a camera mount on it, probably made it about */- 800mm focal langth [?].
Not too stable, though.

Always wanted to put it on my Nikon D700, but couldn't figure out...
Thanks!
Nov 13, 2010. 8:10 AMelectronbee says:
Whoops, sorry about that ProfHankD! I just read the intro and went straight to looking at your pictures!
Nov 12, 2010. 8:45 PMelectronbee says:
Actually, the stated f/ will only be at the designed specifications of the lens itself. A lot of these lenses have an extremely short back focal length. So, if your camera has a lens-mount to sensor distance of say 43mm and your lens has a back focal length of 15mm then the projected image will be larger than designed and the amount of light hitting anyone area will be reduced. Similar to a macro lens will have you have to increase exposure the higher your magnification.

The lenses will still be fast, especially for the money, but not as fast as one thinks.
Aug 30, 2010. 8:41 PMnukemall says:
Good work!

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Author:ProfHankD(Prof. Hank Dietz)
I'm an Electrical and Computer Engineering Professor at the University of Kentucky. I'm probably best known for things I've done involving Linux PC cluster supercomputing; I built the world's first b...
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