Kubrick's Zeiss 50/0.7 lens

RA40 · 02-09-07, 10:54 AM

http://www.visual-memory.co.uk/sk/ac/len/page1.htm

Nice write-up, just wish the pics were better.

Some years back I met a filmaker who would buy various MF still lenses and have them modded for his film cameras. Fascinating accounts what can be done given the $$ and skilled technicians.

Percy · 02-09-07, 12:49 PM

Neat writeup, but the pics of the lens might be also distorted. The front element of a 50mm 0.7 lens should have a front diameter of 72mm - this is for the front of the lens itself. The picture, assuming that the focal plane is behind the barrel housing, would suggest otherwise. With the adapters and modifications, it would appear that the lens is shooting at about f/1.5 or so.

A focal ratio of 1.0 or faster (.9, .8, etc) would have the front element being larger than the distance to the focal plane...in other words, very short barrel, very large lens. The lens diameter would be larger than the barrel dimension. Lens would be 72mm in diameter, barrel should only be 50mm in length AT MOST. It doesn't look like that in the picture.

The other lens being shown, the 36.5mm, has what is called a Focal Reducer attached. In this case, about a .75x ratio. Commonly used in astronomy purposes. IF they kept true to the focal ratio (kinda skeptical), the 36.5mm would have a focal ratio of f/0.5!

It would be interesting to shoot a starfield to see how well or poorly corrected these lenses are. Tenmon guide did a recent test on some of the rangefinder lenses as well as video lenses and they didn't perform too well at all wide open. Most needed to be stopped down to f/5.6 before they were acceptable.

Interesting writeup though!

Percy

jmaynard · 02-09-07, 01:05 PM

Quote:

Originally Posted by Percy

A focal ratio of 1.0 or faster (.9, .8, etc) would have the front element being larger than the distance to the focal plane...in other words, very short barrel, very large lens.

The focal length is independent of physical lens size. If it weren't, a 50/1.2 would be just as long as a 50/1.8, and I've never seen one that was. in addition, retrofocus designs (which are quite commonly used for 35mm SLR wideangles) are inverted telephoto designs, which also wind up being longer than the focal length would suggest.

Percy · 02-09-07, 03:28 PM

There's only one real way to solve this...let's get that lens and put it on the optical test bench!

I'd hate to see the CA on that lens though. It's bad enough on a 50 1.0L wide open. Same with the Canon f/0.95 lens. You can only bend light so much before it does nasty things, even with ED/SD/UD/Fluorite in the optical formula.

Magic sweet spot for a 92mm diameter lens...around f/4.9 for exceptional color correction to 500x. Larger the diameter, the more the focal ratio has to be, even with the highest grade glass and other materials available today. (Refractor/lens based...not mirror based).

Percy