A "fast" lens

[Edalongthepacific]

What is a fast lens? I would say any lens between f/1.2 and f/2.8. Agree?

[scooby70]

But why rule out anything "faster" than f1.2?

How about... faster = faster than f2.8?

[Edalongthepacific]

Well, I guess I was thinking that for all practical purposes an f/1 lens was unavailable. Can an f/1 lens be made and priced within reasonable limits? I have heard that there are lenses faster than f/1 but how can that be?

[Sareesh Sudhakaran]

I think the fastest lens ever is the Zeiss 50mm f/0.70, used for Barry Lyndon by Stanley Kubrick.

[Jim Pascoe]

Well, I guess I was thinking that for all practical purposes an f/1 lens was unavailable. Can an f/1 lens be made and priced within reasonable limits? I have heard that there are lenses faster than f/1 but how can that be?

Well I have a Voightlander 25mm f0.95 and it is currently available in Micro 43 mount.  Great lens - you will find a review of it somewhere on LL.  They have also just released a 17mm lens also f0.95.  (these are equivalent to 50mm and 35mm in full frame).

Jim

[mediumcool]

I think the fastest lens ever is the Zeiss 50mm f/0.70, used for Barry Lyndon by Stanley Kubrick.

… and for shots of the dark side of the moon. Cue Pink Floyd. 

[ErikKaffehr]

Hi,

F-stop is aperture divided by focal length. Increasing the opening of the lens so it is larger than the focal length will make for F-stop < 1.

I'm not sure there is a theoretical limit, although it may do with total reflection at certain angles, but that would only occour on glass air surfaces, I think.

Best regards
Erik

Well, I guess I was thinking that for all practical purposes an f/1 lens was unavailable. Can an f/1 lens be made and priced within reasonable limits? I have heard that there are lenses faster than f/1 but how can that be?