Theoretical Maximum Apeture...

[Apemaster]

Hi all. I've been browsing for a while, but I thought I'd show my face now...

Just out of interest... What is the maximum aperture possible for a (EF mount) lens? Limited only by the size of the EF mount, what would be the largest possible value?

I'm not actually what the apeture value actually means. Does it equate to the size in mm in any way? What happens when you get below f/1? presuming you can...

might be interesting, is all... ;)

[Doom1701e]

Thats a tough one to explain, i'll leave it up to one of my fellow forum members. I just thought I would say welcome to the forum!

[ZuluCB]

You'll find this interesting: http://en.wikipedia.org/wiki/F-number

[sapearl]

Well, I don't know about an EF mount lens, but about 25 - 30 years ago if not longer, there was an f0.95 lens for the Canon 7 Rangefinder I believe.

[ZuluCB]

"If you do decide you want the fastest possible lenses, go buy yourself a Leica M6 or M7, for which you can buy a 50mm f/1.0 lens and a 75mm f/1.4. And before you think that it's modern technology that allows these wonders, recall that Canon made a 50mm f/0.95 for their rangefinder cameras back in the 1950s."

http://www.uscoles.com/fstop.htm

[Apemaster]

Cheers for the link, it answered my next question, "what is the f-number of the human eye?". (8.3-2.1, in case you don't want to read it...):)

[CyberDyneSystems]

I've seen faster than f/0.95 lenses made fro non camera related use... projectors, and prehaps enlargers. People have converted many of these to work on the EF mount (totally manual of course) as well. the results are usually.. less than appealing :lol:

[cjm]

What would happen? Probably toooooooooooooooo much blur. Probably total blur.

[Atomic79]

For you historians a little off topic (not an EF mount lens) but I believe this is still true:

The Zeiss 50mm f/0.7. The fastest lens of all time. 3 were built for NASA during Apollo, of which Stanley Kubrick got a hold of two for which he had custom mounts built for some cine camera (I'm guessing a Mitchell). Used them to film a candle light scene in "Barry Lyndon"

[pfogle]

The max aperture possible is determined by the size of the lens mount. Assuming the flange is about 50mm from the sensor, and it's roughly 50mm in diameter, that would equate to an f1.0 lens - which Canon do make. I doubt you could get much bigger than that.

[Coco-Puffs]

I saw that f0.95 lens in Tokyo the other day...and 'wow' was all I can say. Then I looked down and looked at my nifty...[rolls eye]

[CoolToolGuy]

The max aperture possible is determined by the size of the lens mount. Assuming the flange is about 50mm from the sensor, and it's roughly 50mm in diameter, that would equate to an f1.0 lens - which Canon do make. I doubt you could get much bigger than that.

That would be true for a 50mm lens. However, a 25mm lens made to maximize that configuration could theoretically be an f0.5. I don't think any manufacturer has actually built anything like that, though.

Have Fun,

[RuggerJoe]

Remeber the appeaature is bassed on a single element design. The actually apperature being somewhere inside the set of lenses is probably actually smaller than 50mm on a 50mm f/1.0 lens.

[coreypolis]

Leicas 50 f/1 noctilux

http://img.photobucket.com/albums/v721/viperx27/56196343.jpg

(taken with a 200 f/1.8 at 1.8 :))
it was way heavier than expected, though smaller overall

[ron chappel]

I should point out that the mount size has not alot to do with the maximum aperture!
This seems to be a myth that won't die.Other versions are that nikon can't possibly offer an f1.0 lens because their mount is too small,etc,etc
Just look at the canon 7 or leica rangefinders with their relatively small mounts.The register distance is not a real issue either as far as i can see.Surely that is dead easy to work around with a reverse retrofocus design?

Anyway-onto more interesting stuff-
Atomic is right about the f0.7 lens used by Kubrick.If you look around the web you can easily find a few webpages about it all.
While searching i found the baker 'super schmidt' lens.This one is a 16 inch focal length f0.5 schmidt mirror lens used for tracking meteors

So - what is the ultimate limit for f stop?
I do remember reading it once but have forgotten the exact number.It all has to do with the limit imposed by the light having to travel through air which makes the limit f0.5 (if the stuff i'm reading on the net right now is correct.It's a difficult thing to search for)
To go under that limit one has to imerse the subject in oil as some microscopes do.

[Krapo]

What about Hubble? :)

[Andy_T]

The Zeiss 50mm f/0.7. The fastest lens of all time. 3 were built for NASA during Apollo, of which Stanley Kubrick got a hold of two for which he had custom mounts built for some cine camera (I'm guessing a Mitchell). Used them to film a candle light scene in "Barry Lyndon"

Found more on the conversion of this lens here:
Two Special Lenses for "Barry Lyndon" by Ed DiGiulio (President, Cinema Products Corp.)

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

Best regards,
Andy

[tiziano]

Found more on the conversion of this lens here:
Two Special Lenses for "Barry Lyndon" by Ed DiGiulio (President, Cinema Products Corp.)
(http://www.visual-memory.co.uk/sk/ac/len/page1.htm)Best regards,
Andy

Thanks Andy. This was very interesting.

[My Porsche]

ccould there be a negative f-stop? like the aperture is bigger than the end of the lens? there's just a seperate bigger part of the lens that hols that?

[DocFrankenstein]

You can build anything you want. I can put an converging lens with f=50mm, 100mm diameter and get myself a whopping f/0.5 lens.

But who needs that?

Judging solely on the angle, the EF mount is going to start cutting off the rays coming onto the film at smaller than 45 degrees. So unless you're into building a retrofocus superfast lens, the max aperture should be around f/1 for lenses of normal and longer.

[DocFrankenstein]

ccould there be a negative f-stop? like the aperture is bigger than the end of the lens? there's just a seperate bigger part of the lens that hols that?
No, because it's a ratio. You can't divide two positive numbers to get a negative.

It can get dangerously close to zero though. ;)

[tiziano]

Being a ratio between two lenghts, and therefore between two positive numbers, it cannot be negative.

[tiziano]

Doc... you beat me... :)

[sapearl]

Beautiful piece of hardware Corey. A long time ago when I was back in school our photography class had the pleasure of "borrowing" a Leica collection for a day. We got to pick our hardware. I selected the M4 with the 90mm 2.0, I believe it was. Not as nice as your noctilux, but pretty darn cool to a college kid ;) . - Stu

Leicas 50 f/1 noctilux



(taken with a 200 f/1.8 at 1.8 :))
it was way heavier than expected, though smaller overall

[rdenney]

The f-stop is the focal length divided by the front aperture, not the diaphragm. The two are the same only for telescopes and other optics designed for full-aperture use. Even telescopes routinely have baffles at much smaller diameters than the front aperture.

I have a 180mm f/2.8 Sonnar that should have a maximum aperture diameter of 64mm, but it is easily adapted to the Canon. The front element is indeed at least that wide, though it may be further constrained back where the aperture blades are. Those are located according to the optical and mechanical design. All the light in the lens passes through a single point somewhere along the path.

So the maximum speed allowed by a lens mount is quite a difficult thing to nail down. The Canon Serenar 0.95 was used on the old Canon rangefinder that had a 39mm Leica thread mount. The EF mount is larger and farther from the film.

I think it would be quite possible to have a 50mm f/0.5 lens through the EF mount, if it is possible to design the lens at all. The front element would be 100mm in diameter and the barrel would have to accommodate that wide path. You might run into problems with the ideal location of the aperture and the mount, but it's not at all obvious how to know those limitations outside the context of a particular design.

Of course, designing glass that would perform adequately at such speeds would be nearly impossible. There are just too many conflicting trade-offs. But lenses under f/1.0 are quite common for use in security surveillance cameras, etc. But for them the optics need be no better than what is required by video.

Someone said that even air precludes speeds faster than f/0.5. That's not quite correct. The fastest possible t-value might be 0.5, but f-stops are defined by the size of the front aperture, not by the actual transmission of light. But you run into the limitations on the ability of the glass to refract to get such a large front element to turn the light into the optical center of the lens. It would take extreme shapes, and that would cause truly monstrous chromatic aberration, etc.

Rick "who thinks even the Noctilux has performance limitations" Denney

[pfogle]

Rick, I know I should go get the book, but IIRC, the aperture can be either the distance from the focal plane to the front nodal point divided by the front aperture as it appears looking into the front of the lens (as distinct from the size of the front element).

Equally, I think it can be got from the distance from the focal plane to the rear nodal point divided by the rear aperture, as seen from the back of the lens.

Lots of lenses for SLRs have the rear node about 50mm from the focal plane, to clear the mirror, so the f1.0 lens will have it's rear node roughly at the rear element, giving the figures I used.

To get to f0.5, the 50mm rear element would have to be 25mm from the sensor - possible with a rangefinder, maybe, but not possible in an SLR.

Like I said, it's a long time since I studied this stuff, so apologies if I've got it wrong.

[Jon]

Tperture used in aperture calculations is actually the "entry pupil", the apparent light-gathering area for a lens.This is influenced by the front element and the diaphragm. For an example of how this works, look at any constant-aperture zoom. As you zoom, the front element remains constant in size but the front group magnifies, and therefore changes the apparent diameter of, the diaphragm to varying amounts as viewed from the front. The diameter of a lens mount could constrain the exit pupil, but this doesn't constrain the light-gathering ability of the lens at all.

Wall & Jordan, Photographic Facts and Formulas suggests this simple test to demonstrate the aperture: place a point light source at the focal point of a lens focussed at infinity (find a film body, lock the shutter open, and place a pinhole light source in the shutter opening, would be one method), and measure the diameter of the light beam that emerges from the lens.

[rdenney]

Rick, I know I should go get the book, but IIRC, the aperture can be either the distance from the focal plane to the front nodal point divided by the front aperture as it appears looking into the front of the lens (as distinct from the size of the front element).

Equally, I think it can be got from the distance from the focal plane to the rear nodal point divided by the rear aperture, as seen from the back of the lens.

Lots of lenses for SLRs have the rear node about 50mm from the focal plane, to clear the mirror, so the f1.0 lens will have it's rear node roughly at the rear element, giving the figures I used.

To get to f0.5, the 50mm rear element would have to be 25mm from the sensor - possible with a rangefinder, maybe, but not possible in an SLR.

Like I said, it's a long time since I studied this stuff, so apologies if I've got it wrong.

No expert me.

But what if there are no lenses behind the aperture or the rear nodal point? After all, a telescope has only the primary objective and the front and no lenses at all behind the nodal point. Thus, I can conceive of a simple lens with a 3" focal length and a 6" diameter of the primary objective that would fit in front of even an SLR. As long as the mount doesn't occlude the rays coming through the edge of the objective, it would work (a big if, I realize). I seem to recall that for a simple lens, the rays cross halfway between the lens and the focal plane, which is about where the mount would be. The performance would, of course, be dreadful with such a simple lens.

My main point (which you demonstrate and probably agree with) was that the relationship between apparent aperture and the dimensions of the barrel and lens mount are in no way obvious, and I doubt that the EF mount is as significant a deterrent to faster designs as the other issues that make fast lenses difficult. For one thing, modern autofocus technology may not have the precision needed to focus a lens where the depth of field is a fraction of a millimeter and where being only slightly out of focus results in unacceptable blur. And controlling aberrations at extremely fast f-stops would be quite a challenge when the standard is a 12-megapixel sensor or a piece of film. There are lots of reasons why lenses don't get faster, but I don't the mount is the most significant of them.

Rick "who thinks smaller sensors will make faster lenses possible in cameras purpose-designed for small sensors, but will have other limitations" Denney