Why aren't there more f/1.0 lenses?

[biochemiker]

I am wondering why there aren't more fast wide angle lenses. It would seem like an f/1.0 lens would be fairly easy to make as the aperture of lenses 50mm and smaller would be the same as the focal length.

There must be an obvious reason why this is difficult because the market isn't flooded with 18mm f/1.0 lenses! (Or even sub f/1.0 lenses like the "famous" 50mm f/0.95 that I've heard about.)

 

[Greg Fiske]

My guess is that the quality of the glass has to be superior because the more light it can handle the more the imperfections show up. Things like micro bubbles and green tint. But I have no idea, so hopefully someone with more experience will chime in.

 

[calvinboy24]

Quite the opposite. I think it is very difficult to make lenses that fast. Tolerances and precision of the glass is needed for focusing, good edge performance, and sharpness wide open.

These lenses are incredibly expensive for a reason. And at these prices, there aren't a lot of potential customers either.

I am wondering why there aren't more fast wide angle lenses. It would seem like an f/1.0 lens would be fairly easy to make as the aperture of lenses 50mm and smaller would be the same as the focal length.

There must be an obvious reason why this is difficult because the market isn't flooded with 18mm f/1.0 lenses! (Or even sub f/1.0 lenses like the "famous" 50mm f/0.95 that I've heard about.)

 

[camera_nut]

The problem is getting all the light to converge properly onto a flat image plane (the sensor)

If they come up with a way to make a semi-spherical sensor (like your eye) the problem becomes much easier. But I don't think you can do zooms that way. The curvature has to match the focal length. It's always something.
--
Vince

 

[tkbslc]

Cost vs benefit + IQ compromises.

The lenses end up being not as good optically as say a good f1.4, but they cost 10-20x more money. It's a LONG way from f1.4 to f1.0 and a lot of compromises and/or expenses have to made to get there.

 

[One DaveT]

A f1.0 lens has twice the surface area as a f1.4 lens. There is twice glass that must be formed without imperfections, and twice the surface area that must be ground perfect without imperfections. I highly doubt that it's a linear function of size to number of imperfections..... probably more likely logarithmic. This translates to cost.

And what's the benefit? Might shave a few more mm of the DOF? Though DOF is a function of aperture, focal length and shooting distance, so there is a cost comparison to just going with a longer focal length.

With regards to low light shooting, it also competes with other focal length trade offs. A 24/1.4 has the same hand-hold-ability as a 50/1.0. When one starts maxing ISO, and aperture widths at the focal lengths, personally, I can't see well enough to even manual focus, let alone camera AF.

 

[tokengirl]

Cost vs benefit + IQ compromises.

This would be my guess, combined with a probable lack of demand. Look at what an 18mm lens is typically used for: landscape and architecture. Is a f1.0 lens really needed for this type of work?

 

[Lee Jay]

...and dispersion is too high. Well, that's the fundamental reason, anyway. These make the lenses large, heavy and complex to compensate for aberrations.

--
Lee Jay
(see profile for equipment)

 

[slydog]

Why do you want an F/1.0 lens?

Have you ever played around with a DOF calculator?

Have you ever held an 85L 1.2 in your hand? (or checked the price)

If you answer yes to any of the last 2 questions, then I would ask you the first question again.

 

[biochemiker]

My question is more theoretical since I don't particularly need a lens that fast. I am more interested in the physics.

I know the math behind f/numbers and all that. You know that if Canon made an f/1.0 28mm or 35mm lens, there would be people that buy it regardless of how heavy it is.

The math says that the entrance pupil should be 35mm in a 35 mm lens for f/1.0. This is compared to 5 cm for the 50mm lens which exists.

So, one would think that a 35mm or 28mm f/1.0 would be smaller than the 50mm f/1.0 and much smaller than the 85mm f/1.2. This would not seem to be an insurmountable problem.

ltfinger's comments make the most sense about why it is difficult to make lenses of these focal lengths that fast.

 

[Lee Jay]

So, one would think that a 35mm or 28mm f/1.0 would be smaller than the 50mm f/1.0 and much smaller than the 85mm f/1.2. This would not seem to be an insurmountable problem.

ltfinger's comments make the most sense about why it is difficult to make lenses of these focal lengths that fast.

Because they have to be retrofocus.

http://en.wikipedia.org/wiki/Retrofocus

If it weren't for that, they'd be smaller just like your intuition tells you. The registration distance on the Canon EF mount is 44mm, so any lenses shorter than that have to be retrofocus.

--
Lee Jay
(see profile for equipment)

 

[camera_nut]

You left something out.

Because of the mirror being in the way these need to be retrofocus lenses which are far more difficult and require a larger objective size. If you ever looked inside a rangefinder (or point n shoot) you'd see the rear element of the lens nearly touching the film (or sensor)

Compare the size of a 50mm f1.4 lens for a Leica with same for an SLR. The rangefinder lens is way smaller.

Also, as you said "I don't really need one" That's the biggest reason they don't make it.
--
Vince

 

[Lee Jay]

Compare the size of a 50mm f1.4 lens for a Leica with same for an SLR. The rangefinder lens is way smaller.

The 50/1.4 isn't retrofocus.

--
Lee Jay
(see profile for equipment)

 

[biochemiker]

Now I have a complete answer. Index of refraction and retrofocus.

Retrofocus isn't quite as intuitive as index of refraction, but I think I got it. To make an image circle of the correct size at the right distance, the lens elements of a retrofocus lens are basically from a longer focal length lens. The retrofocus element is at the front of the lens and gathers a wider angle field of view than the "native" focal length of the lens allowing both a wide field of view and a larger distance between the sensor and the back of the lens. Is this sort of correct?

 

[Lee Jay]

Now I have a complete answer. Index of refraction and retrofocus.

Retrofocus isn't quite as intuitive as index of refraction, but I think I got it. To make an image circle of the correct size at the right distance, the lens elements of a retrofocus lens are basically from a longer focal length lens. The retrofocus element is at the front of the lens and gathers a wider angle field of view than the "native" focal length of the lens allowing both a wide field of view and a larger distance between the sensor and the back of the lens. Is this sort of correct?

Sort of. I like to think of a wide retrofocus as an ultrawide with a backwards telephoto at the back. An ultrawide retrofocus is an ultra-ultra-wide with a backwards telephoto at the back.

--
Lee Jay
(see profile for equipment)

 

[camera_nut]

Maybe not technically.... but the non SLR lenses have rear elements much closer to the film/sensor. So my point is just that the mirror makes things difficult.
--
Vince

 

[Badbatz]

There must be an obvious reason why this is difficult because the market isn't flooded with 18mm f/1.0 lenses!

Yes, several. Cost (how about 20 000 - 50 000 dollars); quality (even for $20K you'd get lots of aberrations and distortions that maybe another $30K would cure, maybe not...); size/weight (peanuts, maybe just 4-5 pounds.) You get the drift, lens like this is not economically feasible if possible at all.

 

[biochemiker]

The Canon EF 50mm f/1.0L was purchased used for $2,672.22 on average according to fredmiranda.com. Are you sure that the price for a shorter focal length would be 10 times that? Besides, whatever the cost, someone would be willing to pay it. People by the 800mm f/5.6L and leased the 1200mm f/5.6L.

Still, I was more interested in the technical aspects than the practical aspects such as size, weight, and price.

 

[Lee Jay]

Maybe not technically.... but the non SLR lenses have rear elements much closer to the film/sensor. So my point is just that the mirror makes things difficult.

On 50mm lenses, the rangefinder folks shouldn't put the rear element that close to the sensor. It doesn't help anything.
--
Lee Jay
(see profile for equipment)

 

[One DaveT]

ltfinger's comments make the most sense about why it is difficult to make lenses of these focal lengths that fast.

Not to take any credit from Lee, but I would speculate that you only say that because you have given less consideration to the answers, than the amount of thought or experience that has gone into the answers. There are many good replies here, all with valid and relevent points. I