Better 10-22mm lens for Canon

Question

The famous Canon 10-22mm lens is quite well-built. The image is sharp near the corners, and it has a fast auto-focus system.

But unfortunately, it's aperture is relatively narrow...

Would there be any very wide angle lens of comparable focal characteristics, that would have a significantly larger aperture, and that would be adaptable on Canon cameras ?

Asked by Skippy Fastol

Answer

Quality of the Tokina 11-16mm F/2.8 is amazing. There is one for Canon mount. You lose some on the long end but if you already have some that starts around 17mm it should be good. Otherwise maybe you look at prime lens but I have trouble finding wide and bright ones for cropped sensor. I looked too :)

Answered by Zak

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In what kind of scenes does it make sense to use f/1.4 aperture?

Question

I have been told that it is difficult to focus with an aperture of f/1.4.

So, in which kind of scenes does it actually make sense to use the f/1.4?

In portraits they say that it is important to keep focus on both eyes (ruling off f/1.4).
In moving subjects (street photography) it s simply not possible to focus with f/1.4.
In food photos it will then focus only a particle of food.

What are the PRACTICAL uses of f/1.4?

Asked by Anisha Kaul

Answer

There's several practical cases here. Your depth of field isn't only a function of the aperture so if other factors suite, then its still fine.

If you're sufficiently far away from your subject, then using f/1.4 would result the majority of your subject being in focus.

If you have a high performance AF system (something like the 7D perhaps), then you're more likely to keep the point of focus exactly where you expect.

If the scene is so dark, you may need to shoot at a wide open 1.4 in order to get enough light - you're willing to trade extreme subject isolation and possibly not get the exact point of focus for noise and proper exposure.

You do see it in portraits some. Its a very trendy thing to do to. The eyes should be roughly on the same focal plane, so you should be able to get them in focus and the ears will be blurred out.

Frankly though, I don't - nor do most people I know - use f/1.4 all that often.

Answered by rfusca

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Is overall light gathering of a lens only dependant on aperture?

Question

My impression is that the aperture value of a lens determines its light gathering ability, but I'm not sure I understand how it works...

When considering light gathering in telescopes, it is dependant on the diameter of the objective lens (or mirror). This makes perfect sense to me, since light is radiated in all directions, so a larger area means you gather more light. It seems to me it should be the same in camera lenses also - a larger lens would pick up more of the cone of light from the subject, and focus it onto the sensor.

What got me thinking about it was I've seen an F/0.95 lens, but it doesn't look hugely larger than F/2.8 lenses, so I don't understand the physics of how that would work.

Answer

Essentially yes, light gathering ability of a lens is determined by its maximum aperture. Transmission rates of the materials used also has an effect but it is very small.

You intuition is correct in that you would expect a large aperture lens to have a large barrel, however the aperture is specified as a ratio of the apparent* size of lens opening divided by the focal length. So a 200mm f/2.0 lens must have a front element large enough to see a 200/2.0 = 100mm aperture, so the barrel must be at least 10cm. However a 20mm f/2.0 only appears to have a 10mm aperture, which is small is comparison to most lens sizes.

To complicate matters wide angle lenses need larger front elements than dictated by their aperture to prevent vignetting across the frame. For focal lengths shorter than about 50mm lens sizes increase as focal length decreases despite apertures, and thus light gathering ability, also decreasing.

Here's nice example, this Nikon lens is only f/2.8:

but is absolutely huge, due to its extreme wide angle nature.

* note that 100mm f/2.0 doesn't mean the physical opening in the middle of the lens is actually 50mm diameter, only that the image of said opening when viewed through the front of the lens appears to be 50mm in diameter. The actually opening is often smaller, but the lens front element has to be large enough to accommodate its theoretical size.

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