What does the aperture range mean?

yoyostock

Can someone explain what the aperture range on a lens means? For example, Canon's 17-85mm lens indicates a designation of f/4 -5.6. What does that f/4-5.6 range mean? I know I can shoot f/5.6, f/8, etc. and beyond and I believe I cannot shoot any faster than f/4, with that lens. So why not just indicate it as f/4? What's the f/5.6 part supposed to indicate?

To compare, Canon's 50mm f/1.8 doesn't have a range. I can shoot f/1.8 on up. Is it because it's a prime lens?

But then again, the Canon's 17-55mm f/2.8 doesn't have a range either, although it's a zoom.

Eh? :dunno

Scott_Quier

As you zoom the lens, the maximum aperture available changes. It's a function of the size of the lens objective element and the focal length and the amount of light transmitted to the sensor.

So, for the aperture range example provided (I'm assuming you copied it correctly ), at 17mm, the maximum aperture if f/4. At 85mm, it's f/5.6. This is the maximum aperture available. You are free to use any smaller (larger f-stop number) that you please, up to the minimum aperture available.

claudermilk

To complete the explanation, the 17-55/2.8 does not have a varaible maximum aperture, so you can be at f2.8 throughout the zoom range from 17mm to 55mm. That's part of why it's more expensive.

yoyostock

Scott_Quier wrote:

As you zoom the lens, the maximum aperture available changes. It's a function of the size of the lens objective element and the focal length and the amount of light transmitted to the sensor.

So, for the aperture range example provided (I'm assuming you copied it correctly ), at 17mm, the maximum aperture if f/4. At 85mm, it's f/5.6. This is the maximum aperture available. You are free to use any smaller (larger f-stop number) that you please, up to the minimum aperture available.

Ahhhaa...got it. I thought that the range probably had something to do with the zoom aspect, but the 17-55 threw me off. If it zoomed any further out, I suppose it too would have a range.

Scott, per your recommendation, I ordered a new battery and charger from Sterlingtek. So far so good...

Thanks!!!

Scott_Quier

claudermilk wrote:

To complete the explanation, the 17-55/2.8 does not have a varaible maximum aperture, so you can be at f2.8 throughout the zoom range from 17mm to 55mm. That's part of why it's more expensive.

Good point that I missed!

TylerW

Here's a related question: Why aren't there any zoom lenses (that I've heard of, at least) that are faster than f/2.8? Is it a technical limitation of zooms that primes are able to overcome?

pathfinder

Tyler,

I am not sure if the limiting factor is that the lens manufacturer's cannot build a zoom faster than f2.8 or not.

But I am sure that they cannot build zooms faster than f2.8 ( say f 1.4 ) at a price point the public will pay.

For instance a consumer 70-300f5.6-f6.3 zoom may sell for around $600, but a 300 f2.8 sells for $3,000. If it were a 70-300 f1.8, it would cost much, much more than the 300f2.8 prime. The market for lenses costing >$5,000 is very, very thin.

I think that there are serious optical reasons that zooms are not built faster than f2.8 also. Look at the size of the front elements on a 200 f1.8 lens ( yes, Canon built one and Nikon still makes a 200f2 I believe) or even a 400mm f2.8

ziggy53

TylerW wrote:

Here's a related question: Why aren't there any zoom lenses (that I've heard of, at least) that are faster than f/2.8? Is it a technical limitation of zooms that primes are able to overcome?

Olympus has a couple:

35-100mm f/2.0 ED Zuiko
14-35mm f2.0 ED Zuiko

The main problem in either full frame 35mm or crop 1.5/1.6 is that an f2.0 zoom would be extremely large, extremely heavy, and "Extremely" expensive.

If you look at the superfast primes you can get a feel for some of the problem. The Canon 200mm, f1.8L is a "prime" example. (nYuck, nyuck)

For each increase in f stop you have to increase the light gathering by a factor of two, and not just the front element. This also requires more substantal support and larger tubes.

Now factor in the reduced scale of production and still having to recover development costs.

Most manufacturers just don't see a market.

Olympus is a bit different in that their whole digital system is scaled down with the reduced sensor size. Still, the Olympus super fast zoom lenses are "very" expensive and I'm sure not too many copies exist in the world.