quick question :)

hammerhead_05 · Sep 13, 2007

I am interested in upgrading from a Finepix S9000, and I am searching everywhere. One thing I would like is to have a camera that has a lense to be able to keep the widest aperature, even when at maximum focal length - quite expensive, I see.

But I also came across cameras with small lenses, and the specs on it was "1:3.5-5.6" . :raisedbrow: What does this mean? Does this mean that the lense ONLY opens from 3.5-5.6? Is that it? Or am I missing something? And also, what is the 1 for ?

Hopefully someone knows the answer to my questions. :mrgreen: Thanx for all your help in advance!!!

Garbz · Sep 14, 2007

No only the widest aperture is specified on the lens. The stopped down value is always the same over the range.

What that means is that when zoomed out the widest aperture is 3.5, when zoomed in it is 5.6. Making a lens that has a fixed aperture over the zoom is expensive which is why you pay quite a bit more for a 1:2.8 on a zoom lens.

Big Mike · Sep 14, 2007

That's correct, when you see a range of F numbers in the name of a lens...it's the range of the maximum aperture...which changes as the lens is zoomed out. But you can always stop the lens down to a smaller aperture. Most SLR lenses can go down to F22 or smaller. Digicams may be more limited.

The '1' is there because the F number is actually a ratio. F4 is actually 1:4 or 1/4. It's a ratio between the diameter of the aperture opening and the focal length. So when there is a range, the actual opening isn't getting any smaller, but the focal length is changing...so therefore the ratio changes and the F number changes.

When you see a zoom lens with a 'constant' maximum aperture...like 24-70 F2.8...the aperture opening actually gets larger when you zoom out...so that it can maintain the 1:2.8 ratio.