That's *range* of apertures. Set them to the same aperture, and same is what you get with the exception that the lens is normally wide-open before the actual exposure, so AF and viewing is through that...
The aperature listed is the maximum it can open. f/8 is the same on both lenses. The only difference (minus others in image quality, build, MTF, etc etc) is that one opens to f/1.4 and the other to f/1.8.
If you see a range, such as f/3.5-5.6, that usually means the lens is maximum f/3.5 at the short end, and maximum f/5.6 at the long end..
As a n00b trying to get my head around aperture....
For two given lenses of the same focal length, say 50mm f1.8 and 50mmf1.4, is the 1.4 consistently 2/3rds of a stop larger aperture acrossthe aperture range?.
That is, if they are both stopped down to f4, is the 1.4 still 2/3rdslarger?.
That would make sense, if I understand things correctly..
If you see a range, such as f/3.5-5.6, that usually means the lens ismaximum f/3.5 at the short end, and maximum f/5.6 at the long end..
To clarify, if you see a range of aperture on a zoom lens theatrus is correct..
Comparing two 50mm fixed focal length lenses, say a 50mm f/1.4 and a f/1.8 they will both take roughly equivalent shots at f/4. Obviously the f/1.4 can use that aperture and f/1.8 cannot. Both will be able to take a shot at f/1.8. The differences in look between the two lenses at the same aperture will be elsewhere... color, contrast, out of focus rendering. These differences may be important or may not be important to you for your purposes.
The more expensive lens sometimes, but not always has better build quality..
If your question is, I'm either going to buy a 50mm f/1.4 or f/1.8, which one should I get? The answer is probably get the cheaper f/1.8. I don't think any major brand makes a prime 50mm dog of a lens. The f/1.4's have their value over the 1.8's, the difference will likely show up only under heavy daily use...
I had assumed the physical size of the aperture was the same in both lenses, which is why the minimum f-stop on the 1.4 is 16, and the 1.8 is 22. (with the Nikons anyway)..
I'm now left wondering why the 1.4 doesn't stop down to f22 :Cheers!..
Worry more about the build quality and the number of blades in the aperture iris. All other things equal (which they never are) an aperture iris with 5 blades will not render out of focus areas as well as one with 9 blades. You are now getting into the range of diminishing returns that not everyone cares to pay for. You will pay for diminishing returns to a significant degree. This is subjective and no one but you can answer if it's worth the value. If you ask which one is better in an absolute sense, cost no object, the more expensive lens with 9 blades is probably better..
With respect to f/16 or f/22 I'd call it a different optical design and not worry about it unless you have a very specific reason to notice the difference. Both settings are outside of the optimum performance of either lens...
I attempted to give you a practical concept of aperture..
Here's a more technical description if this is what you're after:http://en.wikipedia.org/wiki/Lens_aperture..