Lens Speed

[Rina Minca]

Question for everyone out there:
I am very new to SLR photography and I am just figuring out the lingo. I've gotten most of it down pat, but I am so confused about lens speed. What is it and how do I use the knowledge to my advantage? Is it different for different focal lengths or does it depend on the particulars of the lens you get? If these questions don't even make sense, then it just shows how much I am in the dark.
Thank you in advance.

[BCampbell]

I guess you're talking about when people say a lens is "fast".

This just means that it has a wide maximum aperture, usually f/2 or wider.

This is called "fast" because by letting in more light, you're able to get faster shutter speeds, especially in low-light situations. When looking at a lens description, the f-number you see is the widest possible aperture.

Some zoom lenses will have a range. For example, "70-300mm f/4-5.6. This means that f/4 is the widest aperture at the shortest focal lengths (70mm in this case) and f/5.6 is the wiest at the longest length (300mm). Other zooms have a fixed maximum aperture, and will just say, for example, "17-50mm f/2.8". Generally, a zoom with a fixed maximum aperture is a higher quality lens.

[Raoul Isidro]

I used to think the word fast in a lens was the speed of money draining from your wallet. The faster the lens, the faster the money drained. I guess, in a way, it still applies today, but I'm sure the rest of the people in this forum will explain it heaps better than this...

[inkista]

All the Canon and Nikon zooms max out, btw, at f/2.8. Olympus has a few zooms that max out at f/2.

f/2.8 is the borderline maximum aperture you need to do "available light" photography, which for most people translates to indoors-without-a-flash.

This is one of the best explanations of max. aperture and what it means practically in shooting terms: What is maximum aperture and why is it so important?

[sk66]

"Fast" is a relative term. F/4 is "fast" for a long lens (400mm and up). F/2.8 is "fast" for shorter zooms (28-70mm, 70-200mm etc). And F/2.0 and under is "fast" for shorter prime lenses (50mm, 85mm etc).

It's "a fast lens" if it lets in a lot of light (has a large max aperture) relative to other similar lenses.

[Algernonep]

Originally Posted by Raoul Isidro

I used to think the word fast in a lens was the speed of money draining from your wallet. The faster the lens, the faster the money drained. I guess, in a way, it still applies today, but I'm sure the rest of the people in this forum will explain it heaps better than this...

That's funny... I have notice that the price do drain you wallet price fast...

I'm saving up for a few fast lenses. It may take a while but I do want...
14-24mm f/2.8, 24-70mm f/2.8, and 70-200mm f2.8