What does "fast" mean?

[srtgray]

Sorry for sounding like a complete n00b, but when people refer to a lens as "fast", are they talking about wide aperture (so the shutter speed is faster) or faster AF response? Or is it sonething else?

[RocketRick]

Sorry for sounding like a complete n00b, but when people refer to a lens as "fast", are they talking about wide aperture (so the shutter speed is faster) or faster AF response? Or is it sonething else?

They mean that the maximum aperture is wide (low number), so that they can use a faster shutter speed in the same light.

- Rick

[srtgray]

Thanks!

[jap]

Of course, the fast-ness of a lens is relative to its category. If we use the 35mm camera lenses as our guide, then we can categorize fast lens speed for the following effective focal length's as:

20mm-21mm (Fast = F/2.8)
24mm-28mm (F/2)
35mm (F/2)
50mm (F/1.4)
75mm-105mm (F/1.8 - F/2)
135mm-200mm (F/2.8)
250mm-300mm (F/2.8)
400mm (F/4)

[srtgray]

So is a 4/3 200mm lens at f4 considered fast?

[jap]

So is a 4/3 200mm lens at f4 considered fast?

According to the listing I provided, yes. Of course, that listing is based on equivalent focal length (efl) 400mm lens being considered fast at F/4. The 4/3's 50-200mm zoom (efl 100-400mm) is certainly considered fast at F/2.8-3.5.

[srtgray]

Coo, I'm learning lots here Thanks.