when someone says "fast lens"...

[jerseygirl]

...what does it mean?

 

[shingfan]

"fast lens" is usually refer to lens with large aperature (small f number)

f/2.0 is larger (faster) than f/4.0

the larger the aperature...the faster you can capture images

 

[Digital Matt]

the faster you can capture images

It doesn't really have anything to do with capturing images faster. It allows the usage of a faster shutter speed, because you are able to let in more light vs a "slow" lens. Fast lenses are useful when photographing sports for the ability to use a bit faster shutter speed. They are also useful for low light photography.

 

[fmw]

Lens "speed" depends to a large extent on the focal length of the lens. The maximum aperture is a function of the physical size of the front lens element so the longer the lenses get, the bigger those front elements become to maintain the same maximum aperture. What is fast at one focal length might be pretty ordinary at another. As an example, a 50mm f2 lens would be considered fairly slow as 50mm lenses go. A 135mm f2 would be considered quite fast. A 500mm f2 would be so extreme and expensive that nobody manufactures them.

Basically, the term means "faster than typical lenses of that focal length." Fast lenses are more expensive. They are harder to design and manufacture because the larger front element creats more aberrations to correct just by virtue of its size. They are also larger and heavier. There is price to pay for the larger maximum aperture but most of us are willing to pay it for the flexibility in exposure and depth of field control.

 

[shingfan]

It doesn't really have anything to do with capturing images faster. It allows the usage of a faster shutter speed, because you are able to let in more light vs a "slow" lens. Fast lenses are useful when photographing sports for the ability to use a bit faster shutter speed. They are also useful for low light photography.

you capture image faster in a sense that with larger aperature you can use faster shutter speed for hte same exposure....of course it doesnt physically capture the image faster...dont pick on me MATT....

 

[jerseygirl]

thanks for clearing that up!

when i think speed i think shutter, hence the confusion...

 

[Digital Matt]

when i think speed i think shutter, hence the confusion...

You are correct, and that's actually what's happening. Fast lenses allow the shutter speed to be faster than "slow" lenses.

Shingfan: Technically, the faster the shutter speed, the faster you capture the image, this is true, but it just confuses the original poster, and is really not what is meant by "fast" lens. Nobody buys fast lenses so they can take pictures faster. They buy expensive bodies with motor drives to take pictures faster.

 

[usayit]

Matt.. btw.. nice avatar. Looks james bondish with some type brain fryin weapon that only Q could invent.

 

[Digital Matt]

Thanks usayit