Fast lens

Harpua · Jan 29, 2006

I have heard the term fast lens a bunch since being on this forum, but I am not sure I know what it means. I think it has something to do with f numbers, but I do not have a good grasp yet on those either so I was hoping someone could give me a good simple definition of what makes a lens fast (or slow). Thanks.

Polygon · Jan 29, 2006

The lower the minimum f-number the faster the lens. A low f-number means a bigger aperture which lets more light coming in. Having more light in the same time means that you can user shorter shutter-speeds (or faster shutter-speeds from which the word "fast lens" orginates I think).

Harpua · Jan 29, 2006

Oh OK I think I get it. So the faster the shutter speed can go which is in direct relation to the lower the f number gives you a fast lens. Thanks Polygon.

'Daniel' · Jan 29, 2006

Oh OK I think I get it. So the faster the shutter speed can go which is in direct relation to the lower the f number gives you a fast lens. Thanks Polygon.

Maybe I misunderstand you but I don't think you have quite got it. The shutter speed is determined by the body and the minimum shutter speed does not change depending on the lens you use.

A fast lens means it has/ can have a large aperture (lets in alot of light). Shutter speeds are not involved. Unless you mean the shutter speeed can be faster and the photo still be correctly exposed then yes I know what you mean.

Harpua · Jan 29, 2006

OK I think I was making it more complicated then it needed to be. So basically, the smaller the f number, the faster the lens. And that will allow you to use a faster shutter speed if your camera allows that.

'Daniel' · Jan 29, 2006

http://www.luminous-landscape.com/tutorials/understanding-series/understandexposure.shtml

Digital Matt · Jan 29, 2006

Yes, fast lenses have a wider maximum aperture, to allow more light in, which allows for a faster shutter speed, which can come in handy in low light situations, or when freezing motion.