fast lenses quick question

[hagz]

i see the term Fast lens applied to lenses with low (wide) apertures f1.4 to f2.8 and i sort of get the jist with it but what does it really mean?

does fast mean low (quick) shutter speeds or fast in focussing? lol

i know this will not drastically change my photography as i do not own such a lens but i just like to know these things.

[ap4a]

Faster as in allowing faster shutter speeds.

[hagz]

cool so i was not a million miles away and i see why that is good for low light levels.

[AndrewKulin]

Faster auto focus as well as a fast lens allows more light in which aids speed of auto-focus.

[ianpinion]

Originally Posted by AndrewKulin

Faster auto focus as well as a fast lens allows more light in which aids speed of auto-focus.

Well it allows more light to pass through it in less time because of the wider aperture value.

[Drew Smith]

Originally Posted by ianpinion

Well it allows more light to pass through it in less time because of the wider aperture value.

Yup - as Ian says, larger aperture more light, more light more leeway in shutter speed, ISO adjustments.

This was shot on a horrible rainy cloudy day in February. Now add to that the location of the shot, tall pine trees on every side in a forest. Plus the shot was of fast moving animals and you have a recipe for blurred pictures. So the lens set at f2.8 allowed a ss of 1000/sec and and combined with an ISO of 6,400 the shots were possible.

Of course if the idiot with the camera had remembered to change the focus tracking sensity then the front two dogs would have been in focus instead of the second two! :

[hagz]

i am looking at that photo for all the right things but all i can think is



HOW LONG ARE THOSE DOGS TONGUES LOL

[AndrewKulin]

Originally Posted by Drew Smith

Of course if the idiot with the camera had remembered to change the focus tracking sensity then the front two dogs would have been in focus instead of the second two! :

Isn't there a setting for that?

[hagz]

to me the fact that the two front dogs are ever so slightly out of focus gives the impression they are really lunging at you

[KeithT]

Funny old thing, the science behind lens tecnology. The wider the aperture (more light allowed through) the narrower the depth of field and the harder it is to control focus. The narrower the aperture, the more likelihood of diffraction (see here for explanation http://www.kenrockwell.com/tech/diffraction.htm)

The real secret behind pin sharp images is threefold: 1, make sure you have good light, 2, always use a tripod for absolute sharpness, 3 set your aperture its optimum for your lens. A rough guide to this is to use an aperture which is between 2 and three stops up from widest.