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hello all,
excuse me for this really newbie question :$
I have a confusing question that came into my mind after reading about aperture and shutter speed. it's a fact that wide aperture like 1.4 is used in low light. what happens if we used it in a normal or bright light and increased the shutter speed? and why would we need higher f stops?
In a nutshell, Depth-of-field (the area that's in focus in front of and behind the subject).
"Fast Glass" eg lenses with a max aperture of F2.8 or lower let in a lot of light - but - the plane of focus may be only a few millimeters deep - so most of the shot will be out of focus. Also - when working with strobes - you often can't have the shutterspeed go above 1/125th.
Hope this helps :)
thanks you. why it is called "fast lens" ??
They are called "fast lenses" because, due to the much larger aperture capabilities, they can be used with a faster shutter speed (therfore, "fast"). There is really nothing in the lens itself that is "fast".
This is not to be confused with references to "slow to focus" which is not the same thing. That is more to do with the mechanical focus drive system in the lens. Having said that, usually a lens with large aperture ("fast lens") makes it easier for the camera to autofocus (and also can make it easier for the user to manually focus as well due to a brighter viewfinder and smaller dof while focusing).
Roger
Here's a video that shows a good example of how a lens' depth of field is effected by it's aperture from a variety of distances, and how depth of field is effected by the distance from subject (soda can). As you watch the video, pay close attention to the foreground and background as the aperture closes down. As the photographers gets closer to the can, will noticed a change in the quality of the back ground blur (aka Bokeh effect) as well. You will also find helpful info too.
http://www.youtube.com/watch?v=uRJMisfK_-Q
thank you rogerb. and thanks Amberglass that was helpful
Sometimes, if you don't want to increase the ISO, when you have a fast moving subject your only option is to open up the lens in order to achieve a suitable shutter speed; but as others have mentioned, you do run the risk of a shallow depth of field.
Also, most of the affordable lenses are a bit on the soft side when fully open.