How much light?

prodigy2k7 · Jul 11, 2008

EF 70-200mm F/2.8 IS USM vs EF 70-200mm F/4 USM in lighting...

When just looking at stops, while the F/2.8 IS lens is opened all the way to F/2.8 and IS is turned on, Does it allow you to take a picture equilivant to a lens of F/1.0 with no IS?

Also, does the F/2.8 IS allow 4 stops more light (3 stops for IS then another stop for bigger aperture) than the F/4?

Sorry I dont know how to ask questions like those. I hope you can understand what im asking. Am I on the right track?

Im trying to understand how ISO/shutter/aperture work together in f-stops and whatnot... Also looking at lenses... and how they work with different lighting conditions...

Big Mike · Jul 11, 2008

IS doens't allow any more or less light...it just helps to compensate for camera shake (blur) that happens with slower shutter speeds.

Don't think of IS in terms of aperture or light...think of it in terms of shutter speed and camera shake.
Where you might be limited to 1/180 to get sharp shots (shooting hand held)...you could possibly shoot at 1/25 and get similarly sharp shots, when using IS. You are getting the same amount of light for proper exposure but you can use smaller apertures and lower ISO settings.

Each person is different in terms how steady they are....so camera shake is a personal thing.

prodigy2k7 · Jul 11, 2008

yes I know, but im talking about f-stops when referring to aperture just because... I just used aperture as an example...

Garbz · Jul 11, 2008

Well as far as preventing the shake yes that's the way it works. What Mike was pointing out is that although camera shake is prevented suppose you take a photo of a person walking at 1/5th with a 35mm IS lens (quite possible), the subject would be a blur even at slow speeds because IS only compensates for the camera motion.

So while you can hold the camera 4 stops steadier, IS / VR does not make it equivalent of 4 stops better because your subjects still have to obey the shutterspeed.

e.g. you can use a f/1.8 lens in a standard indoor to take a photo of an average 3 year old, but an f/4 lens with VR will not suffice here unless you slip them some sleeping pills.