Lens speed: Not always the best choice

RichA wrote:
People buy fast lenses for 2 reasons:
-The want the speed to capture action.
-They want the shallow DOF afforded by such lenses.

For for the first reason, speed is not always the best choice.
Shooting at a higher ISO sometimes works out better than using a lens
wide open and once you determine that it does for a specific lens,
then there is generally no reason to shoot a specific subject at the
wider aperture. The benefits are better image quality (fewer image
aberrations), possibly more accurate focus and the potential to use a
much cheaper lens. The downside is noise and giving up shallow DOF.

Here is an example of a shot at 800 ISO with a lens wide open and 1600
ISO with the lens stopped down. Shutter speeds were the same, so you
aren't giving that up.

The trick is to determine which lenses fall into this category.

http://www.pbase.com/andersonrm/imag...08342/original

Except that ISO 1600 at f/4 the same exposure as ISO 800 at f/2

David

On 7/10/09 11:49 AM, in article
, "David J Taylor"
wrote:

RichA wrote:
People buy fast lenses for 2 reasons:
-The want the speed to capture action.
-They want the shallow DOF afforded by such lenses.

For for the first reason, speed is not always the best choice.
Shooting at a higher ISO sometimes works out better than using a lens
wide open and once you determine that it does for a specific lens,
then there is generally no reason to shoot a specific subject at the
wider aperture. The benefits are better image quality (fewer image
aberrations), possibly more accurate focus and the potential to use a
much cheaper lens. The downside is noise and giving up shallow DOF.

Here is an example of a shot at 800 ISO with a lens wide open and 1600
ISO with the lens stopped down. Shutter speeds were the same, so you
aren't giving that up.

The trick is to determine which lenses fall into this category.

http://www.pbase.com/andersonrm/imag...08342/original

Except that ISO 1600 at f/4 the same exposure as ISO 800 at f/2

David
That would be Ÿ2.8