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View Full Version : Stepping down the Aperture



NWcityguy2
11-05-2006, 05:47 PM
I'm new to the dslr scene and something I've been wondering about is the aperture/sharpness relationship. For example my 50mm f/1.8 gets very sharp when I shoot it at the aperture of 4 or 5.6 as compared to 1.8. What I can't find though, is what exactly causes these two things to effect each other?

Also, and I know I didn't pay the world for my lense, is there anyway to get very sharper pictures at or near the max aperture? It would be nice for shooting indoors, which I find myself doing on a regular basis because it is so cold outside.

Thanks

Adam

cwphoto
11-05-2006, 08:03 PM
I'm no optical physicist, but it's mainly due to lens aberrations near the periphery. Stuff like dispersion, chromatic aberration, astigmatism, coma etc are harder to correct at the edges of the lens. ;)

toriaj
11-06-2006, 08:02 PM
I'm new to the dslr scene and something I've been wondering about is the aperture/sharpness relationship. For example my 50mm f/1.8 gets very sharp when I shoot it at the aperture of 4 or 5.6 as compared to 1.8. What I can't find though, is what exactly causes these two things to effect each other?

It's the same principle as squinting your eyes to see sharper. I think that it gives less room for the light to bounce around, creating blur? (I'm no pro here)


Also, and I know I didn't pay the world for my lense, is there anyway to get very sharper pictures at or near the max aperture?

You should still be able to get the focus point in focus when using a large aperture. It's just the background of the photo that is out of focus. Many shots look better that way. (I want to be sure. When you say max aperture, you mean largest aperture, as in 1.8, right?) If your focus point isn't in focus, perhaps you have camera shake. A tripod might fix that.

In general, though, if you want the background to be in focus, use as smaller (larger #) aperture.

RogerCicala
11-07-2006, 03:28 AM
A lot of lenses, most really, aren't quite as sharp even in the center with the aperture wide open. Stopping down even a little can make a big difference. My own experience is my 50mm 1.8 isn't sharp until about f 2.8.

toriaj
11-07-2006, 06:43 PM
*I stand corrected.*
Thanks, RogerCicala. I'll try that with my lenses, too.