Most lenses
will not give you their best performance when wide open, and
thus will generally give you sharper images at the area of
“critical focus” - the point of focus, not factoring in depth of
field, when stopped down about 2 stops. Once you reach a
certain point your images do not get any sharper as you continue
to use smaller apertures. If you go too far, then diffraction
becomes a significant problem. This is the reason that again,
as a general rule, the “sweet spot” for most lenses in the f/4
to f/11 range. This of course is dependent on the quality of
the camera and the lens. Having said that, some of today's
quality pro lenses perform optimally when wide open.
LENS QUALITY
Top quality lenses are vital to creating “tack sharp” images. This usually means buying the Pro-grade lenses by the manufacturer of your camera. There are a lot of good third party lenses out there and some will give you some good results. But if you are looking for better than good, then your best bet is to go with the camera's brand name. There may be a few exceptions, but very few.
Top quality
lenses are much more expensive and there is a very good reason
for that--they are that much better. They will generally give
you better image quality, faster auto focus speed, better
detail, sharper focus at all apertures and focal lengths (if it
is a telephoto lens), minimal image distortion, better quality
of color, flare resistance, vibration correction, and build
quality.
Copyright © Brad Sharp. All rights
reserved.
1/500 sec. @ f/2.8 ISO 800 Lens: EF 70-200mm f/2.8L IS USM @ 155mm - Hand held
For this shot
I was not able to use the “sweet spot” of the lens (f/5.6)
because the lighting was low. I needed the shutter speed
to be fast in order to shop the action, which required me to use
a high ISO and a wide open aperture. This is one of those times where you won't
be able to get a “tack sharp” image. The priority shifted from
getting a "tack sharp" image to a priority of stopping the
action with enough light to get a good, usable image. However,
with my camera (Canon 5D Mark II) and an L series lens (Pro
grade), I was able to get a much, much sharper image than if I
had used a 'consumer' quality camera and lens.
