Sharper Picture stopped down?

Is is true that if you have an f2.8 lens and you stop it down to say f4 the picture will be sharper? To me it does not sound correct but I've read it a couple of places and perhaps misunderstood the writers.

Hugh

Yes. Most lenses have a "sweet spot" that is a couple of stops down from wide open.

All lenses are a bit softer wide open. They're also usually a bit softer at f/16-f/22 due to diffraction.

Yes, as runninmann said - usually stopping down by about 2 stops will be about the 'sweetest' spot on most lenses.

i find my 17-55 very sharp at f3.2! but yes, stopping it down will help.

"Wish List: Enough talent that it matters which lenses I use."

That truly is an excellent point. I have been contemplating either a Canon 70-200mm f2.8L IS or the brand new 70-200 f4.0L IS. The f2.8 is very heavy at 3.5 lbs as well as expensive. I'm trying not to let price be a factor.

Sigma 70-200 f/2.8 ?

HughScot wrote in post #2022056
"Wish List: Enough talent that it matters which lenses I use."

That truly is an excellent point. I have been contemplating either a Canon 70-200mm f2.8L IS or the brand new 70-200 f4.0L IS. The f2.8 is very heavy at 3.5 lbs as well as expensive. I'm trying not to let price be a factor.

As an amateur SLR photographer for almost 30 years, I've never been totally satisfied with any of my pictures. There's always something in the composition or the exposure or (back in the film days) the processing that left me wanting. So, my wish list is to be in a position to say, "Man, I nailed it. If only I had the lens, it would have been perfect.

Hugh, you have read the 'truth' about lenses generally performing best about 2-3 f/stop from the widest aperture. Another point I will add, however, is that a truly good lenses will perform even wide open at levels which often exceed the best that a mediocre lens can do stopped down 2-3 f/stops!
For example the Canon 70-200 vs. the Canon 18-55 (yes, it is a bit unfair to compare different lenses of focal length ranges but...)

The 70-200 when wide open has MTF ratings at 70mm of 1952 center, 1880 edge
The 18-55 when stopped down has MTF rating at 55mm of 1719 center, 1417. In other words the 18-55 at its best is worse than the 70-200 at its worst!

My 70-200 f/2.8L IS and 17-40 f/4L both are "sharpest" at F8...

I believe all lenses are sharp as can be at F/8 or so

calicokat wrote in post #2022310
I believe all lenses are sharp as can be at F/8 or so

Not always! The infamous kit lens performs best at f/5.6 at the short end and middle of the focal length ranges, and at f/11 at the long end or its range!

I stand corrected

calicokat wrote in post #2022661
I stand corrected

I think a good generality is that most lenses perform quite well at f/5.6 and f/8. It's 'best' performance may actually be at another f/stop, but you cannot go wrong cranking in f/5.6 or f/8!

But my 85L is sharp as a tack at F/2.8 j/k don't want to get anyone too excited