The f5.6/f4 trick (for best sharpness)

[mrbrycel]

I had always heard that the focus point of a photo shot at f5.6 or f4 is supposed to be sharper than any other f-stops. I never noticed a difference when shooting 35mm stills, because the quality is always pretty amazing at any f-stop.

But the last project I shot on my HVX/Letus/Nikkors, I shot all fully open (both the HVX's iris and the Nikkor's), and I noticed that the focused areas were still a bit soft compared to what I get with the HVX's stock lens, but also softer compared to some HVX/Letus/Nikkor stuff I've seen other people shoot.

I recently heard that if you keep both the HVX's Iris and the 35mm lens's iris at f5.6 or f4, It will be the sharpest it can possibly be. Has anyone tried comparing this? Is it true?

 

[ryvac]

yes, most lenses are sharpest between f4~f8
the sweet spot is different on each lens so some photographers do a shoot out first and test where the sweet spot is for each lens.

 

[Huy Vu]

Stopping down the SLR lens have a very definite effect on sharpness, although the camera lens is less so.

This shot was taken with an 85mm f1.2 at full wide. Note how much softer it is compared to the one below it, where the lens has been stopped down to 5.6.

 

[steve phillipps]

It's because of diffraction. This is an optical effect that limits the maximum possible sharpness and is a function of the size of the iris opening vs the size of the chip/film.
It's becomes more of an issue the smaller the chip size. So with a piece of 10x8" film you can use f64 and still be OK, but on a 1/3" chip the diffraction limit is probably reached around f5.6 or even less. This is why you don't notice it with 35mm stills, you're OK down to about f11 or so.
So on a small camcorder the upper limit is set by diffraction to about f5.6, while the lower limit is about f4 because the lenses are quite cheap and don't perform great until they are stopped down at least a stop from wide open.
Steve