camerapapi Loc: Miami, Fl.

I read Ken Rockwell's article and it is too complicated for me. With a big format cameras small apertures work well because those lenses are not very fast. I would not say, and I am no expert in optics, that f13 is the optimal aperture of a lens.
It is well known since the beginning of photography that larger apertures are sharper than smaller ones because of the lack of refraction. It is also well known that with large apertures lenses tend to loose resolution at the edges of the images. It seems to me there is a compromise here which is even more compound when we use zooms of variable apertures. In general most lenses are sharper 3 stops closed from their maximum aperture.
Diffraction is something I have heard a lot of during the years. I have no issues using f16 in many of my shots when I need depth of field. I enlarge to 13x19 and my eyes have not been able to tell a significant difference when using 35mm type cameras or cropped sensors. I never was able to tell the difference either when I was using medium format film cameras.
I do not use depth of field which by the way is a rarity today with modern lenses but I do use many times when in doubt the depth of field preview. To me and it is my personal opinion, it is more accurate than depth of field.
Many photographers become obsessive with sharpness and many do not seem to understand that sharpness depends a lot on how we use our cameras. The most professional camera and the sharpest lens will not produce good results if we do not do our part.
Today the majority of the lenses made are of excellent optical quality. I consider f8 as an excellent alternative to great photographs regardless of the lens in use since most of the time f8 happens to be in the middle of the aperture range.

selmslie Loc: Fernandina Beach, FL, USA

It's too detailed (eyes glaze over) to be of much use to anyone but it might make a good read if you have the time to pay attention and read it critically.

That's pretty much what I do by default for full frame (24x36 mm). I only deviate from that to get a shallower DOF for closer focus distances or more DOF for landscapes. That keeps things simple.

For medium and large format I am usually looking for as much DOF as I can get because the subject matter is different so I usually work at about the diffraction limit and use longer exposures on a tripod.

Mark7829 Loc: Calfornia

Like I said, the manufacture like Nikon has published a listing of their lenses and their sharpest aperture. Chromatic aberration, distortion, vignetting interfere with sharpness while a lens's coating enhances. Sharpness is not a value in itself but rather a combination of values that are at optimum at a a tight range of aperture and usually low. Almost all lenses are sharp at center but that does not make it a good lens.

John_F Loc: Minneapolis, MN

All light when passing an edge refracts, each wavelength by a different amount. Whether that is noticeable depends on factors such as the leaves of a diaphram. The higher the f-stop the smaller the diaphram and the more readily the diffraction will be noticeable. The one factor that is irrelevent is the light receiving medium, be that a projection screen, camera film, or digital camera sensor.

selmslie Loc: Fernandina Beach, FL, USA

If you can find that information before you buy, it can help. If you already own the lens you may have no choice other than to test it yourself.

It is probably safe to assume that all decent lenses perform within the ranges that we have discussed here.

Mark7829 Loc: Calfornia

A good lens is much more than sharpness, and then it is up to the photographer to use light and composition to achieve the best results. Even an iPhone in the hands of an experienced photographer will do better than the sharpest lens in the hands of a amateur.

http://www.ippawards.com/2015-winning-photographs/

selmslie Loc: Fernandina Beach, FL, USA

Now we are really getting far from the OP's question.

jimmya Loc: Phoenix

I'm not challenging the article just stating... with my go to lens, Canon 28-200, my sharpest is f/10 especially with long (time) exposures at night.

Mark7829 Loc: Calfornia

Not really. Many are so focused on sharpness and have said that if their lens were sharper they could take better pictures. That is not reality. Technology will not lead to better pictures as much as a mastery of light and composition. In fact so many award winning images are not sharp at all. Art trumps technology every time.

folkus

Hi Apaflo - thanks for attempting to bring the duscussion back to best sharpness A C R O S S a depth of Field. Much apprecisted. Folkus.

Retina Loc: Near Charleston,SC

This is what I learned, and seems to make sense. There is always some diffraction past a partially stopped aperture. At larger apertures, the amount of non-diffracted light through the open part of the lens is great enough to mask the cloudy parts of the image caused by diffraction. F/64 on a normal lens for an 8X10" camera presents a much larger lens opening than, say, f/32 on a similar lens for a 1x1.5" camera, while light's wavelengths are the same for both. Wavelength interacting with the physical dimensions of the lens/iris system are directly involved with the problem of diffraction. Large format photographers were also concerned with diffraction but on a different scale because their lenses were bigger for the same filed of view than with the miniature cameras used by most of us.

RRS Loc: Not sure

As for Ansel Adams , f/64 but what lenses did he use and what was the max aperture of those lenses. I know that he didn't use "fast" lenses. I've shot with 4x5,5x7 and 8x10 cameras and the old lenses were time consuming but also fun to work with. It had to be sharp SOOC because he didn't have sharpening available as we do today.

n3eg Loc: West coast USA

Follow the Cambridge chart or test it yourself. I checked my camera and lens, and found that with m4/3 and an adapted Canon lens it was exactly what the chart said. Even a half stop above f/5.6 I could see diffraction. From there down to f/1.8 it was fine. I used a towel on a wall for the test.

selmslie Loc: Fernandina Beach, FL, USA

Of course not. The OP was simply asking at what point the image becomes sharpest. I don't think he was assuming that sharpness is the ultimate goal for a good image.

Sharpness across the entire image continues to improve (along with several other optical qualities) as you stop down until diffraction starts to become visible.

selmslie Loc: Fernandina Beach, FL, USA

Adams was using large format film and correspondingly longer lenses. A normal lens for 4x5 is about 150-180 mm and it is twice that for 8x10. At f/64 a 300 mm lens has a diameter of 300/64, 4.7 mm. A 50 mm full frame lens at f/16 has a diameter of 50/16, 3.1 mm. So Adams would have had less diffraction at f/64 that you would with a full frame normal lens.

You may not recall that high acutance developers increase the appearance of sharpness in a negative.

Diffraction is actually related to the size of the negative but for digital it can also be affected by the size of the pixel at the sensor. See http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

The smaller your format the sooner you will observe diffraction. A m4/3 sensor is significantly smaller than full frame.

A 24x36 film format is not diffraction limited at f/22 but a 24 MP sensor is limited at f/16 and a 36 MP sensor is diffraction limited at f/11.

Regardless of the calculations, diffraction does not suddenly happen. Like most lens phenomena, it comes on gradually as you reduce the aperture.