selmslie Loc: Fernandina Beach, FL, USA

About three months ago I did a lot of lens testing, specifically for sharpness, using a Z7 (45.7MP) which meant that I used an adapter for nearly all of them. I thought that the higher MP of the Z7 would make it easier to see the lens sharpness.

I used the entire range of aperture settings to try an find each lens's visibly sharpest aperture and the point where diffraction starts. It was not easy to see the change from one f-stop to the next. I suspected that the Bayer array might be why.

Last week I bought a Sony FE Carl Zeiss Sonnar T* 55mm F1.8 ZA and to save a little time, I tested it on my 24MP Sony A7 II monochrome. I found that, with no Bayer array interfering with the image, it was much easier to see the difference between f-stops. The sharpest apertures were f/4 through f/8 and diffraction clearly starts to show at f/11 (see example in next post).

So I retested most of my other lenses (all prime) and found that I could get a better comparison with the 24MP monochrome than with the Z7. Nearly all of them from a 28mm Zeiss ZM through a 135mm Leica Elmar produced the sharpest images at f/5.6 or f/8 with the latter being better for the 90mm and 135mm. All of them clearly started to show diffraction at f/11.

I'm not going to retest the ones I skipped over because I think that I now have information I can apply to any full frame camera. Besides, there is no way to mount a Z lens (16mm flange distance) on a Sony (18mm flange distance) and focus at infinity.

selmslie Loc: Fernandina Beach, FL, USA

Here is what I found with the test for the 55mm lens. I was able to replicate this with all of the other lenses I tested.

f/8 vs f/11, seconds apart. Best when viewed at 100%.

(Download)

TriX Loc: Raleigh, NC

I can see the difference (and btw, this is a good subject for the test) looking at the reflection of the fence in the water, water droplets, shingles on the roof, trees… it’s not huge, but it’s there. Post another at f16, and it will be more apparent.

selmslie Loc: Fernandina Beach, FL, USA

Yes, it keeps getting softer beyond f/11.

The fence, bricks and shingles are a good distant target at about 150 yards. This is a 100% view of the center of the screen.

What you can't see are the left and right edges which look best in all cases at f/8. The bottom (grass) is too close and the top (sky) has no detail other than a random bird.

This is a 100% view of the center of the screen.

(Download)

camerapapi Loc: Miami, Fl.

I hope you understand that a 100% crop enlargement will not fit on any of the walls in your house. I am sure you understand the center of an image, as a rule is the sharpest part of the photograph.
Diffraction is common to all lenses and we all know it begins to show its face at around f11. The more we close the diaphragm of the lens the worse the results.

Now, should we refrain from using f11 and f16? Obviously not. Zooms with maximum apertures of f5.6 perform better at around f11 or f16. They are not the best performers at f5.6. For prime lenses and according to my humble experience, the mid range of apertures are usually the sharpest. Only one problem with it, when we need depth of field we have to go to the smaller apertures and forget about diffraction. Adding some sharpness and looking at the images at viewing distance those images look very nice.

I cannot speak on behalf of anybody else but knowing that diffraction is there I have never been too concerned about it. I never enlarge to 100% and I never pixel peep. As a matter of fact some of my best enlargements have come when I used f16.
Just my personal opinion.

Jim Bianco

99% of the time I shoot at F/8 to F/10 to get the sharpest photos, that works for me.

Tomfl101 Loc: Mount Airy, MD

In addition to your informative test, I would point out that one rarely ever needs to shoot at apertures below f-8. I suppose more with macro photography but almost never in landscapes. So if depth of field is a critical need, focus stacking would be the best alternative.

SuperflyTNT Loc: Manassas VA

I also think the fact that he had trouble seeing the difference on the Z7 is telling. If you have to go to great lengths to test it how much of a problem is it?

selmslie Loc: Fernandina Beach, FL, USA

Whether or not you should be concerned with diffraction depends on your subject matter.

Since I shoot landscapes I use only prime lenses. I don't want diffraction and I want clear details throughout the image with no visible chromatic aberration (CA).

When the subject is flowers the background is out of focus where sharpness and CA can't be seen. But the edges of the flowers would show any defects.

A zoom that looks better at f/11 or f/16 is probably not that sharp to begin with so you are not likely to be aware of the diffraction and CA.

The only zoom I use is the Tamron 150-600 f/5-6.3 G2 and it's sharp enough near the center where the subject is located. I don't care about the edges. F/8 gives me plenty of DOF. Besides, I only use that lens on my 16MP Nikon DF.

selmslie Loc: Fernandina Beach, FL, USA

In fact, if the subject is landscape with flowers in the foreground, stacking will give you an image without diffraction or CA. It's easier than stacking a macro subject.

And you can get a really high resolution image with a stitched panorama.

selmslie Loc: Fernandina Beach, FL, USA

It's only a problem if you recognize it and understand the implications.

The fact that the Bayer array was masking the problem is an indication that was complicit. The Bayer array itself significantly cuts the resolution (by about 50%). That hides the diffraction that might have its source in an aperture that is too small. So you get garbage in, garbage out - raw data with hidden diffraction that is softened further during the demosaicing process. But if you minimize the diffraction in the raw file you can reduce the damage.

Knowledge is power. Ignorance is bliss.

TriX Loc: Raleigh, NC

A blanket statement that an f5.6 zoom performs better at f11 or f16 isn’t always accurate - some zooms are actually sharpest wide open. Diffraction is both real and the aperture where it becomes noticeable also becomes lower as the sensor format decreases in size. If you really need f11 or f16 for DOF and stacking isn’t an option, then you may have to live with it, but throwing away sharpness that you paid big $ to get in a lens is an unnecessary waste if you have a choice.

SuperflyTNT Loc: Manassas VA

I wouldn’t say garbage in, garbage out. If you’re shooting digital color the Bayer array is the nature of the beast. And I’m not saying just to ignore it, but for me it’s a little farther down the list of considerations when shooting. That being said I’ve never shot my Z7 any higher than f/11. There’s just no need. And if I’m shooting a landscape with foreground elements closer than the front of DOF for hyperfocal distance I would focus stack. With my OM-1 I don’t usually go above f/8.

selmslie Loc: Fernandina Beach, FL, USA

Garbage may be an overstatement. If you want color you have to live with the effects of a color filter array (CFA). The only way to get around it is with more megapixels and/or a larger sensor.

The effect is clearly visible if you have a sensor with no CFA. I can get the same sharpness from a 24MP monochrome sensor as I can get with the Z7 - before applying any sharpening or clarity adjustment in post.

Sharpness is not always the most important quality of an image but it would be a shame if it were a noticeable defect.

mwsilvers Loc: Central New Jersey

It really depends on the widest aperture of your lenses. While not a rule, generally most lenses are at their sharpest two to three stops from wide open. Fast f/1.4 primes often max out in sharpness at f2.8 to f/4. Beyond f/4 there may be an impression of greater sharpness because of the increase in depth of field, but it is often just an impression and not a real increase in sharpness.

Variable aperture zooms with maximum apertures of f/3.5 to f/4.5 off and have a sweet spot of f/8 to f/11 as you have found.

My Voigtlander 35mm and 23mm f/1.2 manual focus primes max out in sharpness at f/2.8 to f/4. By f/11 diffraction is already visible.