Are Modern Lenses At Their Best Wide Open?

Hank wrote: "I wonder now about the idea that lenses are best stopped down two stops from wide open. That certainly is true of lenses from the film era, but I can’t help but feel that today’s (better) lens designs are made for wide open use. It’s possible this was done to appease the bokeh-fanatics, but on some systems, such as Micro 4/3, it would seem to be a requirement, no?"

Mike replies: A lens is said to be "diffraction limited" at the widest stop at which diffraction has the largest negative effect on image quality, the point at which stopping down further only increases diffraction* rather than further minimizing aberrations. That aperture is also known as the optimum aperture. A "diffraction limited lens" is diffraction limited at its widest stop. These are rare.

As an illustration, take a look at Imaging-Resource's lens test of the Nikon 24mm ƒ/1.4G. At the link, go to "Lab Test Results" in the upper right hand side of the page. Then click on "Nikon D3x." That means you're looking at their test results for the lens on a full-frame camera. Now, run the aperture slider up and down the range. The lower and flatter the colored part of the 3-D performance map, the less blur. As you go up and down the aperture range, you can see the performance gets better as it is stopped down, until ƒ/4—that's where aberrations are minimized. After that, the graph of performance begins to rise again—that's diffraction kicking in. So according to this test this lens's optimum aperture is ƒ/4, three stops down from wide open.

You'll also note that the results for ƒ/4, ƒ/5.6, and ƒ/8 are quite close to each other, which is why photographers talk about "the middle apertures" as offering best optical performance.

Note also that the middle part of the field is still pretty good with this lens even wide open. Looking at only the middle of the field is what leads some photographers to think that some of their lenses are just as good wide open as stopped down.

You're right, however, Hank, that modern lenses—especially slightly longer ones, especially ones for smaller formats—do suffer from fewer aberrations at wider apertures, and can be very good wide open. Let's turn to the Imaging-Resource test for the recent Fuji XF 50mm ƒ/2. As you run up and down the aperture range for that lens, you can see that its performance is admirably consistent from edge to edge  and through the aperture range (the graph stays pretty flat and doesn't move up and down very much throughout the range). However, even with that lens, you can clearly see that performance improves as you stop down...even if only a little. That lens, too, is diffraction limited at ƒ/5.6—three stops down, same as the Nikkor above.

You'll find that most lenses are technically at their best 2–3 stops down. Even if their performance is very consistent and the differences are slight. You can see the same thing if you have a complete family of MTF tests, for every aperture.

However, there's a bigger difference for photographers, in that some lenses are so consistent that for practical purposes the technical "sweet spot" doesn't really matter. The difference in the Fuji lens's performance at different apertures is minimal enough that you'd be likely to have trouble seeing it with general shooting, especially handheld.

You can easily use such test information when shooting. For example, with the Nikkor 24mm ƒ/1.4G on FF, I'd shoot at ƒ/1.4 and ƒ/2 only if I knew that center sharpness was all I needed. If I needed the whole frame to be critically sharp, I'd know to stop down to the middle apertures. With the Fuji 50mm ƒ/2, on the other hand, I doubt I'd avoid any of the apertures for reasons of optical performance—they're essentially all "middle apertures" in the sense that all apertures would be decently sharp for ordinary pictorial subjects. Except for perhaps those few pictures in which resolution might be critical. In practice, with that lens, you can't see the tiny measured differences between ƒ/4 and ƒ/5.6, for instance, and I wouldn't hesitate to shoot with it at ƒ/16 based on I-R's test info. (But of course the final test is our own results according to our own eyes.)

As to whether you need to stop down for best sharpness, it's seldom a bad idea, but then again with some lenses it's not particularly necessary. The best advice is simply to learn your lenses—check the tests, look at your own pictures, figure out what you might need to do and when, and then apply that knowledge as best you can! (Sometimes in the heat of the moment these things aren't that easy to remember. Having fewer lenses and keeping them longer helps your familiarity with them.)

As an aside, a quick visit to Imaging-Resource's test graph for the Panasonic 12–35mm ƒ/2.8II will show you why I like it.

Mike

*"Diffraction" in lenses refers to the way that rays of light spread out as they pass physical obstacles—in the case of a lens, the edges of the aperture blades. As the aperture gets smaller, the relative percentage of these diffused light rays relative to the area of the total light passing through the glass of the lens goes up. It's also why a pinhole image is always soft—the diffused rays comprise such a large percentage of the light rays coming through the hole. Very small apertures will always show the effects of diffraction. Large apertures actually have more diffraction, but the diffused light is such a small percentage of the overall light coming through the lens that it's not significant.

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(To see all the comments, click on the "Comments" link below.)
Featured Comments from:

Hank: "Thanks Mike!"

Mike replies: Yer welcome.

David A Edelstein: "It's been a while since I've looked at any of those sharpness tests—mostly I shoot with what I shoot with and I don't care about what tests say. However, looking at the tests for the Zeiss 50mm ƒ/1.4 shows exactly why I love that lens: it's very, very weird wide open, gets 'normally unsharp' stopped down to ƒ/2, and then pretty damn sharp at ƒ/2.8 and smaller. Each of those give me specific visual styles I can use for different ideas."

Mike replies: A man after my own heart. Exactly so, and just what I'm talking about—if you know your lenses you can make use of everything they offer, not just their optimal sharpness. It can both help you avoid mistakes and also use their weaknesses to pictorial advantage. A great many art photographers liked less-than-optimal lenses for specific visual properties.

SteveW: "The Nikkor 58mm ƒ/1.4G does not score well with the test chart scores online, and is a controversial lens in that regard: not sharp enough to justify the expense is the primary argument. However, the 58mm is pretty much the reason I stick with Nikon and not try a smaller sensor system.

"The 58mm has interesting characteristics. From ƒ/1.4–4 it is one kind of lens, especially in the ƒ/1.4–ƒ/2.8 range. From ƒ/5.6 and smaller it behaves more like a normal 50mm. To be sure, the 58mm has a wild blur chart on the Imaging-Resource test page: it's my most challenging and fun lens to use, and it won't win any sharpness awards to be sure. That said, I'd probably have switched to Fuji or Micro 4/3 if not for this lens.

"I imagine a lot of folks who read Mike's blog will have similar stories of lenses they are fond of for reasons other than sharpness. In this sense I like Mike's idea of the 'nested' two lens kit. A standard zoom that is nice and sharp and 'normal,' and then a favored prime within the range that does unique things, even if only a really wide aperture or a micro or tilt-shift or whatever strikes one's fancy."

Comments

[s.wolters]

Lenses are in photography like typefaces in typography. You need more than one because they all have their own character. When I want maximum resolution and a long depth of field I prefer my Olympus 30mm f/3.5 macro. When I want beautiful sharp to unsharp rendering my Olympus 25mm f/1.2 is better. Need them both even their focal length is almost the same. Compared to typefaces they differ like the Frutiger and the Trinité. The analytical 30mm f/3.5 macro is usable through the whole range except for the smallest apertures. I estimate it peaks at f/5.6. The flirtatious 25mm f/1.2 is already great when used wide open. It’s sharpness improves slightly at 1.4 and 2.0, but the bokeh will lose a bit of its quality with every stop.

[Rob de Loe]

"The best advice is simply to learn your lenses...". As I'm reading this post I'm processing some images I made to see how a new lens performs. What a funny coincidence.

Each of my lenses behaves differently. I like to know how they behave at various apertures and distances so I can get the most from them. But that's it for testing.

Regarding sweet spots and what not, I'm actually the opposite of a "bokeh fanatic". Is there a name for those of us who suffer from this condition? Anyway, I have some lenses that definitely are softer at f/16 than at f/5.6, but I'll shoot them at f/16 all day if that's what the picture I want to make needs! (Mind you I tested them at f/16 to be sure I'd be happy with the results...)

[Bernd Reinhardt]

I believe that it generally still holds true that lenses are sharpest when stopped down a little, but since perceived sharpness is relative, we tend to perceive the sharpness of a lens more when we see it in contrast to an out-of-focus background.

[Christer]

Testing your lenses is so easy today with digital cameras. Print five ASAF charts on A4 paper, affix them to a wall on an area about 150 cm wide and one meter high, one chart in each corner and one in the middle. Place the camera on a tripod, making sure the the camera is at the same hight as the middle of the picture area and right in front of the middle of the picture area. Arrange for even illumination. Then shoot at the f-stops you want to compare, using Raw and underexpose by one stop. Review results in actual size on your screen using a program like Capture One that allow side-by-side comparisons.

What did I learn from testing? That my Sony and Zeiss lenses for my A7r3 can very well be used fully open. Closing down half a stop improves a little, but then it is often d.o.f. that plays an important role.

[Benjamin Marks]

Excellent explanation, Mike! From an educational perspective, one huge advantage of digital is the potential for instant review of one's lens/camera settings as the effects of those settings appear in the image. Much better than clicking on a Wednesday, developing on a Sunday, and printing whenever you could scrounge darkroom time from a busy schedule.

For my own photography, and I suspect that of many of your readers, the question of a lens' best performance usually takes back seat to the needs of the subject. Or said another way, I approach a portrait of my 83 year-old mother differently than my four year-old nephew. I rarely have taken a picture where I think. "Darn, that's not sharp enough." Usually, if the focus is blown, it's blown and it ain't the fault of the lens, if you know what I mean.

[Gordon Buck]

I maintain that most devices are "designed" and "optimized" for operation at mid-range. Think about it: Suppose you design something and, to your surprise, it operates best at one extreme or the other. Wouldn't you simply extend the range of operation even if the extension was only acceptable and not optimum? Wouldn't the marketing department want this extended range?

[Craig Yuill]

I have a number of Nikon and third-party F-mount lenses, and I find that most of them need to be stopped down at least 2/3 stop to be truly sharp. I would tend to agree that maximum overall quality is reached at around 3 stops from maximum aperture - unless you need shallower "depth of field" or faster shutter speeds.

My 1 Nikkor lenses for the now-defunct Nikon 1 mirrorless system, however, are all very useable wide open. It doesn't surprise me that people are finding that they can use recently-released lenses wide open. I think that this is where the true future size and weight savings will come from in mirrorless systems - without having to stop down to get decent sharpness, photographers can use f/1.8 prime lenses instead of f/1.4 prime lenses, and f/3.5 or f/4 zoom lenses rather than f/2.8 zoom lenses. This kind of trend is more likely to get me to upgrade my glass. Frankly, I find many of the latest fast prime lenses to be ridiculously large. I would much prefer smaller lenses, not unlike the Fujicrons about which you have been waxing so eloquently of late.

[Stan B.]

Frankly, I'm astounded by the performance and edge to edge resolution of certain modern lenses, the Fujinon 14mm (with which you're familiar) and the 18mm on the Ricoh GR, two such examples. I was elated when I just barely got off the shot below, but my heart quickly sank when I realized I had shot wide open... Distance and resolution saved the day (please note, Flickr does seem to add sharpening)!

https://www.flickr.com/photos/19140817@N02/44639220062/in/dateposted-public/

[Herman]

And if I squint when looking thru a camera view finder, the image is sharper than if I remain wide eyed.

[Marcelo Guarini]

Also check the Olympus 12-40mm f2.8 and the 12-100mm f4.0, they are almost at their best wide open, incredible.

[c.d.embrey]

Always use the the right tool is never truer than when picking a lens. A flat-field uber-sharp lens may be appropriate for photographing brick-walls ...for portraits not-so-much. Film-era lenses with curved fields that are only sharp-in-the-center can make beautiful shots. Uncoated lenses provide fill-light due to flare. Don't follow the herd—pick your favorite defects and make magic.

[Kodachromeguy]

Thank you for a nice summary of diffraction and stopping down. My 1949-vintage Leitz 50mm Summitar is an excellent example of a lens whose characteristics change when stopping down. At f/2.0, the edges have some rather serious aberrations, but the center is reasonable. Stop down to f/4.0, and the lens is sharp across the frame, but it has distinct field curvature. The photograph below was taken at f/2.0 in Vicksburg, Mississippi.

https://3.bp.blogspot.com/-XInb0Y-C1uY/UAsQOkWHqJI/AAAAAAAACj8/VW7jIMPm2r4/s1600/P1020097_MLK-Blvd_120721-resize.JPG

[Richard Jones]

"The best advice is simply to learn your lenses—check the tests, look at your own pictures,

I think you have advised this before, which has been my routine for years!

Fred Picker wrote, "Careful photographers run their own tests."

With my new (at the time) 50mm macro lens, I wanted to know how much I can stop down for DOF and still have good detail. The lens has a range from f/2.8 - f/16. Here is the test I created at the time:

http://rsjphoto.net/cam-lens/fe50macro/diffraction/

- Richard

[Joseph]

You are at your best when you write about what you know best. Thanks for this

[Richard Tugwell]

I always wonder about of edge sharpness wide open, and the circumstances in which I might need it... shooting a brick wall in dim available light maybe?

[alan]

My MFT lenses may not be at their very best wide open but they're maybe better wide open than SLR or DSLR lenses were a few years ago or maybe are even now.

I tend to use my MFT lenses wide open especially the f3.5 or 4-5.6 zooms and the results are pretty impressive.

I also have a Sony A7 and 35mm 2.8, 55mm f1.8 and 85mm f1.8 and all are IMO astonishingly good wide open even if not at their very best.

Maybe it's true that the latest lenses for any format are better wide open than older lenses tended to be, if not actually at their sharpest, to the point that they're now easily sharp enough at their widest apertures.

[Rob Campbell]

I think that for non-pro folks outwith the landscape (usually!) and architectural disciplines, central crispness is generally key.

I'm rather fond of shoooting with little DOF yet, at the same time, I find that I invariably drop aperture from, say, f1.8 to f2 out of some residual doubts about wide open performance. It's probably largely irrational, but that's how it goes, chez moi.

There's little doubt in my mind that images with a shallow DOF are often a lot more interesting, if only because the subject is forcefully present for all to see. On the other hand, and bad metaphors aside, with massive DOF I am reminded of trying to hold a conversation in a busy Spanish restaurant that's full of diners, all trying to make themselve heard. Confusion reigns even across the table. Or maybe my dining companions are all as ancient as am I, and convinced we have no need for hearing aids.

Rob

[Kenneth Tanaka]

The optical characteristics of a single lens remain interesting and noteworthy but are becoming less critical with each photographic generation. The lens usually had nearly the last, and loudest, word before an image was recorded during photography’s chemical era. Correcting for optical aberrations and deficiencies was difficult, requiring special expertise, equipment, and opportunities that few snappers possessed.

Today’s lenses are generally significantly optically superior to those from even a generation ago, thanks largely to computer-assisted design and improvements in materials sciences, coatings, and manufacturing. Even my least-expensive current-era lens renders a much cleaner, crisper image at any aperture than its chemical-era ancestor. (Yes, I realize that some TOP readers may consider a 60+ year old lens to have more “character” but, well, now we’re into other psychological aspects of imaging.)

More significantly, however, the lens has become just the first opinion of the digital image. Various electronic (re)mediations often take place before an image is recorded onto a memory card. Optical perfection is still, and will remain, very expensive and usually very heavy. But it’s also becoming increasingly unnecessary.

Looking in the not-very-distant future (actually already in the present) imaging will most often be the collaborative product of multiple lenses and sensors. Optical “perfection” becomes much more approachable if you limit what you need a lens to “see”. So having an array of specialist lenses continuously collaborating on images, via our ever-increasingly stupendous computing power, is the future of photography.

[Steve Jacob]

That '2 stops' thing is a myth. Almost any lens peaks between f/2.8 and f/5.6 in the centre (lower means better correction) because there is less spherical error.

So an f/2 lens typically doesn't require as much stopping down as an f/1.4 lens.

As with all measured values, whether it matters depends on the size of the image. Even then it will be affected by a bunch of other stuff, like sharpening, paper type, ink density, contrast...

It's quite possible to have a wonky lens that has 'personality' even if it's figures look iffy. Depends whether we value contrast and bokeh over sharpness and detail.

With smaller prints, these things often have more immediate impact. Resolution only really becomes a factor when we make large prints, whereas creative blur needs to be exaggerated somewhat in a small print because the background inevitably looks busier.

[PDLanum]

I have read many accounts of how "bad" fast lenses are when shot wide open. However, I also notice that the people complaining about "softness" refer to the corners where they habitually apply vignette's. Go figure, it reminds me of my friend who shot Canon back in the 70's while I shot Fujica. He bragged about how his Canon lenses outshot my Fujinon's as he proceeded to put on UV filters so he could smear Vaseline on them for that "dreamy out of focus look".
Just why does everyone these days feel the need to shoot in absolute darkness?

[James]

Hi Mike,
I have been using the Panasonic 20mm f1.7 on GX7 set to monochrome plus raw for my OC OL OY This morphed into OC, OL, 2.5Y, NC (No Color), AO (Arms Outstretched) NE (No editing), to match my iPhone technique and make it more focused ;-) Sorry!
Downloading into Apple Photos prevented me from seeing any of the shots in color or noting any of the settings.
During the first year I used only ISO 200 and f2.8
When not really taking pics, I tried a couple of variations to ISO and aperture just to see what they did. f1.7 is not so good anywhere other than center frame. f2.8 is perfect for people shots with great falloff.
ISO 400 is OK at 8 x 10.

10 days ago I loaded a lot of shots into Lightroom to check settings and histograms.
Of course, Lightroom automatically opened the raws and I was not happy with a lot of the shots when they were displayed in color.
In fact some were just not good at all in color.
One other interesting thing I noted from the metadata - the kit lens had never been on the camera.
The 20mm is one fine lens and looks to me to be about f4 or f5.6 eq when set at f2.8 - but that eq is dependent on subject distance.

Still use my "big guys" for real shoots, Yellowstone in winter minus 20F degrees etc., but I have the GX7 as my daily camera.

[Jim]

There are plenty of diffraction limited lenses, if you know where to look. For example all the Apo El Nikkors, the Ultra Micro Nikkors, and the RZ67 APO lenses are all diffraction limited wide open. most if not all of those have yet to be equalled in their respective areas, by anything made today. Today's lensmakers are too reliant on the crutch of post processing and software to correct for their abberations.