Apertures Made Simple (Part II)

...Or, "Sometimes it's not so simple." :-)

The basic rule of thumb I put forth in Part I of this article—to use the three middle apertures to get the best optical quality from your lens, whatever that range happens to be for the particular format you choose to use—was one of the very first things I learned in photography. My father gave me a Konica Autoreflex T3 for my 16th birthday, and the T3 had shutter-priority AE—you set the shutter speed with the shutter-speed dial and the camera set the aperture itself according to its meter reading. The viewfinder featured an indicator needle protruding in from one side and a vertical row of apparently meaningless (to me) aperture numbers. I just didn't know where the needle ought to be. My father had a professional photographer friend, the late Arnie Gore, and Arnie told me to keep the needle in the middle—to make the needle fall on the eight, if possible, or one number on either side of it, except when the shutter speed got down below 1/30th. Useful advice for a novice like I was at the time. I followed it for years.

Of course, as you might know, there are situations when "use the middle apertures" isn't optimal advice.

The first, most compelling reason is if you're doing some sort of specialty work. Portraits seldom look best when the lens is well stopped down; you'll usually want to experiment with wider apertures for portraits. At the other extreme, macro work often requires smaller apertures because depth-of-field is related to subject distance—the closer you are to what you're photographing, the less depth-of-field there appears to be. So macro photographers often stop down more. These are just two examples. There are many more such situations.

Next in importance is when you'd seeking specific visual effects that you think a particular picture needs. Two examples might be shooting wide open to get lots of bokeh and characterful aberrations, or stopping down more to get more of a scene in focus front-to-back.

Those two things have a heavy degree of overlap, of course. When a fashion photographer routinely photographs models on 35mm or full-frame digital with a 300mm lens wide open, it qualifies as both a specialty application and as a desire for a certain "look."

But purely in optical terms, too, different lenses are different.

For one thing, slower lenses usually clean up faster than faster lenses, for a given focal length. A 50mm ƒ/2.8 macro lens might reach its optimum and be diffraction limited* one and a half stops down, whereas a 50mm ƒ/1.4 lens might not clean up adequately until you reach ƒ/5.6—four stops. Which puts the lie to the old rule that you should stop your lens down "two or three stops" for the best results. Usually that advice works—just not always.

Almost no lenses are "diffraction limited,"** per se, but I did use a Leica 90mm ƒ/2.8 M lens once that reached optimum performance one stop down. And it was very good wide open. A lens like that can effectively be used at any aperture, with different apertures preferred only on the basis of your desired depth of field.

Then there are those dogs that just suck at every aperture. Fortunately, those are becoming much more rare these days too, as computer-aided design has become the norm and quality control has become mostly a solved problem. To the extent that some lenses are still of poorer quality than the best ones, that property can be said to be partly "designed in"—usually, of course, in the pursuit of cheaper selling prices.

Lenses of radically different focal length will have different characteristics as regards the usability of various apertures.

Even the very best lenses are still a mass of compromise and limitation. One very highly corrected lens I used once—it was a 100mm Zeiss Hasselblad lens —had a decidedly pentagonal aperture shape and alarmingly poor bokeh. Out-of-focus foliage was a bizarre sea of bright pentagons! So much for perfection; there's really no such thing as a perfect lens. (Just maybe one that's perfect for you.)

Know your apertures
The best thing, of course, is to know your lenses. I've always advocated using as few lenses as you possibly can—four at most, two ideally, and one if you're hard-core. One reason is that the fewer lenses you use, the better you'll get to know them.

I do sypathize with zoom lens users, who have an exponentially tougher time getting to know their lenses, because they have two variables to contend with instead of just one. With fixed-focal-length lenses, which I prefer, all you have to do is learn how the lens behaves at each aperture. With a zoom, you have to learn each aperture at each focal length. No wonder many casual amateurs and occasional photographers never do learn what's going on.

How a lens performs wide open and where it reaches a practical optimum can be important considerations. One of the better lenses I ever used was the tiny Fujinon 60mm in the Fuji GF645s. Unfortunately, the full stop or widest aperture was useless because its optical quality was so poor at that aperture. It really needed to be closed down one stop—two was better—to be used. Because it was a slow ƒ/4 lens, this was a serious limitation. I ended up using that camera a lot on a tripod—which was somewhat conceptually dissonant, since the camera was a small, portable rangefinder. The lens sure was beautiful at ƒ/8 and ƒ/11, though.

Note, too, that when I say a lens is optically best at its middle aperture, I'm not just talking about the point where it reaches highest certer resolution. Remember what I said last time: "A lens image is always a balance of many properties. Always." So center resolution might be best at ƒ/4, but is falloff? Is corner sharpness? Is evenness across the field? That magic middle aperture is just where the best balance of all qualities occurs.

As ever, being ever the empiricist, I'd advise you to learn your lens by looking. Now that pixel-peeping on our monitors is so easy, it's not a lot of work to shoot some scenes "up and down the aperture range" and simply look at the results. Don't get anal about this or that property—the absolute resolution in the center of the field or the precise qualities of the bokeh. Just look at examples and see what you like and don't like, what's acceptable to you and what isn't. You'll eventually get a feel for where the problems are showing up visually, and thus you'll begin to know when you'll want to use certain apertures or avoid others.

I groused the other day about how all cameras seem to be getting "good enough" these days. (Only a dyed-in-the-wool gearhead could grouse about such a thing!) But no matter how good lenses get, a really fine lens can still justifiably be a photographer's prize possession. And a lens you know well is almost always finer than one you don't, when it comes down to pictures.

Mike

*The term denotes the point in the aperture range at which diffraction becomes the aberration that degrades the picture the most. At wider apertures, other aberrations predominate and overwhelm the smaller effects of diffraction.

**When the lens itself is said to be diffraction limited, it means it's diffraction limited when wide open. These lenses do exist, but they're very rare, especially among consumer lenses for pictorial photography.

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Original contents copyright 2011 by Michael C. Johnston and/or the bylined author. All Rights Reserved.

Featured Comment by marcin wuu: Speaking of Autoreflex—Mike, I think you might find this image to your liking (it's of my son, as of now age 7):

"(And, in reference one of your previous articles, it was shot with sony A850—the best digital 35mm camera, save the A900 ofcourse :))"

Mike replies: Only cool kids shoot Konica!

Comments

[Bob Rosinsky]

I had a weird thought last night/morning during a bout of insomnia. I started thinking about whether or not it makes sense to design a sensor that clusters more pixel wells in the center and fewer along the edges, where lenses tend to underperform. Or maybe, make the pixel wells at the edges bigger, so that they will have better light gathering properties. The human eye sort of works this way--high concentration of cones in the fovea and a higher amount of rods towards the periphery.

[David Zivic]

Thanks for these free aperture lessons Mike. I actually learned a lot.

[alan]

There's a few cases where focus shift makes the lenses less sharp at middle apertures especially at close focus distances. The leica 35mm summilux asph and the zeiss 50mm sonnar for m mount seem to be optimized for specific apertures (wide open typically).

[Patrick Perez]

Re: the Fuji 645 f/4 lens, you mention it only really worked well stopped down to f/8, and that was a problem, but didn't you also say f/8 was your preferred aperture in 35mm? And on a related issue, as format size goes up, handhold shutter speeds get longer for given enlargement, if I understand things correctly (no guarantee there!).

But this whole topic of knowing the optimum aperture for one's own lens makes me wonder if there is a camera where the photographer can set aperture and shutter and have the computer (I mean camera) shift the ISO for proper exposure? Seems like a killer feature for many shooting situations and easy to implement.

Patrick

[Mike Johnston]

"Re: the Fuji 645 f/4 lens, you mention it only really worked well stopped down to f/8, and that was a problem, but didn't you also say f/8 was your preferred aperture in 35mm?"

Well, yeah, but as Mick Jagger said, you can't always get what you want. In the film days, you couldn't shoot at f/8 all the time. The film I shot for years was ISO 80. The ability to open up to f/2 when necessary was a lot better than being restricted to f/5.6 no matter what.

Mike

[erlik]

When the lens itself is said to be diffraction limited, it means it's diffraction limited when wide open.

Mike, can you run that one by me again? If the diffraction strikes when you close the aperture down, what does it mean they are "diffraction limited when wide open"? Are you talking about the superteles with the brightest apertures of F8 or F11?

[Mike Johnston]

alan,
Focus shift doesn't make a lens less sharp at any given aperture. It only means it might not be focused at f/8 quite where it looked like it was at f/1.4 or whatever. This can be a problem, or it might not be--because small errors in focus are often covered up by d.o.f., and focusing systems are seldom terribly precise in the first place.

Mike

[Mike Johnston]

Vlatko,
No, the diffraction-limited stop is simply the aperture at which diffraction becomes the dominant aberration--think of it as the last aperture at which stopping down does any good.

As you stop down, other aberrations are gradually brought under control. Also as you stop down, diffraction slowly gets greater--it's negligible at wide apertures and a big problem at tiny apertures.

There are some lenses that are so highly corrected (stepper lenses, for instance, or satellite surveillance lenses) that that definition of the diffraction-limited stop is true of their widest aperture--in which case it's said to be a "diffraction-limited lens." That's all.

Bear in mind I'm not an expert on various esoteric lenses, because my interest is in pictures, and my interest in optics is secondary to that. In some cases I actually don't like "perfect" lenses as well as less perfect ones, because the latter can make better pictures. Technically, aberrations are not desirable, but pictorially, they sometimes are.

Mike

[phil]

@Patrick Perez.
Hi,
That's the TAv option (shutter and aperture priority)on Pentax (and maybe others).

rgds phil

[Dave]

I'm not a gearhead, I wish I could afford to be! I completely understand what you mean by this post, but isn't the best aperture the one for the moment you shooting on the lens you are shooting on? Outside of lab conditions, are the marginal flaws important? I follow the middle aperture philosophy most of the time, but if I am in a spot where those don't work I have no problem opening up or stopping down because in the end, if the photo is right no one will notice the little flaws.

Or am I a being foolish in my supposition?

[erlik]

Ah, got it. I think. :) Wasn't thinking about the corrections.

Patrick, Olympus has that auto-ISO-on-manual feature. It's limited by the auto ISO range, though. That is, when you set up the camera, you set auto ISO to be, I don't know, 200-1250 and then the camera chooses the ISO in that range afterwards. The possible values outside the set range are ignored.

I think Pentax has it, too. Or something similar.

[Ruby]

@Patrick:
Pentax offers the TAv setting. I set my aperture and my shutter speed, the camera sets the ISO. I can choose the upper limit I want it to use in the custom settings. I have my camera on this setting almost all the time, because my K5 handles the high ISOs really well.

[Kelvin]

I rarely get the opportunity to even consider 'optimum aperture' as a factor in my photography. I find that the lighting conditions dictate this, especially when I'm using film. Most of the interesting lighting situations I encounter are either fairly low light (in which case I either shoot wide open or use faster film, thus negating any resolution benefits of stopping down) or using artificial light (eg. studio, when I'm more interested in controlling depth of field). "Optimum resolution" is way down the list of aesthetic priorities in my shooting.

[ian]

the oldest photojournalist's rule in the book ( and the one taught to me, I might add) was "F8 and be there."

[JR]

The best optical quality is highly overrated, at least in the digital word. Since I went back to film, I find the imperfections at fast apertures far more interesting. F5.6 or F8 is just too boring. A great lens such as Pentax FA 31mm F1.8 is marvelous on film F2.8 or faster.

[Michael]

"But this whole topic of knowing the optimum aperture for one's own lens makes me wonder if there is a camera where the photographer can set aperture and shutter and have the computer (I mean camera) shift the ISO for proper exposure? Seems like a killer feature for many shooting situations and easy to implement."

Check out the Pentax K-5. It has a mode called "TAV" that does just this. I use it all of the time. I set the iso to auto adjust between 80 and 25,600. When noise starts to bloom in the higher iso ranges, a little pp with LR, plus Topaz DeNoise, or NIK Define takes care of things. I used to worry about keeping iso low to control noise, but now, no more.

[Nicolas]

In the getting-to-know-your-lens(es) department there are lots of variables. Close up vs far away, high contrast situations vs low contrast, focus accuracy, curvature of focal plane, distortions, aberrations, etc. Perhaps you could take us through the full list with your insights and thoughts on their relative importance in the real world :-)

[David Dyer-Bennet]

Nikon DSLRs can be set in manual exposure mode with auto iso set; at which point they use the aperture and shutter speed specified, and adjust the ISO for correct exposure. I find this useful sometimes in really bad light; I set the slowest conceivable shutter speed and set the lens wide open, and put up with whatever ISO results.

[Frank]

Everybody still uses the word 'stops'. There are no stops or stop-clicks on contemporary lenses anymore, no tactile feeling, no rings. Software deals with aperture. So I wished there was another word for 'stops', but no ... it has lost it's meaning in todays lenses.

[Crabby Umbo]

Plus One on the Fuji 60mm, a frustrating camera to use with incredible results when used 'correctly'...I used to shoot environmental style portraits of people with that 60mm, shut to f/8, and was always stunned by the results...too many weird little deficiencies, tho; I just traded in a Fuji 6X7 that I was doing street photography with, because I hated hand metering everything and trying to do it fast. Bought the Fuji 645 because it had an internal meter, but the meter was virtually impossible to use 'on-the-fly', hard to see, hard to set, baaa. Ended up selling the camera to someone who fell on it running for the bus, and smashed it to smithereens!

Guess what I needed was a Mamiya 7, but financially that is never going to happen!

When I look back on lens quality, tho, especially wide open, and slightly shut down, I had to go a long way before I surpassed the East German manufactured stuff I was using as a kid with my Praktica Super TL, for some reason, those lenses were just 'there', and better at more apertures than a lot of the Japanese stuff I went on to use.

[Chris Bertram]

So one thing I'm thinking as a result of reading these two posts, is that crop-sensor DSLRs may actually be a very good choice over full-frame ones. Not only are they typically lighter, but your best choices of aperture for normal photography allow for faster-shutter speeds and so are more hand-holding friendly too.

On an opposite sort of note, I'm also wondering what my "middle" choice should be for medium format (I have a Rollei) I'm guessing at f11.

[Roger Bradbury]

I did write a comment earlier in answer to Patrick; and like several others told him about the TAv mode. I suspect that I forgot to click on "post" because I can't see it here, but I might just be confused by the time zones. Either way, doh!

I wrote that several Pentax cameras had this feature, listing the K10D, K20D and the K7, but not the K5, because that's what it says on the Pentax UK website. Of course, this is wrong.

Perhaps I should check the Pentax UK website again in a week or two, to see if it's changed, and we will see then if any of them read TOP. : ]

On second thoughts, d'yer think if I contacted them direct I might get a K5 out of it?

[ctein]

Dear Frank,

May I offer a counterpoint argument?

One of my problems edcuating the new digiterati is that they have invented new terms and descriptions for well-established concepts. If words didn't already exist, it would be fine. But in using the new words, many of those people discard all the old knowledge usefully gleaned from film, because they don't even realize they're dealing with equivalent (or at least convertable) concepts.

Examples: "dynamic range" instead of "exposure range" and "lines" instead of "line pairs"

Coming up with yet a new term to replace "stop', simply because lenses don't have physical stops, would not better educate people about the craft of photography.

pax / Ctein

[Aaron]

Really?
It seems so very odd to me that we would get caught up in such a discussion.
I like the idea of the discussion of course. Very cerebral. How to wring the most performance possible out of a lens but doesn't the circumstance dictate the aperture used as much as the desire for optimal?
The thing that I come back to is that I'm amazed and typically incredibly pleased with the performance of so many of the manual focus primes I've shot over the years from Super Takumar thread mounts to Leica M. Either I lack the (thankfully) as yet undeveloped eye to notice a given lens' shortcomings OR the described shortcoming are really so much bluster as to be irrelevant apart from navel gazing discussions over coffee. No doubt entertaining but should we be out burning film insted?

[hugh crawford]

Crabby;
The first camera I paid for was a Praktica Super TL with the Pentacon née Meyer Oreston 1.8/50 lens in 1968. I had no idea how lucky I was to have picked that camera. It had a wonderful lens and the best part was that big stop down metering button on the front. It forced you to do a DOF preview every time made a meter reading, which taught me a lot. It eventually got stolen and I replaced it with a much more expensive camera and was disappointed that the quality was no better.

[hugh crawford]

Frank;
"Everybody still uses the word 'stops'. There are no stops or stop-clicks on contemporary lenses anymore"
They are called "stops" because they stop the light not because they click. They were called "stops" when photographers used waterhouse stops and you carried them around in your pocket. This gave photographers the opportunity to exclaim "I've got a hole in my pocket!", which seems to be a running gag among wet plate photographers, but as far as I know has not caught on with the lensbaby crowd.

[Brad Nichol]

As a summation I feel what Mike is originally trying to impart is that we will gain the best bang for the buck if we invest the time to really learn about our particular lens.

The approach of so many photographers is to buy a whole mass of lenses in search of optical nirvana and then never really achieve anything much photographically because they do not understand their optics well enough to capitalize on the strengths and weaknesses they present.

A while back to demonstrate the value of really knowing your lens to my students I undertook an extensive array of tests of the worst lens I own to see what performance could be wrung out of it...the lens was a 26 year old Minolta 28-85 zoom. In the end I shot around 1500 test images and determined optimal apertures for all focal lengths, field curvature characteristics, vignetting, chromatic aberrations and the corrections needed, flare issues, macro performance and much more. I joked with my students that I probably know more about that lens than anyone else on the planet....maybe I do.

The net result, since then I have used that lens more than any other lens I own, I use it's faults to effect and it's strengths as well. Ultimately over the past 12 months that cheap ( I paid $70.00 for it I think) has earnt me more money than any other lens I own!

The information on the lens filled about 80 pages in my last workshop manual and looking back at it, it still fascinates me that a supposedly dog of a lens can actually be a real stallion.

Indeed there is great power to be gained from really knowing your lens!

[ctein]

Dear Aaron,

I think that happens less often than one might imagine. About the only time you're limited to one and only one aperture is when the light level is so low that you have to work wide open to get even a minimally acceptable shutter speed.

I think that otherwise, you'll always have a range of choices.

What Mike is doing in these two columns is giving you a set of mental aim points for aperture-- where you'd like it to be, under typical conditions. The real world may prevent you from getting there, but it's still useful to know where they are when trying to decide which of the several usable aperture settings to choose.

pax / Ctein

[Patrick Perez]

Dang it! First Ctein, then Hugh jumped in with the correction I was going to offer Frank re: use of the word 'Stop'. Hugh even mentioned my trivia-worthy term waterhouse stop.

I especially agree w/ Ctein about new photographers inventing new words for old things. Sensels, indeed! I recall in high school 30 years ago proudly pre-empting my computer class teacher who proudly was explaining a new term he had just learned. I already knew the term pixel (origin: picture element). Fortunately, this occurred after school in the computer lab, not during class. I'm such a nerd.

Patrick

[Patrick Perez]

"Mike replies: Only cool kids shoot Konica!"

Nerd!!!!!

Patrick

[Crabby Umbo]

Hugh!

...you said it! Whenever I think of building a 'supercamera', it's amazing how many things I think of using from that old Super TL, especially, as you say, the big metering button on front of the camera, as well as the angled shutter release on the front of the camera (I don't think anything has ever been built that allows you to hold a camera steadier), and that weird film threading cage that always worked and threaded your film in an instant!

Ctein,

One of my base arguments against the mayhem and complication that is PhotoShop, is that it was never originally designed for and by photographers, and did not use photography terminology well. No 'stops' for light, no 'grades' for contrast, just an arbitrary scale in numbers, that didn't tell you if you were opening by a stop or flattening by a grade, which photographers had used, and understood forever, and which represented a 'known' amount in their minds. It has always been a pre-press program designed by software engineers, and just adopted by photographers.

Whenever my 'cross-discipline' friends talk to me about software (i.e. people that are 'stills' shooters as well as cinematographers), they always say how virtually all the great digital electronic editing programs use age-old film editing terminology, and virtually none of the programs for still work do, or even make as much sense!

[KeithB]

Here is a pretty good methodology for a lens check:

http://www.bobatkins.com/photography/technical/lens_sharpness.html

[Mike Johnston]

"The approach of so many photographers is to buy a whole mass of lenses in search of optical nirvana and then never really achieve anything much photographically because they do not understand their optics well enough to capitalize on the strengths and weaknesses they present."

Brad,
I mostly agree with your post except for the second clause in the quote above. It's very possible to achieve a great deal photographically without understanding lenses at all; many great photographers have done it. We need to remain mindful of the distinction between technical and artistic accomplishment. I have merely been talking about the former here.

Mike