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Saturday, 10 September 2011


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.

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

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).

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.


"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.


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?

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.


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.


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

rgds phil

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?

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.

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.

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.

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

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.

"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.

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 :-)

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.

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.

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.

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.

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?

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

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?

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.

"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.

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!

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

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.


"Mike replies: Only cool kids shoot Konica!"




...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!


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!

Here is a pretty good methodology for a lens check:


"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."

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.


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