What's a 'Fast Lens'?

There's been some talk about whether this or that lens is "fast" or not since the DP1 came out sporting an ƒ/4 fixed lens. How "fast" is the Olympus E-P1 lens, really?

The concept of "lens speed" (referring to maximum aperture) has been variable over the years. Without launching into a history lesson, it's all been relative—Tessar-type designs are limited to fairly small apertures, for example, and first reaching ƒ/2.8 with a Tessar-type was an achievement. Generally speaking, though, lens speed was a prestige camera feature in the middle third of the 20th century, more or less, and cameramakers competed to see which could out-do the next. The market rewarded this tendency until ƒ/1.4 became common in normal lenses (the further from "normal" a focal-length is, generally, the harder it becomes to make the lens a fast one). Several cameramakers reached further than that, most notably with Walter Mandler's famous Leitz Noctilux, and several makers, Canon in particular, reached ƒ/1.4 with some fairly wide lenses for 35mm. The other famous fast lens early on was the 85mm ƒ/1.4 Zeiss Planar, which has long and interesting history that continues right down to the present day, in a fine lens released very recently. But the market as a whole didn't much care—ƒ/1.4 at the normal focal length turned out to be the point of sufficiency for most photographers where lens speed was concerned. Options that do better than that have sporadically been available, but have never achieved much in the way of popularity.

Of course, film speed has to be factored into that. During the only two stretches of time that I used Leica rangefinders—the first time for a period of about two years in '91–'93, the second time for something closer to a single year around '96 or thereabouts—I used Summicrons. (Leica, unique among cameramakers, names its lenses according to the lenses' maximum aperture; all the "Summicrons" are ƒ/2 lenses.) I was shooting Tri-X, rating it at E.I. 200. Also—somewhat oddly in retrospect—I never used either of those Summicrons at ƒ/2! The first main lens I used was a fourth-version (now called the "pre-ASPH") 35mm Summicron (which I once rather infamously dubbed "the King of Bokeh"), and the second time I used a custom-coated collapsible 7-element 50mm Summicron from the early 1950s. Neither lens was much good wide open, so I avoided the open aperture (and, for the most part, one stop down as well, if I could).

One might well ask, why use a Summicron if you're not going to use the lens wide open? It's a good question, especially since, on a Leica, you don't need to use the lens to see in the viewfinder. That, of course, was the other driver of lens speed: SLRs caught fire in the market starting in the 1960s, and, when you look through an SLR, you're looking through the lens you have mounted on the camera, generally at its wide-open aperture. The slower the lens, the dimmer the view. And why is that important? For focusing, of course. Photographers who have come of age since 1985 or so are probably aware that everybody used to focus manually, but only if you experienced being dependent on it can you really appreciate how important it was to have a good, snappy groundglass and a crisply fast lens to see through. On SLRs, you might never shoot at ƒ/1.4 with an ƒ/1.4 lens, but that maximum aperture was still very important nonetheless.

Zander at age 1, a much-loved family snap taken with a very fine fast lens, the OM Zuiko 100mm ƒ/2, wide open (can you see the telltale of slight spherical aberration?). This was a true candid; my uncle had just plopped his own hat on Z, and Zander responded by looking up at him and smiling. I got off one shot before my uncle took his hat back.

The increasing popularity of zoom lenses in the 1980s and '90s changed the equation again. Very broadly speaking, zooms are two stops slower than equivalent primes; if a premium normal prime lens is ƒ/1.4, a premium normal zoom is ƒ/2.8; cheaper, smaller lenses in each case might be one or two stops slower than that. This was really only practicable because of the parallel advent of autofocus. Slow zooms, especially mated to cheap finders, would have been very difficult to focus manually.

Nowadays, of course, another factor has once again changed the meaning of lens speed is the high-ISO capability of digital cameras. I distinctly remember the brief juncture at the beginning of the 2000s when digital image quality became good enough to tempt serious photographers, but the "speed" (we call it ISO, even though it strictly isn't) of sensors didn't yet match that of film. That changed quickly. Image quality still declines with increasing ISOs, but the general consensus is that every sensor/firmware package has a fairly well defined limit of "usable" image quality—and, with larger sensors, the number is usually amazingly high when you compare it to similar limits applied to film. My personal standard is that if a DSLR has good quality at ISO 800 and usable quality at ISO 1600, I'm happy. My current DSLR does considerably better even than that.

Image stabilization yields yet another twist to the story. IS is a "tripod replacement," not a "film-speed replacement," and that does have implications for how it's useful and how it's used. Even so, one or two stops' worth of further flexibility in low light or with long teles is often quite valuable.

The long and the short of it is this: in 1992 I was shooting with an M6 and Tri-X rated at E.I. 200, using an ƒ/2 lens that had poor image quality wide open, meaning that I avoided shooting wide open. The new Olympus E-P1 that we've been discussing for several days here has an ƒ/2.8 normal lens. But it probably also has "good as Tri-X" image quality at ISOs up to 800 or so, and its built-in image stabilization probably yields one or two stops' worth of shutter speed into "tripod territory." Let's say for the sake of argument that the newer lens design is also acceptable in terms of image quality wide open (even though that still remains to be seen). What that means is that, even according to these fairly conservative calculations, that I gain two stops in exposure index ("film speed") (ISO 200 to 800) and up to two stops in shutter speed (thanks to IS) using the two lenses at the same effective widest aperture (ƒ/2.8). And you're not dependent on the lens for the brightness of a TTL (through-the-lens) optical viewfinding image.

Or, put it this way: given the presence of all these conditions, ƒ/2.8 is the new ƒ/2.

You can say "more speed is never bad," but in practice, the market will eventually decide on a point of sufficiency, just like it does with all technical parameters in which various makers compete to satisfy real demand. The "point of sufficiency" is where most people decline to pay for further improvement (or buy it only for status). We might already have reached that point with megapixels and sensor speed, with 24 and usable 6400 respectively in the most advanced devices. (Only time will tell. The manufacturers will overshoot the point of sufficiency, but as they do, fewer people will pay for the increased performance.) However, for a small personal snapshot camera designed to be handy and portable—given that it has a large sensor with good high-ISO performance and IS—an ƒ/2.8 lens seems fast to me.

Mike

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P.S. Comment: "But I'm not so concerned about exposure, I'm concerned about achieving limited depth of field to isolate subjects."

Not picking on the person who wrote these particular words (or any individual who might have written similar words) personally...but this is total internet hooey. It's something the "thousand monkeys in a room" on the internet have convinced themselves is an issue. It isn't. Or it shouldn't be, to any pictorial photographer shooting pictorial subjects.

In this particular case: a) you don't use a 35mm-e on anything to "isolate subjects"; and b) the difference between ƒ/2 and ƒ/2.8 for "isolating subjects" is very slight, marginal at best; and c) isolating subjects has much more to do with how you use the lens than with a one-stop difference in aperture on that lens. Finally, d) most people who consider themselves "concerned" with "isolating subjects" just as often don't have enough depth of field as too much. I see the evidence all the time, in pictures, all over the place, everywhere. Here's just one (a sample from the E-P1 and 17mm lens). Just one of millions...do you see that this photograph doesn't have enough depth of field for the subject? (The only reason I can pick on this picture is that it's a sample of the new lens wide open, and is not presented as something that's aesthetically intentional. I try not to pick on actual pictorial pictures by actual amateur photographers who might be hurt or offended by having themselves used as an example of what not to do.) O, if I could but count the number of out-of-focus dog's noses I've seen because the earnest but hapless photographer was trying to blur the background....

The problem in photography from 1840 until about 2005 with rare exceptions (fashion photographers and their once-fashionable 300mm ƒ/2.8s come to mind) was to get enough depth of field. The problem was almost never too much. And then came the theoreticians of the shared armchair and their picayune calculations of sensor size and diffraction and all else that's much talked of in numberless fora but wrong....

Best advice: unless you're doing technical work, and have extremely strict conditions and/or requirements to deal with, and you thoroughly understand the issues from a practical as well as a (real) technical standpoint, then ignore everything you come across on this subject. Most of what's out there is 99.75% complete chrome-plated bulldung. (And as you can see, the persistence of the error—and the knowledge that it's never, ever going to go away—makes Mike a mite testy.)  —Mike

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Comments

[photogdave]

Hmmm...I didn't see any reference to depth of field.
Also, I wouldn't say the Summicron has "poor" image quality wide open. I wouldn't shoot a landscape at F/2 with it, but it's far from poor!

[Paul McEvoy]

I don't know Mike. I appreciate what you are saying. But I think we've come to accept more because we are trying to do more. I spend a lot of time in bars, shooting musicians in really terrible light, trying to make the best of it that I can. Sometimes I use flash, and I like that light, but I'll take whatever I can get in terms of ISO and lens speed. I won't apologize for it, either. The first night I had my 5D I went out and shot with the 50mm 1.4 EOS between 1.4 and 2 at ISO 3200 at a little rock show locally. I was hooked. But a lot of those pictures didn't look that great as prints. The ISO 3200 was pretty noisy (obviously, now that I think about it).

Anyway, if that lens was 2.8, and I had to shoot at 4, I wouldn't have been able to take those pictures. This is something I could do because the lenses were maxed out for film, and the sensors have developed significantly from film. Now that the sensors are getting even better, to make the lenses worse...that seems like a step sideways. I'd like the best lenses we can have, and the best sensors, thank you.

[tom]

But I don't care about speed, I care about depth of field to isolate subjects. And seen as with smaller sensors the DoF increases....

I want my 16-500mm F1.2 zoom :(

[WeeDram]

Mike:

Over on RFF I made exactly (nearly) that statement: f2.8 is the new f1.8. BUT ... for me it is not just about the ability to make the exposure at a certain ISO (er, it's ASA, dammit!), rather it is also about DOF. When you factor in a sensor smaller than 35mm film and the lens's extended DOF due to the shorter focal length, then lens speed is important for a different reason.

[Douglas Urner]

While better sensors are indeed changing the meaning of "fast" when we're talking about light gathering ability, there is still depth of field to consider. There large apertures rule, especially on small sensors where DoF is already limited. IMHO.

[Oleg Volk]

Wouldn't the sensor gain while viewing also depend on the lens speed? An EVF with f2.8 lens would be noisier than EVF with f2 lens.

[Julian Love]

Very good post Mike - sometimes we seem to forget how far we've come. Let's also not forget that an f/2 or f/1.4 lens on the E-P1 would most likely be rather larger too, somewhat defeating the purpose of a serious compact.

[Pat Trent]

Technicalities aside, to my mind the phrase "fast lens" implies the range from f/1 to f/2 inclusive.

[Ed]

2.8 might be "the new 2" with respect to the factors discussed; but there is one major exception to this analysis: bokeh and background blur. Both are much improved at f2 compared with f2.8, and, for this photographer, constitute a critical need which is not optimally addressed by the lenses currently available for the E-P1. This is particularly important if the optics require stopping down a stop or so for improved optical performance. For all of these reasons an f2 or f1.4 prime lens for the E-P1 would add greatly to its appeal and usability. If other photographers feel the same way please write and respond here; I think it is very important that Olympus know that this is something that photographers want. So in this sense, 2.8 is not the new f2, and can never be. The "pop" (accentuation of the subject in the foreground when this is the focus point) at f2 is just simply superior to that achieved at f2.8 with respect to the background. Let's hope that a faster lens quickly becomes available, such as the rumored 20mm f1.7; that would be sweet.

[john robison]

"...telltale of slight spherical aberration"

Just a guess, the hot spotting of the out of focus background highlights?

Fast lens? Guess I'm influenced by 35mm SLR's from the 70's so to me it's f2 or faster. That said, I really like compact lenses so for retrofocus wide primes I'll settle for f2.8 or even f4 on the really wide ones.

[Jared Lynem]

But 2.8 on a normal lens won't give you that delicious, isolating depth of field!

I hear there's never a dumb question, so I'll ask this one: does an ƒ/2.8 prime lens typically have a better t-stop than an ƒ/2.8 zoom lens? It seems to me in my biased prime-snobbery that this might be the case, but perhaps the difference is negligible.

[John Sarsgard]

Just a gentle reminder (we know you know!) that IS buys one or two stops of shutter speed for static subjects. It compensates for the moving photographer's hands, not the moving antelope! I'm still very much addicted to it on my Canon 5d. I do lots of things like wedding candids, and usually fire off a number of similar shots to get a good one where the subject(s) aren't moving when I'm at 1/15. In a church with no flash, IS still changes the game. If I had f2 available to me, I could trade off my subject movement challenge for a depth of field challenge. But IS is just the ticket for photographers who drink too much coffee.

[Ken Bennett]

Mike,

My current favorite lens is the Canon 35mm f/1.4, on the 1D Mark II body (which has a 1.3x conversion factor.) Shot wide open, of course -- why else carry it? I use it almost entirely for candid portraits, and it excels indoors and outdoors. Exceptionally sharp when I can nail the focus on the eye, then buttery smooth as it fades off to the corners. (I actually have no idea if the corners are ever sharp. Don't much care.)

Of course, it's impossible to manually focus wide open on a digital body. AF makes this lens usable for me, so thank the photo gods for that.

On the topic of the new Olympus digital Pen, I just got my old XA out of the closet. AFAIK it's the smallest full-frame 35mm rangefinder camera ever made. Great little 35mm f/2.8 lens, very sharp even at f/4, manual RF focus, aperture priority, etc. And it's smaller than my G-7. $10 worth of batteries got it working again, and $50 of film to feed it. I think it'll be fun to shoot for a while. (And my wife saw me spend the $60, and commented on the film expense. So I pointed out that a new G-10 would only cost about fifty rolls of film. Heh heh.)

So let me put in my request to Olympus: how about a Digital XA. m4/3 sensor, 17mm f/2.8 lens, manual RF focus, clamshell design. You can build up the interest online the same way you did with the Pen. I'd buy one in a New York minute.

[juze]

Quite.

I'm an extreme case. I shoot concerts in a badly lit bar (well, the concerts are amazing), and fast lenses don't really cut it. I need a relatively small aperture (f/2.8-f/4) to get an acceptable depth of field, and unless I'm going for intentional motion blur, I need at least 1/30 shutter time, although with the livelier bands, 1/125 would come in handy.

(By the way, my usual settings are ISO 3200, f/2.8, 1/30 to get a shot that is only one or two stops underexposed.)

Which is why I want, nay, need fast sensors. IS doesn't help. Fast lenses don't help. ISO does.

While I would love to have a nice 1.4 lens (I use Olympus, so I'm a bit limited in this regard), it wouldn't come in all too handy. I used to shoot Canon, and I'd have to stop the 85/1.8 down to 2.8 to make sure I could get enough DoF. Defeats the purpose, really, doesn't it?

Of course, there's the whole lot of minimum-DOF fetishists, and they love their fast lenses.

But for me, f/2.8 is quite enough.

[Robin P]

But doesn't that wide open ƒ/2.8 lens on a 4/3 sensor have the depth of field of a ƒ/5.6 lens on 35mm?
MF cameras rarely need lenses faster than ƒ/2.8 because with the bigger "sensor" that is sufficient for the required selective focus.
So, if you want that very selective focus and a blurred background then smaller sensor digicams are not the right tool for the job - unless you want to cheat and blur the background in software.
Just my 2 cents (as they say on the internet).

Cheers, Robin

[k4kafka]

Well it certainly is a cute little camera. But the jury is out as to the quality of the images it can produce,...which is, as you say...the real point (and shoot) of any camera.

[Clayton Lofgren]

So your current DSLR is the A700.

[paugie]

The last time I used a lens with a 1.4 maximum aperture was on a borrowed Minolta SR7 in 1967.
In 1985 when I had my Nikon FE2, my prized lens was a 35-70/3.5. Dunno, even back then, it seemed fashionable to get a zoom rather than a fast 50mm prime.
Now, with a Pentax K100D, my best lens is Sigma 24-60/2.8. Of course the Pentax-A 35-105/3.5 is sharp, too. But these 55 year old eyes don't focus too well by themselves, never mind having to use a camera in between the looked-at and the eyes.
I really wonder whether the market really chooses. It seems it was me choosing what was in the market - that which my pocket could afford.

[Mike Johnston]

Ed,
Let me put it this way. If you feel that way about it, then you'd be considering the wrong camera and lens to look at the E-P1 and its 17mm. Get yourself a full-frame camera and that 85mm f/1.4 Zeiss that I linked and you'll be a happy camper!

Mike

[Mike Johnston]

Obviously several people commented on the main text before I wrote that P.S. If any of you feel your comment has been retroactively ridiculed, let me know if you'd like it modified or removed. I didn't mean to "back-door" anybody (I think that's what they call it in gin rummy, right?) and if I did, I apologize. Sometimes things get caught in the switches....

Mike

[Ludovic]

That Zander candid is wonderful.

[Amin]

"Not picking on the person who wrote these particular words (or any individual who might have written similar words) personally...but this is total internet hooey."

I've read your comment describing this issue as "hooey" in the past, but a number of your own photographs shown on this site have utilized, to pleasing effect, more shallow DOF than will generally be possible with the Olympus 17/2.8.

Inability to control DOF has long been a knock on small sensor digital cameras. In terms of DOF control, the E-P1 with 17/2.8 sits nearly at the midpoint between a C-5050 and something like the XA or Mju II, to use all Olympus compact examples.* Whether that is enough DOF control for a given person is a subjective matter, but I don't think it ought to be dismissed as a non-issue.

Amin

*Based on shared armchair theory and a general personal impression derived from the frequent use of small sensor, Four Thirds, and 35mm cameras.

[Spiny Norman]

Re. your postscript: YES! (And I voice this agreement having spent the last decase with a 35/1.4 Summilux ASPH on my 35 mm camera probably 65% of the time; I, too, know well what such a lens can and cannot do.)

[Clayton Lofgren]

I don't even know Zander, but I love that snap.

[Ken Bennett]

MJ: "Obviously several people commented on the main text before I wrote that P.S. If any of you feel your comment has been retroactively ridiculed, let me know if you'd like it modified or removed."

I don't feel ridiculed, but I disagree with your DOF comments in the P.S. Photos in which the dog's nose is out of focus are perfectly fine -- I have many pictures of people in which only one eye is perfectly sharp. That's what I like, and I'm sticking to it.

[Mike Johnston]

Amin,
I'm not saying selective focus and d-o-f doesn't exist or that it can't be controlled for. Of course it does, and of course it should be. I just don't think there's a very clear *practical* understanding of which factors really matter and which don't. Large jumps--in sensor size, focal length, aperture settings--do of course make a difference in what effects you can achieve and how you have to achieve them. It's the reductio ad absurdum of assuming that every slight difference has a huge effect that I object to.

For starters, the theory projects the idea that the set of conditions is going to be unchanging. You then measure the tiny differences in achievable d-o-f and conclude that there's a real difference (which of course there is; it's just very small, is all). But in the real world--at least the real world of PICTORIAL photography, i.e., when you're out'n'about making pictures of the world--there are no set conditions. There is an infinity of possible pictures. So how do you sort them out? Well, you learn your lens and what it does, and you learn how to apply its technical abilities to the situations and conditions you encounter. It's immaterial in these real-world conditions whether your single-focal length lens is f/2 or f/2.8 (except that it's a stop of exposure control). You want more blur, just get in closer or find a background that farther away, that's all. you want less blur, step back or find a subject with less depth. There's not ONE daisy sitting in front of ONE background that has to be placed ONE way in the frame; there's an infinity of possibilities. At least when you're in the realm of minor, modest differences in your equipment, like one single aperture setting or a slight difference in sensor size, it's just not a technical problem. It's an artistic problem.

Mike

[Mike Johnston]

"That's what I like, and I'm sticking to it."

Ken,
That's fine too. [g]

Mike

[Amin]

Mike,

I agree with everything you just wrote. For practical purposes, one stop doesn't make much difference in the ability to make a photograph. For example, the E-P1 and 17/2.8 doesn't allow all that much more DOF control than a Sigma DP1. If one finds that aspect of the DP1 to be frustrating, this new Olympus kit is unlikely to change things. However, a couple of stops or a big change in sensor size can be significant, so someone who finds that aspect of a DP1 limiting may well have found a 17mm f/2 lens on the Olympus to fit the bill. Of course what one gives up is size and weight. Which compromise is best varies according to personal preference.

Consider what the second photo in your 'DMD' article would have looked like if taken with the EP-1 and 17/2.8. You captured a very nice moment with the young girl, and it's likely you'd have missed that moment by maneuvering for a better background or closer perspective with the EP-1. Sure that's just one photograph, but I often find myself in such circumstances.

I want the M-Zuiko 17/2.8 and E-P1 to work for me just as I wanted the ZD 25/2.8 and E-420 to work for me. The experience with the latter just has me a bit wary that the degree of DOF control with the former will make for a satisfactory experience in my case.

Amin

[John Camp]

My problem with this kind of discussion is that the issue is usually discussed in words, rather than in numbers -- but because I'm not a tech-head, I don't even know if it *can* be discussed in numbers (which I would prefer.)

What I know is, if I'm standing somewhat close to a person with an F1 Leica Noctilux on an M8 (a 1.3x sensor), focus on the eyes, and rock back on my heels, I lose the focus. It's that narrow.

I also know that with a Nikon D3 to shoot a Canaanite seal (the size of a dime, the thickness of an M&M) I've got to stop down my f/2.8 105 Micro Nikkor to around f11 to get enough DOF to be able to function effectively.

On the other hand using a small P&S I put my daughter in the middle of the the Champs-Élysées and both her face and the Arc de Triomphe some distance away were in fine focus. If I'd wanted to isolate on her face, I don't believe I could have.

So somewhere in the mix, speed of the lens/size of the sensor is important. Is there any resource that can give a quantitive value to these changes? Or, if a word-based description, something that tries to be more...uh...schematic in presentation?

[Mike Johnston]

"Is there any resource that can give a quantitive value to these changes?"

Sort of. There are what are called "depth of field tables" for individual lenses. These typically give depth of field plotted against distance settings for each aperture. Currently, the "Technical Data" PDFs at us.leica-camera.com provide these for at least some of the lenses (I didn't check them all), displayed as a series of bar graphs.

However, it's not that simple. (You realized this was coming, didn't you?) Technically, only image objects at the exact plane of focus are optimally sharp; as you move away from the plane of best focus, image objects get gradually less sharp. Theoretically, an imaged point will gradually become a blurred disk. The allowable degradation is known as the "circle of confusion." As long as the circle of confusion is acceptably small, the imaged object will either be indistinguishable from sharply-imaged objects in the plane of best focus, or so close to it that they will look acceptably sharp in the pictures. But here's the rub--the circle of confusion that you choose to accept as being affectively sharp is a judgement call. Thus, if you decide you're willing to relax your standards and accept a larger circle of confusion, d-o-f increases; be a stickler and set a smaller standard, and d-o-f decreases. So even a set of documents like the ones in Leica's PDFs are simply a judgement call, based on the standard of allowable blur they've decided to accept.

Not only that, but there are other complicating factors. In film photography,the coarseness of the grain of the film you're using matters, because grainier film resolves less. The less it resolves, the more of the unsharp areas will look the same as the sharp area, and the more APPARENT d-o-f you will have--without the LENS performance changing at all. Next, degree of enlargment matters too. Blurred objects that look sharp in small enlargements might no longer look sharp in large enlargements. Digital brings a whole 'nuther level of complication, because a Bayer array is not a direct report of the lens image--some of the "data" is extrapolated. Plus, you can "mimic" sharpness in certain ways in certain unsharp areas by using software.

Once you've quantified everything acceptably for one lens, you'll have to start all over again with another one. Any time you change cameras sensors, too, the d-o-f calculations for ALL your lenses might well change at once.

See why I recommend that people try to gain an intuitive, seat-of-the-pants VISUAL sense of d-o-f and not bother with numbers? You'd have to be a computer, or at least have a good dose of well-focused OCD, to cope with all the numerical information needed to even approximately describe the behavior of a set of lenses.

And we haven't even touched yet on psycho-visual factors, like the tendency of the mind to accept a bit more blur behind the plane of best focus than in front of it, and our tendency to accept less actual resolution in the presence of high-contrast boundaries (edges).

Why am I getting tired? [g]

Mike

[Mike Johnston]

N.b.: I had to shorten the previous comment to get it to post, so the explanation might not be ideally clear. So please don't quote me.

Mike

[Amin]

J.C.,

If you're used to how things are with your Nikon D3, in general a Four Thirds or Micro Four Thirds lens will give the same framing and DOF at half the focal length and half the f-number of the Nikon lens. All the things Mike mentioned will affect this, but it's a rough formula that has helped me, as someone used to shooting 35mm "full frame", to adjust and get the shots I want with Four Thirds.

I have an example of this using Canon and Olympus systems here: http://www.seriouscompacts.com/2008/06/bokeh-test-olympus-zd-25mm-f28-vs-canon.html

So, if using a 35mm lens only at f/5.6 and higher provides enough DOF control for your purposes on a D3, chances are very good that the Olympus 17/2.8 will likewise satisfy that requirement.

Amin

[James McDermott]

In those quirky olden times when we used to take photos, rather than talk about gear and bokeh, I don't recall anyone trashing the 'legendary' (sorry) Nikkor 105mm f2.5 for being sluggardly, yet my near-exact equivalent Pentax 70mm f2.4 has been laughed at for being just that. I've had no problems with it, nor my 21mm f3.2 (and I always focus manually). As for background blur, and isolating my subject, the 70mm's perfectly fine (no 21mm, no matter how fast, could be). I try for a subtle effect, mind you, not the other-worldly dislocation favoured by the tunnel-visioned.

[Patrick]

Regarding fast lenses, I had always thought this as well: the maximum sharpness of a lens will be at the aperture which is exactly at the midpoint of the lens's whole aperture range. Therefore, shooting at F8, for instance, with a F1.4 lens would be sharper than shooting at F8 with a F2.8 lens. So, even if one never shot at the maximum aperture, it was still advantageous for the sharpness of the lens as a whole to have the "fast" lens. Is this still true?

[CMS]

What's a 'Fast Lens'?

We are all looking at the maximum aperture. It might also be interesting to look at the the best (e.g. sharpest) aperture and to see how fast the lens is at that aperture. For years we were used to stop down quite a lot to get to that best aperture. Ironically, the faster the lens the more you had to stop down to get to that best aperture (e.g. f/1.4 lenses giving great results around f/8).

It seems to me that digital changed this. An increasing number of lenses are now calculated to give their best at larger apertures, sometimes even at the maximum one. This added to the higher ISO capabilities of digital cameras greatly reduces the need for fast apertures lenses.

Much in the appreciation of the 17/2.8 lens will depend on the aperture at which it is best.

[Cliff Lee]

After using faster lenses I've wanted f2.8 to have more depth of field than it does, but I have been limited to that to keep the shutter speed at a usable level. Generally I prefer more dof, to the point I prefer using my f31 fuji at f2.8 and iso 800 to take photos of available light photos of groups of people. Too many people ending up not sharp on the Dslr.

I'm excited by the 2x effect of the four thirds sensor, besides, if I need to keep a dogs nose sharp while throwing the rest of the face out of focus, I'll use my 50mm voigtlander nokton wide open. On this lens I've discovered how sharp it is at 1.5 and how little I manage to get in focus...

[Derek]

John,

Bob Atkins wrote an article over at photo.net a few years ago that deals with depth-of-field in a semiquantitative way. It's much more complete than a simple DOF table, putting some numbers to the concepts Mike mentions, so perhaps it's what you want. Note that the article's examples deal with Canon's cropped sensors, but you can obviously extrapolate it to other sensor sizes.

Personally, I'd like to see an f/2 lens for more light-gathering ability. With the extra DOF afforded by the smaller sensor, you can probably still get acceptable DOF even wide open in many situations. Of course, I'm working on a year with Leica, so I'm mercifully removed from the gear acquisition race for a while.... :)

cheers,
Derek

[robert]

I can think of another reason why I prefer faster lenses-it's because it tends to work out that they achieve maximum sharpness two stops down...

like your cron 35, a little glowy wide open, I bet was great at 5.6.

the canon 50 1.4 is absolute crap wide open, starting to look good even at f2, very nice across most of the field at 2.8.

which makes me wonder about this oly 17 2.8- what if it is crap wide open? or has such curvature of field that really only the center is sharp and the corners are very soft? then you are limited in your framing decisions.

in which case I would say all that other stuff, the IS, the high ISO is a little bit of "hooey".

the pannyleica lx3dlux4 is f2-haven't shot with it, but it might be that it is great at 2.8. In which case you have gained something by spec'ing a "fast" lens. F2 for the hail mary and great performance at 2.8.

just another way to look at it.

[Spiny Norman]

I spent about an hour last night going through the retrospective volume of photos by Helen Levitt. One thing that jumped out at me was what a very high fraction of the pictures would have been destroyed by shallower DOF. Same goes for Raghubir Singh -- a hallmark of his work is depth of field, and something wonderful is almost always happening in the foreground or the background or both. He almost never uses selective focus. Same goes for Cartier-Bresson.

For this sort of photography a camera like the E-P1 with the accessory finder mounted has great potential. We will see how that potential can be exploited in the field when we actually have had the camera for a while.

Robert Frank and -- especially --Bill Allard use selective focus more often, but they both spend a huge fraction of their time in really marginal light. Allard in particular is renowned for shooting wide open. But let's face it: this is not the sort of work a camera like the E-P1 is cut out for. It *is* the reason-to-be for cameras like the K-7 (if you want IS on your small primes) or the D700 (for pure sensitivity).

The funny thing is that you can have the whole E-P1 setup with 17 mm lens and accessory finder for about a thousand bucks (list! new! at early-adopter pricing!). To me, that's simply astonishing. Compare to the new Nikon or Pentax 50/1.4 lenses -- both ~$600 -- or to nearly any lens that has "Summilux" written on it.

[Mike Johnston]

"Regarding fast lenses, I had always thought this as well: the maximum sharpness of a lens will be at the aperture which is exactly at the midpoint of the lens's whole aperture range."

Patrick,
I don't know where you heard this, but it's wrong. The sharpest aperture of any lens is its sharpest aperture, and what aperture that will be depends on the lens. But it also depends on how you're defining "sharpness" and whether there are other factors that impinge. For instance, are you looking at center sharpness only or can you accept less sharpness in the center for more sharpness in the corners? What if the aperture with the best center sharpness also has a lot of falloff? Etc.

Sometimes rules of thumb that are technically "wrong" can be useful anyway, but I'm afraid this one is both wrong and also not useful, at least not as far as I can see.

Mike

[ctein]

Dear Mike et.al.,

I hesitate to jump in, because achieving LESS depth of field really is a minor issue. (I do not mean that in a personal nor subjective way. It is as Mike, said: only a very small minority of photographs/photographers benefit from less depth of field. Vastly more benefit from as much or more DoF. That's observable fact.)

Still...

Mike, you left out a very important confounding factor in all these armchair discussions-- boke!

It's like this: First, the real difference in DoF with a one-stop aperture change truly is subtle. Not entirely ignorable, but it's quite modest (much like a half-stop exposure change is modest).

Second, the issue here is not DoF, it's the need for some photographs (-ers) to keep the unimportant parts of the photo from taking your attention away from the important parts. That's all about suppressing high spatial frequencies; that's what distracts the eye.

It doesn't matter where those frequencies come from: it they're there, they distract (e.g., artifacts in a very high-compression JPEG).

The boke characteristics of a lens *radically* change that high frequency power spectrum. The difference in high frequency strength between 'harsh boke' and 'smooth boke'is much bigger than the difference introduced by 1, or even 2, aperture changes.

A lens with really 'jangly' out of focus rendition is going to produce more distracting backgrounds at f/2 than a 'smooth' lens will at f/5.6. Yes, the f/2 lens will have much shallower DoF... but that shallow DoF will not translate into the visual effect that's desired!

Declaring that some hypothetical f/2 lens will give you better DoF control (in the way that MATTERS) than an f/2.8 lens, absent any knowledge of the real imaging characteristics of the lens, is concentrating on the chihuahua and ignoring the mastiff.

pax / Ctein

[Bonaldi]

Am surprised there was no mention of dof at all in the original post. You're correct when you say that all the other changing factors have combined to make slower apertures less relevant to those interested purely in achievable exposures in poorer light, but that's almost such a truism that nobody who cares about the speed of a lens these days is doing so for those reasons -- they're doing it for the dof.

I agree that it doesn't matter as much with a 35mm-e lens as it would on an 85mm, but it still matters. In the flower example you linked to, I think it can be used an argument either way: there's slightly too much dof for me, so the eye is trying to resolve the not-blurred-enough-objects is in the background.

It's also slightly unfair to pick an f2, say there's little dof difference, and rule it out as hooey. There's a much larger difference between f2.8 and f1.4, and that's what some people will be comparing against. In my case, I'm hoping ultimately for a portrait lens that reaches that sort of speed. The Canon 85mm f1.2 is one of my all-time favourites, however, so I'll admit to being an outlier on this.

[Johnny R]

So lens speed is overrated you say? I think the opposite is true.

Here are some hundred random shots from flickr utilising a 1.2 aperture and I like what I see. If you do not, thats fine, but please dont try to tell us the 17mm Olympus does get anyhwere close...

Flickr Slideshow:
http://tinyurl.com/lgs5kw

[Nicolas]

You can say "more speed is never bad," but [...]

OMG, but fast lenses DO hurt!
They hurt my wallet first, and then my back and my wrist because they're too heavy ; and they hurt too because they are more susceptible of focus error.
Did someone already mention they hurt also because most of the time, they don't give enough depth of field and you have to stop them down?

[Andreas]

You can argue in circles, but what Amin often mentioned holds true (as also shown in his Canon Olympus comparison): 2.8 on 4/3 is 5.6 on fullframe, period. So in terms of blurred background, 2.8 is rather slow on 4/3, assuming that 35mm film is a floor limit to the ability of blurring backgrounds (not isolating subjects, which is a somehow silly term anyway).

I can understand that the endless discussion of differences between 4/3 and APS-C are annoying, because there are no differences artistically as you point out. Nonetheless, 4/3 should be faster to allow for easier blurred backgrounds. They promised small _and_ fast lenses, yet they only deliver 5.6 lenses in terms of dof.

Some confusion also comes from mixing up if something is outside dof or something is blurred "enough". Even with 4/3 and a 17 2.8 and focus at 3 meters not everything will be in sharp focus, but nothing will look like a nicely blurred background.

Another thing: with fullframe you get lenses like 35 1.4 or even 24 1.4 (now Canon and Film-Leica). With 4/3 you get 35-equiv 35mm 5.6. This is a difference of 4 stops, dof-wise.

So I agree that in terms of sensitivity to light 4/3 is fast enough, but in terms of allowing a nicely blurred background with moderate wideangle, 4/3 is way too slow, namely the equivalent of 2-4 stops.

[Roger Bradbury]

Before I bought a digital SLR I thought long and hard about maximum apertures. I had a Minolta X700, 50mm f/1.4, 35mm f/1.8, 24mm f/2.5. I used them wide open almost as much as any other aperture.
I bought a Pentax K20, and a 16-50mm f/2.8.
Today, Sunday, I took some photos in bright sunlight. Makes no difference what the maximum aperture was.
This evening I used the camera indoors. ISO 3200 and custom white balance, and away I go. Using f/2.8.
Not sure if there was ever a colour slide film that fast, but I would have lost more than a stop with a colour conversion filter, if I had one. I would like to have stopped down a bit for more depth of field.
What I do miss is depth of field scales on the lenses. I used to use them a lot. It can't be that hard to do.
At least Pentax put them on some (all?) of their primes.

[Amin Sabet]

"I hesitate to jump in, because achieving LESS depth of field really is a minor issue. (I do not mean that in a personal nor subjective way. It is as Mike, said: only a very small minority of photographs/photographers benefit from less depth of field. Vastly more benefit from as much or more DoF. That's observable fact.)"

An observable fact for the majority of photography history. However, for those of us using 35mm and smaller format cameras with modern digital sensors (perhaps most of us fall into this category?), the problem of needing more DOF is far less of an issue than it has ever previously been. This too is an observable fact. Whether too much DOF has overtaken too little as a creative barrier for most digital photographers, I am not certain, but I wouldn't be surprised if it had.

[Spiny Norman]

Some facts might help here.

At B&H, the Canon 24/1.4 is $1700; it is 94 mm in diameter and weighs 650 g. The 35/1.4 is $1250; it is 78 mm in diameter and weighs 580 g.

The newish 24 mm Summilux is smaller, of course. It is still heavy at 500 g, and it costs $6000. The 35 'lux ASPH (my favorite lens for the last decade) is remarkably compact and lighter, at only half a pound, but it still costs $4100.

Again: an E-P1 body *and* the 17/2.8 *and* the optical finder is $899 at B&H. I don't know what the lens weighs but the body is 335 g. And can do something that NONE of the lenses listed above can: IS.

Of course, if you *really* need to run that $6k 24/1.4 Summilux on an E-P1, Panasonic will happily sell you a Leica-authorized µ4/3-to-M adaptor.

One last thought (a repeat of an earlier pointer by MJ): everything is wonderful, yet no one is happy.

http://www.youtube.com/watch?v=jETv3NURwLc

[Ade]

Johnny R: I'm not rising to the rest of your post, but that slideshow is rather good for a set of "random" images. Thanks for the link.

[Keith Lommel]

"At B&H, the Canon 24/1.4 is $1700; it is 94 mm in diameter and weighs 650 g. The 35/1.4 is $1250; it is 78 mm in diameter and weighs 580 g."

True, but a Canon 35/2 can be had for $300 and only weighs 210g.

Voigtlander makes a full-frame 35/1.4 weighing just 200g ($530), and a 175g(!) 40/1.4 for just $380.

[Luke]

Just curious: How old is Zander now, and how does HE feel about that photo??

[NerdieMcSweatervest]

Ctein says

[O]nly a very small minority of photographs/photographers benefit from less depth of field. Vastly more benefit from as much or more DoF. That's observable fact.

Ain't that the truth. Anybody bought a cookbook published in the last few years? What's with the extremely narrow DoF of nearly every photo? I don't know about you, but I like to actually see the illustration -- all of it -- of the recipe.

[George C]

I agree with much of what you have to say Mike, but on the issue of 'you don't use a 35mm-e on anything to "isolate subjects"' I think you're a little quick: it can be done and it is done well by some people. I'd refer you to a couple of photos by a young Londoner who gets by rather well with his 35mm f1.4:

http://www.flickr.com/photos/iwasharry/2555202785/in/set-72157605559072574/

http://www.flickr.com/photos/iwasharry/2670115530/in/set-72157605559072574/

Nevertheless you remain a veridical voice amongst the throng of internet rubbish out there, keep it up.

[Mike Johnston]

"Just curious: How old is Zander now, and how does HE feel about that photo??"

Luke,
He's 16, and he "doesn't care." I didn't actually ask him, but he says that to pretty much everything. [g]

Mike

[Shawn]

Thank you for writing this entry, Mike. I know what you mean...

You get former newbies turned forum veterans passing on the fast lens mantra to other newbies. The classic (and most irritating) example thrown around on every camera forum:

"forget lens A, B, or C. Just get a 50/1.8... Best $100 you ever spent... DOF, bokeh, and low-light capability beyond your wildest dreams... I always keep one in my camera bag; it's so small and useful, you'd be a fool to leave it at home"

A couple posts down, someone chimes in: "yep, all HCB (or insert legendary photographer here) used was his trusty Leica and a 50 mm lens, and look at him now!"

... and so on and so forth.

[Paul W. Luscher]

I will have to disagree slightly with your comments about "F2.8 being the new F2." I have the Olympus F2 14-35 zoom lens (See? they can make an F2 zoom...), and that extra stop has come in handy in some of the shooting I've done.

Got pics of blues musicians shot wide open at ISO 2000 at between 1/60 & 1/30 ( I was kneeling at their feet), which gives you some idea of the "available darkness" conditions we are talking about. Not sure a 2.8 max lens would have helped much in those conditions....