[mohb]

Why does it seem to have become the Holy Grail of lens and/or camera performance? As most cameras and photographers struggle focusing with it and the extreme narrow DOF is a minority taste its importance seems overrated.

[Ari]

Two reasons - that very shallow depth of field is an effect some photographers like (for artistic reasons) and also, it means you will more than likely have a very sharp edge - to - edge coverage at a lower aperture. So f4-7 may be sharper on 1.4 lens than say on an f4 lens.

[pathdoc]

f/1.4 seems to represent a dividing line in fast lens design, beyond which point the best becomes the enemy of good enough. There are, for example, vast numbers of f/1.4 50mm and 55mm "normal" primes, but the number of f/1.2 primes (both absolute and in terms of number of lens designs) is far less. After that, things start getting more expensive because it's difficult to provide both a wider aperture (within the space available in the mount) and the appropriate optical design to ensure that lens performance at that wide aperture is usable. Take a look at the REAR element of 50mm lenses from f/2.0 to f/1.2 and you'll see just how critical the diameter issue is becoming.

Technically it should be possible to create a shorter focal length lens with a vastly wider aperture, if you go purely on the definition of the f/stop, and I've asked this question; turns out arranging the optics to provide a useful result becomes trickier and trickier, and the best anyone has usefully done with a highly specialised lens is f/0.8 or so.

It's not that f/1.4 is a holy grail - Canon has an f/1.0 lens and I believe Voigtlander has an f/0.9; it's that like the speed of sound back in the late forties and early fifties, there are important engineering and cost barriers in the way of going much faster.

[dtmateojr]

Why does it seem to have become the Holy Grail of lens and/or camera performance? As most cameras and photographers struggle focusing with it and the extreme narrow DOF is a minority taste its importance seems overrated.

It's not important to the photographer. It's important to the manufacturer. It's all about the money.

[Sandy Hancock]

Won't a brighter viewfinder image with shallow depth of field actually make critical focus more precise? I quite enjoy manually focussing my A50/1.2

Fast lenses are premium products - companies use better optical formulas and components for them. Usually that means they are well built and better corrected for aberrations.

Generally speaking, lenses are sharpest a couple of stops down from wide open, so an f/1.4 lens might be optimally sharp by f/2.8, while an f/2.8 lens might need to be stopped down to f/5.6. This helps with subject isolation for many types of photography.

If you want more depth of field you can still stop a fast lens right right down, but the converse is not true.

On the down side of course, they cost more and are bigger and heavier. The choice is up to the consumer.

[LensBeginner]

There's another perhaps secondary trade-off, but one that's worth considering if you're planning to do some low light, "bokeh" shots, which is the shape of OoF highlights.

for instance, the old SMC-M 50/1.7 (I'm talking about it merely because it's a lens I'm familiar with) exhibits round bokeh only wide open, at f/2 the bokeh becomes unpleasantly jagged (at f/2.8 it's hexagonal but at least it's not serrated!)
That's ok if you don't have prominent OoF light sources, but can be an issue sometimes.
Since I often stop it down to f/2 or f/2.8 for sharpness and DoF, that's something one has to be aware of, especially Ethan purchasing lenses which can be opened even more.

[dtmateojr]

the jagginess isn't caused by stopping down. It's due to the shape of the aperture blade. has got nothing to do with lens speed.

[Na Horuk]

minority taste its importance seems overrated.

It generally is overrated. The real reason why f1.4 lens is great is that you can shoot it at f2 and get great IQ. Whereas the same focal length lens of f2 will be "wide open" at f2, and wide open is generally not the best quality, so you would have to stop down that f2 lens to f4 or so. Of course, nobody will agree with the statements I just made, but that is the main advantage that I see.
f1.4 can also help with viewfinder brightness, but f2 or f1.8 is already pretty bright. It can help with focusing on some lenses, but it can actually be a hindrance with focusing on other lenses (like some notoriously difficult to focus 85mm f1.4 lenses)

Won't a brighter viewfinder image with shallow depth of field actually make critical focus more precise?

Even with a modern, small DSLR viewfinder, with focusing screen optimized for slow AF zoom lenses, not for fast MF primes? I can't agree.

for instance, the old SMC-M 50/1.7 (I'm talking about it merely because it's a lens I'm familiar with) exhibits round bokeh only wide open, at f/2 the bokeh becomes unpleasantly jagged (at f/2.8 it's hexagonal but at least it's not serrated!)

True. Though, if the lens has round aperture blades (as many modern lenses now do), this is minimized. This is mostly a problem of a certain era, where lenses no longer had 8+ aperture blades, but they were not yet rounded. So you end up with some lenses that exhibit jagged and hexagonal OoF highlights. The character of the bokeh and aperture blades is definitely something to consider. But it is more complicated than just aperture, as it has a lot to do with lens design and number of blades and shape of blades and shape of the aperture once the blades stop down. I like to post this example with an unmodified M 50mm f1.7. If it were wide open, the highlight bokeh would be perfectly round. But this is around f2, I think. Notice the hexagons have jagged corners:


Cosmic fly

[WPRESTO]

Part of the fixation on f1.4 is a leftover from an ancient photo search for something faster than f4.5 that also had good IQ, then came Tessar which could manage f3.5 easily, and f2.8 at 50mm, then Summicron and Biotar f2.0, etc. f1.4 became the benchmark for a normal focal length lens for 35mm. The speed chase was in part driven by "candid natural-light" photography, which for a while was THE THING to do as an independent photographer (remember, the search for f1.4 started in the era of flashbulbs and ASA/ISO 400 being super-fast but grainy). Some manufacturers brought f1.4 to 35mm FL lenses, 28mm lenses, even 24mm. Manufacturers seem to lavish more care on their f1.4 optics, so they outperform f2 lenses of the same FL. Also, as noted above the OOF effect of f1.4 is desirable, for example, to get a 3/4 facial portrait with a razor sharp eye, but slightly softened edges to the face, a pleasing effect. BTW: for beyond f1.4 there is also the Leitz 0.95 Noctilux (think that's the correct name) that even used goes for as much and more than the price of a K1.

[bdery]

Why is f1.4 so important?

I sold a FA50 f1.4, and (I think) nine copies of the F50 f1.7. My fastest lenses are the 40 and 100, both f2.8. So I'd say, to me, it's not important.

[Rondec]

f1.4 isn't particularly important. Most f1.4 lenses aren't even particularly usable at f1.4. There is a basic assumption that most lenses need to be shot stopped down a stop or so for good sharpness, so a lens that has a max aperture of f1.4 will hopefully be sharp by f2. But if a lens is well designed and max aperture is f1.8 and it is actually sharp at f1.8 (like the FA 77), then it is probably more useful than, say, the FA 50, where it really needs to be shot at least at f2.4 before images are decently sharp.

[pathdoc]

The speed chase was in part driven by "candid natural-light" photography, which for a while was THE THING to do as an independent photographer (remember, the search for f1.4 started in the era of flashbulbs and ASA/ISO 400 being super-fast but grainy).

Do you think if we'd had electronic flash sooner (hypothetically the magic flash fairy comes along and grants it to us), things might have taken a different path? With light on tap whenever we needed it, would the onus of the candid photographers then have been placed more on the film companies to improve the grain of their faster films?

The electronic versus flashbulb debate is had in my edition of Keppler's "The Pentax Way" (1972, incorporating the Spotmatic ES but not the F), when both were still very much contemporary; even then, with the expense of the electronic units being admitted, the practical concerns were leaning away from flashbulbs because of their one-shot nature and the need to change them to continue shooting.

[Macario]

it is important in low light photography. and then mainly that it is easier to compose, because the image will not be so dark.

[From1980]

Won't a brighter viewfinder image with shallow depth of field actually make critical focus more precise? I quite enjoy manually focussing my A50/1.2

Right on. Absolutely correct, for that A lens, or M and K, on viewfinders of cameras in the film era they were made to match, that is. Smaller, dim viewfinders in many DSLRs without the focusing aids we used in film cameras make manual focusing difficult with any lens. The inherent tolerance for manual focusing errors that slower lenses provide because of more depth of field wide open becomes relied upon by many so a lot of people just never become very good at manual focusing using a DSLR.

[Marktax]

Definitely worth discussion over a beer . . . . (SMC-A 50mm 1.4)