[maverickh]

During the film era when cameras did not have shake reduction capability or high ISO capability, I can appreciate the necessity for fast lens. However given the high ISO capabilities of the newer digital camera, such as the K-X, K-R, and K5, I wonder if it is still necessary to have fast lens, i.e. f/2 or f/2.8. Can the fellow Pentaxians kindly comment, from personal experiences.

[sterretje]

Yes

Some points:

Shallow depth of field
Clearer viewfinder
AF will be better (as the lens is still part of the measuring system)

[Lowell Goudge]

Fast lenses will always be in favor, over slow lenses for many reasons.

While SR was touted as eliminating the need for fast lenses, this is only true from the perspective (pun intended) of camera movement, not subject movement. SR simply cannot track subjects (Hey, maybe I should patent that Idea, tracking subjects with SR to keep them in the same spot on the sensor). So, for moving subjects you still need high shutter speed.


While better high ISO performance is a fact of life these days, high ISO performance will always have technical limits, and therefore there will always be a desire to get as much light to the sensor as possible, at some point regardless of high ISO performance the limit will always be the light coming through the lens.


Depth of field control still remains a need for artistic shots, and this can only be truely achieved with fast lenses, and this is becoming much more apparent with ASP-C format cameras, where the depth of field with wide angle lenses (equal FOV to film or full frame) is higher, This is what is pushing fast wide and ultra wide lenses today.


Even if you get high ISO image quality, AF requires light and contrasty images to focus quickly, the faster the lens the brighter the image to teh AF sensor, that can't be fixed with High ISO, and neither can a bright viewfinder. Bigger lenses make for brighter viewfinders.

So the answer is that there will alwasy be a demand for high quality fast glass, the only difference I can see is the possibility that the demand may shift slightly, considering that for many people the change in sensors will deminish the demand.

Having made that statement, however, you need to offset that by what I think is the increasing trend of photographers to experiment in artistic photography, because the cost of image processing to learn these techniques has gone from quite high to zero. You no longer need to spend money processing, and printing your mistakes, just pull them up on a screen. This tends to radically increase the number of shots people take.

My own shooting is indicative of this trend, where I shot roughly 20,000 frames between 1981 when I got my first SLR, and 2003 when I switched to digital, and I have shot well over 50,000 frames since. On average, you could say I shot 900 frames per year on film, and 7000 frames annually on digital, although I would admit that this went from a starting point of perhaps 5000 annually frames in 2003-4 to 13000 frames annually today

[paperbag846]

I think the original term "fast" has become only necessary for creative photography (f1.4 or f1.2). There is no other way to get that look, however. Before it was impossible to get a usable imagine in low light without one of these fast lenses.

Now, fast means between f2 and f2.8, which is a good compromise in my books. I find things such as autofocus tend to work better when the depth of field is a little larger, and the ISO advantage of a modern camera goes well over 2 stops.

However, if a lens moves past f2.8, you will being to run into situations you simply can't photograph ideally. The DOF will be too large for good subject separation, autofocus might have trouble with too little light, and you might have troubles with exposure in low light. Since most lenses must be stopped down a little bit to get the best out of them, I would settle on f2.0 being the new optimal fast aperture, which gives you f2 when you need it, or f2.8 for optimal quality.

This is all, of course, assuming you want that "fast look". Many excellent photographs (before, and now) have been taken at f8, where even lesser lenses will excel nicely.

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Last edited by paperbag846; 12-11-2010 at 11:04 AM.

[Eagle_Friends]

I think the original term "fast" has become only necessary for creative photography (f1.4 or f1.2). There is no other way to get that look, however.

Now, fast means between f2 and f2.8, which is a good compromise in my books. I find things such as autofocus tend to work better when the depth of field is a little larger, and the ISO advantage of a modern camera goes well over 2 stops.

However, if a lens moves past f2.8, you will being to run into situations you simply can't photograph ideally. The DOF will be too large for good subject separation, autofocus might have trouble with too little light, and you might have troubles in low light. Since most lenses must be stopped down a little bit to get the best out of them, I would settle on f2.0 being the new optimal fast aperture, which gives you f2 when you need it, or f2.8 for optimal quality.

This is all, of course, assuming you want that "fast look". Many excellent photographs (before, and now) have been taken at f8, where even lesser lenses will excel nicely.

i agree with that statement. most typical photographers wouldn't need a f1.2 lens, when a f1.4 does it's job fairly well already.

with quicker lens, the weight and the body of the lens increases. the other advantage i see if creamier bokeh, which is important for some people.

[Just1MoreDave]

Fast lenses are bigger - sometimes a lot bigger. It's one thing to brag about high ISO performance of your body, or having the best type of stabilization. But when they can see your big lens from a hundred meters away, bragging is not even necessary.

[kenyee]

i agree with that statement. most typical photographers wouldn't need a f1.2 lens, when a f1.4 does it's job fairly well already.

We don't even have a choice of f/1.2 in pentax land

And the 50/1.4 really is not very sharp at 1.4...needs to go down to f/2.8 or f/4 to be decent.

Lenses like the Canon 85/1.2 or the Canikon 200/2 are amazing for subject isolation and bokeh, particularly on FF.

So the answer is it depends on your style. If you like subject isolation, then fast lenses are still needed (unless you get a 10K 645D in Pentax land :-)
For sports, a good 2.8 with ISO cranked to ISO3200 is probably good enough indoors...

[Class A]

The term "fast" indicates the primary purpose of "lens speed" in the film days. They would have been called "shallow" or similar otherwise, right? So the purpose of allowing shorter shutter speeds is now better achievable through high ISO settings. I say "better" because one isn't forced to use very shallow DOF and doesn't need to use a lens at a settting where it has its weakest performance.

Pentax certainly thinks that we don't need as fast lenses anymore, otherwise the 55-135 - the equivalent of the common 70-200 of film days - would have had to feature a constant f/1.8. With the f/2.8 it has, we cannot take the same images as someone with a 70-200/2.8 on a FF camera.

I disput the claim that ultra fast lenses are better for AF. Such lens designs often feature significant aberrations which lead to focus shift. The AF determines the focus a) for one colour only and b) one aperture only so if the lens has high aberrations the real focus may be somewhere else for a given shooting aperture. I understand cameras try to compensate for focus shift but it doesn't always work perfectly. Ultra fast lenses also require more precision from AF systems as the margin of error is much smaller.

Having said all that there is still the purpose of allowing DOF control. While subject / background separation can also be achieved with PP it is easier and often nicer to do it with a fast lens. Often, in particular with longer focal lengths, I think f/2.8 will be sufficient though.

In conclusion I think that the hay days of ultra fast lenses are over and that the corresponding race has been replaced by the high-ISO race.

[Ash]

We don't even have a choice of f/1.2 in pentax land

Why need a choice when there's the A or K 50/1.2?

Of course the game would change if there was a D-FA 50/1.2!

Nevertheless, to the OP, it's clear from all the FF camera threads that thinner DoF is consistently sought after, and thus limits to APS-C cameras in this regard are what discourages some from sticking with Pentax, seeing as though there *are* a number of FF lenses Pentax has produced and are *still* producing but without even a hint from Pentax that there is any interest in producing a FF dSLR.

[Todd Adamson]

When I hear "fast lens," I think "DOF control" long before I think "low light shooting." To me, nothing is more fundamental to the aesthetic of an image, or its editorial/documentary purpose, than the choice of aperture. Sure, great high ISO performance means I can stop down more for the same shutter speed and light available. But stopping down means the resulting image is different.

In other words, yes.

[Class A]

Nevertheless, to the OP, it's clear from all the FF camera threads that thinner DoF is consistently sought after,...

Not so clear to me. Also, sensors do not create shallow DOF, lenses do. In other words, if you haven't got the lenses, a format change won't help you (unless you want to take different images (with a different perspective) which also happen to have shallower DOF).

Also, whether or not the perceived desire for thinner DOF is reasonable or not is another matter.

I just read an old Amateur Photographer issue where the Canon 85/1.2 was tested. The f/1.2 sample portrait just looked weird. BTW, the lens has a lot of lateral CA which doesn't disappear when stopping down. Great glass to look at but photographically it seems to make less sense than its appeal suggests.

[paperbag846]

I believe the A/K 50 1.2 is the ultimate for the fast look in pentax land, but the 1.4 is very usable for that soft/fast look (it's not good for shooting test charts), and the old 1.7's are little wonders at f2: for their price, they are absolute steals. It's unfortunate it's so hard to focus with the stock screen with the superfast manual glass.

I've read that a lens that fast (below f1.7) causes issues with the autofocus system. I haven't noticed it too much with my FA 50 1.4, but it sure hunts more than my DA 40 2.8, so maybe that's the issue (and a possible cause for all of the self-destructing FA 50 1.4s ). It's a shame. I don't think I would have much patients for a 600 dollar lens that is so challenging to manually focus (not that I can afford one anyways).

[Class A]

To me, nothing is more fundamental to the aesthetic of an image, or its editorial/documentary purpose, than the choice of aperture.

I fully concur but what are f-ratios that are still practical in terms of both a) usable DOF and b) usable IQ?

With an A* 85/1.4 or DA* 55/1.4 you might get the odd f/1.4 shot that works really well but with most lenses and most shots, we won't be using ultra fast f-ratios, or will we?

[Pentaxor]

Not so clear to me. Also, sensors do not create shallow DOF, lenses do. In other words, if you haven't got the lenses, a format change won't help you (unless you want to take different images (with a different perspective) which also happen to have shallower DOF).

Also, whether or not the perceived desire for thinner DOF is reasonable or not is another matter.

I just read an old Amateur Photographer issue where the Canon 85/1.2 was tested. The f/1.2 sample portrait just looked weird. BTW, the lens has a lot of lateral CA which doesn't disappear when stopping down. Great glass to look at but photographically it seems to make less sense than its appeal suggests.

the Canon 85/1.2 eventhough it is an f1.2, is somehow a dud for an "L" quality lens. what I didn't like about it is the chopped bokeh and as you mentioned, lateral CA. personally, I prefer the old manual focus 85/1.2.

[kenyee]

Not so clear to me. Also, sensors do not create shallow DOF, lenses do.

To be clear, size of sensor and lens aperture size both affect DOF. A 2.8 lens on FF will have narrower DOF than the same lens on APS-C.
Forgot about the 50/1.2...no longer being made but you can still get it used...MF only which is harder w/ such narrow DOF.