Are 'fast' lenses less important with modern DSLRs?

Film had a fixed ISO/ASA and although you could push it, you were generally somewhat bound by this and so the faster the lens (hence more expensive) the better your chances of getting nice results.

With digital you can set the ISO a bit more arbitrarily so you can use a slower lens and get the same shot, at the expense of some noise perhaps.

However as sensors improve and get better and better at higher ISOs are we getting to a point where you don't need to spend the extra money on getting those fstop improvements in speed?

Assuming all other things are equal in terms of sharpness and resolution, will you need to spend twice as much on an f2.8 versus a f5.6 (for example, this is hypothetical) if you will be able to set a higher ISO and get just as good results with no noticeable worsening of noise?

Like all things, you match the compromises to suit the situation.

If I can't use a tripod for a low light shot, then without hesitation I up the ISO. A sharp noisy picture would be better than an unsharp one IMHO.

I have an f1.4 lens, but the downside is that if you use it as such then you have very little DOF. So I tend to use the 16-45mm f4 anyway, and it does just fine.

Thanks John, but maybe I wasn't very clear. I was asking whether we are getting to a point with improvements in sensors etc where there will be no point paying a premium for a faster lens, assuming all other things being equal.

I understand the DOF field issue. But the 16-45mm f4 versus 16-50mm f2.8 is a case in point. There is a huge differential in price for two lenses which will both do the same job give or take 5mm focal length, but one is faster and much more expensive.

It was more of a general question and observation. Back in film days it used to really matter if you were using 64 ASA film for example. The extra speed could make all the difference between getting a nice shot or messing it up in certain lighting. Now I am not so sure...

I agree with you, I'm not so sure either.

I do know that I don't feel any imperative to buy the 16-50mm f2.8 as opposed to my 16-45mm f4.....apart from anything else, do I need the extra bulk and weight?

Still f/2.8 and f/4 is one f-stop if that makes a difference indoors of shooting iso3200 or iso1600 then that is quite a difference in noise.
Good the sensor are getting better but a lower iso will always look better. Also the narrow DOF is important for some types of shooting as well.

The real faster F-numbers seems they are getting out of fashion, f/2.8 is good enough for almost every lighting I believe.

Ps. Typing this on my moms laptop and the keys are placed just a bit differently then with mine so had some typos

Stefan, let's assume sensors keep getting better and in a few years' time you'll have a sensor that yields the same noise and quality at ISO 3200 as your current one does at 100 for example, surely we are getting to a point where your lens speed will become far less important than it has been historically?

So my question is really this. Do we need to pay a premium for fast lenses if this feature will become less significant as all other aspects of DSLR design improve and supersede them?

Yes, if you still want depth of field control.

No, if you don't.

That seems to be the simple answer.

However, as someone said "In theory there is no difference between theory and practice, but in practice there is!"

Generally the brighter lenses are aimed at pro markets - who expect much from the lens. A case in point is the SMC-DA*50-135. This past weekend I took some family shots at a gathering. The DA17-70 shots were great, but the DA*50-135 candid portraits were utterly, utterly stunning - taken at f/5.6 (even if I say so myself )

With all things it's something of a balancing act I'm happy to up the ISO to get what I want (like a reasonable DoF and a touch more resolution). However, there are also times when f/2.8 at 135mm is fabulous for subject isolation, and even f/4 won't cut it

That said, in line with what you've said, I find I use the DA17-70 in situations where I would normally use the 50mm f/1.4 The resolution on the new zoom is superb, and the versatility just makes it so much more usable.

Difficult question to answer

Matt

Well, I don't know if there is software that can do it, but theoretically you could also create the illusion of a shallow depth of field through a software algorithm in PP. Pick the spot you want in sharp focus and you could probably adjust the foreground and background to taste and create bokeh (that fashionable word of the moment) by layers in your PC just like you are now creating HDR.

you CAN do depth of field bluring in software, but it is difficult and rarely ends up looking good.

much better to let nature do it with a nice fast lens.

Also upping the ISO is all very well, but eventually you're going to run out of ISO range to up. If you and I have the same camera body, with super low noise ISO 6400 and SR, but my lens is 2 stops faster than yours guess what, I can still shoot in light 2ev darker than you can.

In another note, there is a common misconception that sensors will always keep getting less noisy with higher pixel counts. This is fundamentally untrue. The photoelectric effect (on which CCD and CMOS sensors are based) is a quantum effect. As such there is an in-built level of random noise which is just an inherant property of the universe in which we live. As we approach the quantum limit, R&D departments will have to put in more and more effort for less and less effect in terms of noise reduction as the factors they can alter cease to dominate. An image captured by counting a few tens or hundreds of photons at each photo site will always be noisy no matter what you do. Research grade CCDs are already at that point, so we don't have very far to go.

Here is a photo I manipulated in Corel Paint shop pro, it's called depth of field in the program, I took it with the X70 I was just experimenting
https://www.pentaxuser.com/photo/Purple-8085/large

that's nice but isn't really a DOF effect, you'd achieve that on film using a filter.

The problem with doing DOF effects digitally is that the computer doesn't know which bits of the scene to blur. If you're very skilled it can be done manually, but it's pretty hard (I've tried it a few times but only made it look ok once).

Photoshop includes a proper "Lens Blur" filter - but effective use of it requires creating an accurate focus depth map first. I've used it many times - it's very effective indeed, but it can be very time consuming
Matt

Yes I know what you mean, I still have the filter from my wedding days, you can vary the amount of effect in the program and that's what I ended up with.

That's what I was getting at. Surely you can build up layers of the same shot theoretically and tell it which layers are sharp and which are not, just as you might use different exposures of the same shot to crate HDR