[cali92rs]

That depends on where diffraction starts to kick in:

Sigma AF 8-16mm f/4.5-5.6 DC HSM - Lab Test / Review - Analysis

You are correct, I made a generalization. Exotic telephotos are also optimized for wide open shooting.

[starbase218]

Yeah, right. I hope you do understand that f stop by itself means absolutely nothing.

It's the nature of that f4 that matters. I'll take f4 of the Leica's Summicron over f4 of any commercial zoom at any time.
It is not if the lens is f4, but how that f4 is described optically and what is capable of.

For example, f4 on DA70 is absolutely stunning, better say incredible, and I'd pay full price of the lens even if it were that f4 to start from, (and not f2.4).

In theory, you are right, of course. And the DA 70/2.4 is razorsharp at f/4. But - and this is a big but - it would never have been f/4 anyways. Plain and simple because it's not interesting commercially to make an f/4 lens when it could have been f/2.4. Sure, you give up some sharpness, but you can say your lens is f/2.4, and that helps it to sell. Also, absolute sharpness helps little when you don't have enough light to use that f/4. Then you have to bump up the ISO, and you may lose sharpness because of that anyway. Or when you want better subject isolation. A big aperture is a creative tool as well.

[Apapukas]

That's because the DA and leica are stopped down when they are at f4. No lens is as sharp wide open as it is when it's stopped down. And that extra stop sure comes in handy when you are indoors.

That was probably true until Zeiss introduces the new 55mm 1.4.

Other than that, I agree with you, that having an extra stop (or more) is very handy.

[RonHendriks1966]

But it's unreal to order in Europe and USA for many years.

It's in stock in The Netherlands:

Pentax SMC FA 20-35mm f/4.0 AL objectief

[lytrytyr]

That was probably true until Zeiss introduces the new 55mm 1.4.

No, that lens gets sharper when it's stopped down.
Look at the MTF curves here:

http://lenses.zeiss.com/content/dam/Photography/new/pdf/en/downloadcenter/da.../otus_1455.pdf

[Fontan]

It's in stock in The Netherlands:

Pentax SMC FA 20-35mm f/4.0 AL objectief

Nice. Ordered a bunch.

[robbiec]

I wish Pentax would give us nice little data sheets like Carl Zeiss do.

[lytrytyr]

I wish Pentax would give us nice little data sheets like Carl Zeiss do.

+1

Wouldn't cost them anything, and would show they're serious.

[Fontan]

I wish Pentax would give us nice little data sheets like Carl Zeiss do.

Apparently none of the PR guys at Pentax have kissed the stone yet. Methinks that is where the problem lies.

[Uluru]

In theory, you are right, of course. And the DA 70/2.4 is razorsharp at f/4. But - and this is a big but - it would never have been f/4 anyways. Plain and simple because it's not interesting commercially to make an f/4 lens when it could have been f/2.4. Sure, you give up some sharpness, but you can say your lens is f/2.4, and that helps it to sell. Also, absolute sharpness helps little when you don't have enough light to use that f/4. Then you have to bump up the ISO, and you may lose sharpness because of that anyway. Or when you want better subject isolation. A big aperture is a creative tool as well.

Being a niche player, Pentax has one privilege rarely bestowed to other who are bigger and must play safely and predictably: they may satisfy true photographic indulgence of photographers looking for real art in images — not solely for the sake of super fast apertures, nor MTF charts.

It's the psychological and artistic quality of the image that is then explored. The reason I mentioned DA70 is not because its f4 is sharp. It's because that lens is a rare gem in digital photography, and especially f3.2-f5.6 renders such pleasing images it takes my breath away every single time.

Every company must do some compromise. Say, Leica must aim for fast lenses because they don't employ SR and their buying choices of sensor technology are limited. Zeiss does fast lenses too because they design lenses across systems, and they rise prices exponentially whenever excellence in the performance must match the apertures. Then lenses grow in size and price.

And when judging Pentax lenses, we shouldn't forget the SR. It allows us to buy that extra stop or two we wouldn't otherwise get, and in return bless us with a lens that is still pocketable, but comes with no compromises when it comes to its artistic performance, nor with a huge price tag.

The SR is a core value of the Pentax brand in the digital world. It gives them justification to do what they do best and to even better it, to be unique and deliver lenses that are nothing but true little gems. And today, SR gives them even an AA edge. Thus, I see them as a brand that really understands what is its inherent value, and are building on it. It is a different kind of a compromise than everyone else takes, yes, but the nature of that Pentax compromise I like much better and I'm willing to support them.

I think that is essential for users to understand; asking for a A. fast, B. small and C. excellent performing lens across all apertures in one lens is impossible. We can claim only two at any time, not all three.

Which two you pick? That is called a compromise.

[wed7]

Assuming I can afford this lens, this would be a perfect pair with my DA 70, for travel/street kit.

[fuent104]

Being a niche player, Pentax has one privilege rarely bestowed to other who are bigger and must play safely and predictably: they may satisfy true photographic indulgence of photographers looking for real art in images — not solely for the sake of super fast apertures, nor MTF charts.

It's the psychological and artistic quality of the image that is then explored. The reason I mentioned DA70 is not because its f4 is sharp. It's because that lens is a rare gem in digital photography, and especially f3.2-f5.6 renders such pleasing images it takes my breath away every single time.

Every company must do some compromise. Say, Leica must aim for fast lenses because they don't employ SR and their buying choices of sensor technology are limited. Zeiss does fast lenses too because they design lenses across systems, and they rise prices exponentially whenever excellence in the performance must match the apertures. Then lenses grow in size and price.

And when judging Pentax lenses, we shouldn't forget the SR. It allows us to buy that extra stop or two we wouldn't otherwise get, and in return bless us with a lens that is still pocketable, but comes with no compromises when it comes to its artistic performance, nor with a huge price tag.

The SR is a core value of the Pentax brand in the digital world. It gives them justification to do what they do best and to even better it, to be unique and deliver lenses that are nothing but true little gems. And today, SR gives them even an AA edge. Thus, I see them as a brand that really understands what is its inherent value, and are building on it. It is a different kind of a compromise than everyone else takes, yes, but the nature of that Pentax compromise I like much better and I'm willing to support them.

I think that is essential for users to understand; asking for a A. fast, B. small and C. excellent performing lens across all apertures in one lens is impossible. We can claim only two at any time, not all three.

Which two you pick? That is called a compromise.

SR is no substitute for fast shutter speed when your subject is moving.

[Digitalis]

That was probably true until Zeiss introduces the new 55mm 1.4.

The MTF charts for the Zeiss 55mm f/1.4 lens look a bit wobbly at f/1.4 - but that is to be expected. Even the Leica APO Summicron (a $7500 lens) has a small drop in contrast in the edges @ f/2


Though that is nothing compared to what the Canon 50mm f/1.8's simulated MTF performance indicates:

[Apapukas]

Thanks for explanation.

I guess I should pay more attention to what the numbers say instead of what some guy from that company tells

[Uluru]

SR is no substitute for fast shutter speed when your subject is moving.

Indeed, you are to shoot moving subjects with a widest aperture possible, preferably f/1.4, so the every tiny bit is in tac sharp focus.