[paperbag846]

most lenses and most shots, we won't be using ultra fast f-ratios, or will we?

No, we won't. Thats why it's best to think of "fast" lenses as special effect lenses... unlike the past, where they were considered necessary for fast-enough shutter speeds in a wide range of conditions.

That said, f2 is very functional, and most f1.4 lenses look amazing at f2.

[anthers]

Yes

Some points:

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

What he said.

I find that there is a big difference between f2.8 and f4, even on APS-C. I find that 2.8 is probably the upper limit of what I like to have available when doing subject isolation at shallow DOF.

[civiletti]

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.

That's the idea behind the codpiece, methinks.

[northcoastgreg]

Pentax certainly thinks that we don't need as fast lenses anymore

Is that the issue, or is that Pentax doesn't think we can afford fast lenses, so that they can't make money selling them?

I agree with the other posters that ultra fast lenses are more for artistic effects than low light. Having recently added a K 50/1.2 to my collection, I have to admit that the lens does not work all that well for general photography in low light. At f1.2, it produces soft, low contrast shots. But when used to create artistic effects with it's narrow DOF and astonishing bokeh, the lens is capable of producing very unique and extraordinary results.

[maverickh]

Fellow Pentaxians, thanks for the superb advise and comments. Now i have a better idea to the answer to my question.

It would also be helpful if some photos can be included to address some of the points mentioned.

Thanks and have a great weekend ahead.

[Pentaxor]

Is that the issue, or is that Pentax doesn't think we can afford fast lenses, so that they can't make money selling them?

I agree with the other posters that ultra fast lenses are more for artistic effects than low light. Having recently added a K 50/1.2 to my collection, I have to admit that the lens does not work all that well for general photography in low light. At f1.2, it produces soft, low contrast shots. But when used to create artistic effects with it's narrow DOF and astonishing bokeh, the lens is capable of producing very unique and extraordinary results.

f1.2 or any other faster lens are used primarily for portraits. and portraits are more pleasing with low contrast and soft rendering. these lenses are still great and useful for lowlight portraits. that is the main purpose of such fast lenses.

[Pentaxor]

Fellow Pentaxians, thanks for the superb advise and comments. Now i have a better idea to the answer to my question.

It would also be helpful if some photos can be included to address some of the points mentioned.

Thanks and have a great weekend ahead.

you can find a lot of samples in this link >>> PENTAX Photo Gallery

and this >>> http://www.pentaxphotogallery.com/home#section=EXIF-LENS&subSection=440&subS...12&language=EN

just browse along the images.

[Todd Adamson]

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?

Really depends on the shooter and the types of images they're trying to generate. Speaking for myself, I have shot many portraits at f/1.4:

[Class A]

A 2.8 lens on FF will have narrower DOF than the same lens on APS-C.

You cannot make such statements without providing further information. For instance, the same lens, using the same f/2.8, shooting the same subject from the same distance will show more DOF with an FF camera (because the APS-C image requires higher enlargement to yield the same output size, thus losing DOF).

That's why I said you either need the appropriate lenses on FF or you will be making different images (using less subject to camera distance).

Anyhow, I think for the sake of keeping the thread on topic we shouldn't continue this FF sidebar.

[Class A]

Speaking for myself, I have shot many portraits at f/1.4:

I like the second one, nice shot! The first one demonstrates the problem one often has with these kind of shots, AFAIC. The nose and ears are so out of focus that they exaggerate the depth of the face and thus create an almost comical impression.

Also, I find that such thin DOF almost mandates a "front on" pose, which has limited use. A bit of angle on the face and then having one eye in focus rarely works. I'm not saying ultra fast f-ratios don't work, but rather that their use is limited.

BTW, which lens did you use for these? Only using a tiny screen at the moment but they look very nice.

[Todd Adamson]

I like the second one, nice shot! The first one demonstrates the problem one often has with these kind of shots, AFAIC. The nose and ears are so out of focus that they exaggerate the depth of the face and thus create an almost comical impression.

Also, I find that such thin DOF almost mandates a "front on" pose, which has limited use. A bit of angle on the face and then having one eye in focus rarely works. I'm not saying ultra fast f-ratios don't work, but rather that their use is limited.

BTW, which lens did you use for these? Only using a tiny screen at the moment but they look very nice.

Thank you. These were done before I picked up a Pentax system, on my D3 with the 85/1.4D. I agree that this kind of thin DOF, especially on a very close portrait like the first one I posted, is a matter of taste, and not for every situation. But 1.4 has real value for me, possibly more than others. And yes, you have to have the eyes equidistant from the sensor, or have one more focused than the other. Although I have many of the latter portraits which I like, with only one eye in focus. Also, if your subject is further away, you have a little more room to work with, as in this shot, which was done with the same combo:

[maverickh]

Really depends on the shooter and the types of images they're trying to generate. Speaking for myself, I have shot many portraits at f/1.4:

Hi Todd,

I also encounter problem such as the first picture. The face is in focus but gradually fades away. Also one eye in focus the other is not. How did you managed to achieve focus in 2nd photo ? is it still taken at f/1.4 ?

[Nick Siebers]

I have several times used the A50/1.2 for taking pictures of my daughters' ballet and gymnastics lessons where lighting is bad, action is (somewhat) fast and flash would be distracting. Even down to f/1.2. It does get a little dreamy, with an interesting look, and yes I have to focus bracket to some degree. And sure, I know it is overkill. But the pictures have turned out noticeably better than with an f/2.5 lens.

[Todd Adamson]

Hi Todd,

I also encounter problem such as the first picture. The face is in focus but gradually fades away. Also one eye in focus the other is not. How did you managed to achieve focus in 2nd photo ? is it still taken at f/1.4 ?

Well...hehe...whether you call it a problem to have other features fade out is a matter of preference.

But yes, you do need to be careful the eyes are both in the focal plane, if that's what you want. And yes, I am sure the second shot was done at 1.4....but I didn't go back and look at the raw file; it very well could have been a deeper crop than the first.

[yeatzee]

Are fast lenses still necessary? ........ Yes.

I shoot at apertures between F/2.8 and F/1.2 nearly exclusively (with the exception of macro)...... I hate having a lot of the image in focus... gives me the P&S feel to images. (tasteful landscapes are an exception).