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04-12-2013, 11:02 AM   #46
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QuoteOriginally posted by tclausen Quote
24ish mm, OK, but not f/2 - make it an f/1.2, and it'd be a winner!
But for digital, such speed is wasted:

DxOMark - F-stop blues

That's why the DA Limiteds make sense.

04-12-2013, 11:07 AM   #47
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QuoteOriginally posted by lytrytyr Quote
But for digital, speed is wasted:
Speed wasted? Perhaps with respect to overcoming low light conditions; but shallow DOF seems to be extremely important to some, so a large maximum aperture is even more important on APS-c than it is on larger formats.
04-12-2013, 11:16 AM   #48
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QuoteOriginally posted by Parallax Quote
Speed wasted? Perhaps with respect to overcoming low light conditions; but shallow DOF seems to be extremely important to some, so a large maximum aperture is even more important on APS-c than it is on larger formats.
Unfortunately, focusing then gets so hard,
at least for non-static subjects,
that the only reliable technique is focus bracketing.
04-12-2013, 12:15 PM   #49
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QuoteOriginally posted by lytrytyr Quote
But for digital, such speed is wasted:

DxOMark - F-stop blues

That's why the DA Limiteds make sense.
I think that the link you cite says it all: "I am therefore inclined to question the real benefit of faster lenses..." That's a mighty fine inclination to have, and one should always question everything .... but some guy doing that doesn't make it a fact

Yes, the benefit gain (in terms of light falling on the sensor) may be marginal at wider apertures....then again, sometimes margins do make the difference. And in any event, that's only half of the story; DoF is another kettle of fish.

So, to me, the DA Limiteds make very little sense in that regard: they're supposed to be top-of-the-line, yet they do not go that extra step.

I love that the FA Ltd were f/1.x lenses, and was (and am) hugely disappointed to see that the DA Limited went f/(>2.x).

This is a strictly unscientific, subjective and possible "apples-to-oranges" test but I can clearly see the difference in both brightness (viewfinder, AF) and DoF on the DA Ltd 70/2.4 and the FA Ltd 77/1.8. While not identical, the focal lengths are "sufficiently similar" for the comparison to make sense to me.

I fully appreciate that making f/1.x lenses carry costs, but as the Ltd range is supposed to be "top of the line" I'd like to see a couple of more f/1.x.

Yes, the 55/1.4 renders me ecstatic ... I used to love the Olympus Zuiko 50/1.2 - in case you didn't figure, my "inclination" is towards faster glass (& to think that the DxOMark dude is mistaken )

04-12-2013, 12:27 PM   #50
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QuoteOriginally posted by lytrytyr Quote
Unfortunately, focusing then gets so hard,
at least for non-static subjects,
that the only reliable technique is focus bracketing.
Well, I've not used an f/1.2 on APS-C. I regularly use f/1.8 and f/1.4, though, also fully open - and that without focus stacking.

Of course, when selecting exposure parameters one should always keep in mind that the shallower the DoF, the less tolerance for subject movement post-focusing. I'd say that for a wide-angle f/1.2 is no worse in that regard than a (say) 200/2.8....
04-12-2013, 12:44 PM   #51
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QuoteOriginally posted by lytrytyr Quote
But for digital, such speed is wasted:

DxOMark - F-stop blues

That's why the DA Limiteds make sense.
Absolute rubbish. Did not happen the last time I tried with a K-7 and a M50 f1.4. Must be something that only Canikon people get
04-12-2013, 02:36 PM   #52
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QuoteOriginally posted by kh1234567890 Quote
Absolute rubbish. Did not happen the last time I tried with a K-7 and a M50 f1.4. Must be something that only Canikon people get
Now we seem to have the DxO effect confounded with the step-down ring aperture effect.
These tests are more convincing under clearly stated control conditions,
without any "post-proc exposure tweak," testing one thing at a time.

For starters, is it known that the K-7 makes no unreported ISO change?
04-12-2013, 02:42 PM   #53
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QuoteOriginally posted by tclausen Quote
I think that the link you cite says it all: "I am therefore inclined to question the real benefit of faster lenses..." That's a mighty fine inclination to have, and one should always question everything .... but some guy doing that doesn't make it a fact
Doing what? A lab test?
Don't be misled by the Francophone phrasing of the report.

04-12-2013, 02:47 PM   #54
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QuoteOriginally posted by lytrytyr Quote
Doing what? A lab test?
Don't be misled by the Francophone phrasing of the report.
I live in France and speak the language (albeit not natively).

An "inclination to question" does still not a fact make.

Also note that even if an extra stop on wide apertures mean "less extra light on the sensor" than an extra stop on a slower aperture, it does mean extra light & a different DoF, still - and it'd make a lot of sense for the Ltd to offer that.

Last edited by tclausen; 04-12-2013 at 02:54 PM.
04-12-2013, 02:56 PM   #55
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Getting back to the original question... My opinion is that Pentax `owes' us a DA 28mm, preferably of the limited variety. My reasoning is that the 21 ltd more or less reproduces the 31mm FL on APSC, and any of the various 50mm reproduce the 77mm FL on APSC, so all that is missing is 43/1.54=27.92 mm lens...
04-12-2013, 03:32 PM   #56
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QuoteOriginally posted by lytrytyr Quote

That's why the DA Limiteds make sense.
If a prime is not a stop faster than a zoom in the range then it doesn't make sense to me.

The idea of slow DA limited primes may have made sense a few years ago for size reasons, but in the age of mirrorless cameras the "compact" reason is no longer a good one. FA limiteds ironically make more sense now that DA limiteds in this current environment.
04-12-2013, 03:35 PM   #57
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QuoteOriginally posted by lytrytyr Quote
Now we seem to have the DxO effect confounded with the step-down ring aperture effect.
These tests are more convincing under clearly stated control conditions,
without any "post-proc exposure tweak," testing one thing at a time.

For starters, is it known that the K-7 makes no unreported ISO change?
It is a manual M type lens. The K-7 has no way of knowing the speed of the lens or the actual set aperture. If you look at the EXIFs, all the test shots were taken with the camera in manual mode, same ISO, same shutter speed. All that had changed was the aperture setting on the lens. Obviously, I also had to manually edit the EXIF f-stop fields, which would record as zero, mainly for the benefit of anyone viewing the shots on Flickr which picks them up during upload.

The 'post-proc exposure tweak' was simply to set the image exposure right on the first (f1.4, no hood) frame in SilkyPix Pro 5 and then to adjust all the other shots by the exactly same amount. If you wish, I can put the PEF files on the net and you can play with them yourself. Ignore the bottom row of the shots, they are not relevant in this case.

You could do your own test, I just thought that this example, which I already had on the forum, was a good way to show that the DXO write-up did not seem to apply to the K-7 M50 f1.4 lens combination.

If you'd like to discuss this further then we should really start a new thread rather than hi-jack this one.

Last edited by kh1234567890; 04-12-2013 at 04:11 PM.
04-12-2013, 04:08 PM   #58
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QuoteOriginally posted by kh1234567890 Quote
If you'd like to discuss this further then we should really start a new thread rather than hi-jack this one.
I'm going to be offline for a day or two,
but the issue does seem important enough
for us to try and get it resolved on the forum,
even though my original quote was somewhat light-hearted,
responding in kind to a proposal for a 24/1.2 DSLR lens.

DxO generally seem serious,
so a priori I would trust their test results 90%.
However, the D3 versus D3x values suggest
that number of pixels per mm alone isn't a factor.
04-12-2013, 05:05 PM   #59
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I think you guys are right. Personally, I couldn't care less about DoF, but a prime being f2.4 or f2.8 really limits its usage in dark situations. If it were under f2.0, it could take much less noisy photos in dark situations. It would also make sense, as people pointed out, in relation to zoom lenses. What I would love to see is if Pentax would add a couple more fast primes, especially in focal lengths other than 50-55. But who knows what Pentax is planning. On the one hand, its great that Pentax offers so many high quality primes, on the other hand, only a couple ones are fast, and those are pretty expensive. And only one is WR. It just seems like a lost opportunity. A niche they could have targeted better.
04-12-2013, 06:05 PM   #60
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There was a DA*30mm on the 2008 roadmap. Rumour said it was to be f1.4.
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