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12-27-2007, 02:07 PM   #1
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DA Limiteds: Smaller Max Aperture

Why do the DA Limiteds have a smaller maximum aperture in comparison to the FA Limiteds at similar focal lengths?

12-27-2007, 03:59 PM   #2
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QuoteOriginally posted by tux08902 Quote
Why do the DA Limiteds have a smaller maximum aperture in comparison to the FA Limiteds at similar focal lengths?
The current DA* lenses are zooms. A 16-50 f/2.8 is really rather fast, as is the 50-135/2.8. The single focal length limiteds can be optimized for a larger aperture. Generally speaking the fastest lenses are "primes", single focal length lenses.
12-27-2007, 04:10 PM   #3
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QuoteOriginally posted by tux08902 Quote
Why do the DA Limiteds have a smaller maximum aperture in comparison to the FA Limiteds at similar focal lengths?
I suspect it was a design trade-off to keep the DA lenses as small as possible.
12-27-2007, 04:26 PM   #4
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However, I assume they are still pretty fast with those apertures because the DA* zooms have maximum apertures of 2.8, as well, and they are regarded very highly.


Last edited by tux08902; 12-27-2007 at 04:46 PM.
12-27-2007, 04:31 PM   #5
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QuoteOriginally posted by Canada_Rockies Quote
The current DA* lenses are zooms. A 16-50 f/2.8 is really rather fast, as is the 50-135/2.8. The single focal length limiteds can be optimized for a larger aperture. Generally speaking the fastest lenses are "primes", single focal length lenses.
Err... if you read tux08902's post, I believe he's referring to the DA Limited vs FA Limited prime lenses, not the DA* lenses.

The DA Limited lens focus on being small and compact in size. The trade-off for this is a slightly smaller maximum aperture when compared to the FA Limiteds.
12-27-2007, 05:14 PM   #6
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I would agree with creampuff above, but I also think that they were trying to keep costs down a bit. The DA ltd's are significantly less expensive than their FA ltd counterparts, part of that savings is reflected in the larger apertures.

NaCl(there are always tradeoffs)H2O
12-27-2007, 05:18 PM   #7
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Plus I think there is an inherent speed trade off in the pancake/sharpness equation. Ie. pancakes in general are slightly slower than the regular lens formulas.

But that's part of the design brief, as mentioned above: compact, light, elegant.
12-27-2007, 05:26 PM   #8
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However, don't prime lenses generally need to be stopped down to get real sharpness. I've noticed this with my M50/1.7. I'd assume then, that the slightly larger apertures are not that big of a deal.

12-27-2007, 05:44 PM   #9
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basic/somewhat off point question

What are the advantages/disadvantages of using the DA Limited primes with the K10d body as opposed to the FA Limited primes?

Bob
12-27-2007, 06:08 PM   #10
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Generally speaking yes, however all lenses (primes and zooms) usually reach peak sharpness at f/8, +/-1 stop, not just primes. But some lenses show marginal improvement such as DA 40/2.8 or FA 35/2 that it really does not matter are they stopped down or not. Some improve considerably, like M/A/FA 50/1.4 or M 40/2.8.

But one thing is also important: with fast lenses (f/2, f/1.7, f/1.4) focusing is critical since depth of field is razor thin (especially at short distances) and ANY focusing error results in loss of sharpness. This should be also taken into account while estimating sharpness wide open.
12-27-2007, 06:45 PM   #11
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QuoteOriginally posted by RJL Quote
What are the advantages/disadvantages of using the DA Limited primes with the K10d body as opposed to the FA Limited primes?
Bob
Advantages of DAs: smaller size/weight, lower price, quick-shift focus, faster AF.
Disadvantages: smaller aperture, slightly less attractive bokeh (very subjective though), not future-proof in case Pentax goes 1.1x crop, not the same "feel" of craftsmanship in the FAs.
12-27-2007, 06:49 PM   #12
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There's the quick shift manual focus feature of the DA vs. FA. The FA's have an aperture ring and can be used with film cameras. DAs can, as well, though they aren't 'recommended' due to possible vignetting. The DA 40 I think actually is a full frame lens.

The FAs have a faster max aperture, which can make a difference - though it's not a huge difference. The DA's may focus faster. In comparable focal lengths, you should check close focus distance / magnification factor if that's important to you. There are some differences.

Pixel peeping or resolution testing wise, the FA's probably peak at a higher resolution than the DA's, but the DA's have a more even resolution to the edges while the FA's lose a bit towards the edges. Bokeh-wise, each lens has its proponents and detractors.

I should mention that in the design tradeoff game, the fast Sigma primes are an extreme example of max speed overriding most other considerations: they seem to be soft in the corners and at max aperture, and they aren't as petite as the Pentaxes. However, other brands have the reputation (and test results) that tend to be more even in resolution across the frame - Pentax historically has favored center over corners in their designs. The DA pancakes are an exception to this.

There's another school of thought that says all Limiteds are overpriced, that the true classics are the 50 and 35.

But that's all part of the fun.
12-27-2007, 07:16 PM   #13
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All lenses will perform better stopped down a bit. Generally speaking a lenses sweet sharpness spot is about 2 stops down. This is a general statement, and lenses will vary.
12-27-2007, 07:40 PM   #14
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Are the DA Limiteds subjected to the 1.5x crop factor limitation? I'm reading reviews and they all refer to an effective field of view. That makes me wonder because I always thought DA lenses were built for digital, and therefore, were not affected by the crop factor.

I think I'll go with the DA Limiteds, though. Having all three would make a nice, light kit for most applications. That's what I'm looking for. I generally do not like to use zooms.
12-27-2007, 08:36 PM   #15
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My only grouse with the DA lenses is the absence of an aperture ring, which is useful for certain macro set-ups.
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