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02-01-2011, 07:44 PM   #1
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K5 and photozone

I read and compared camera bodies until I was blue in the face and finally decided on the K5. That was a week ago and the decision hasn't wavered. Good. And of course, I'll need a lens. It was recommended that I go to Photozone for a reliable review of Pentax lenses. Is it possible to compare the reviews of fixed focal length lenses to the reviews of the zooms. The 17-70 is rated 1/2 star better than some of the limited fixed focal lengths, like the SMC DA 21. When reading up on the K5 it seems everyone was endorsing the limited lenses as the best in the business. Is this a case of apples and oranges? or does the 17-70 really have a bit better optics than, for example, the SMC DA 21? Any comments about how to understand Photozone would be much appreciated. Or maybe Photozone isn't considered a good resource? Thanks.

Bluekorn

02-01-2011, 08:24 PM   #2
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I would look at the MTF50 data on photozone to get a better feel for IQ, but just know that different sites will have different MTF50 test results so if you go that route only compare on the same site. As for cross comparing, I would think that each lens, no matter zoom or fixed, would be put through the same test and the results should be stand alone and not on "class" specific.
02-01-2011, 08:45 PM   #3
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Being an engineer, I looked at the MTF graphs and ignored their star rating system.

Be warned, however, that I have read several times on this forum, that the numbers can be misleading.

Since photography is art (IMHO), even if the 'center sharpness' is bad on photozone, it might be that it is bad in a very pleasing way. It could also be that an improvement in something that wasn't measured on photozone makes the lens with worse MTF numbers at the edges a better lens for what you want to use it for, for example.

Anyway that's my 2 cents.
02-01-2011, 09:23 PM   #4
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1)
3 stars might actually be 3.4999 stars rounded down
3.5 stars might actually be 3.5000 stars

How big is that difference? As we don't know how they exactly rate a lens, stars are not the holy grail. Check the numbers on the analysis pages, not the stars

2)
Primes are in general better than zooms; maybe I should rephrase that. It's easier to design a good prime than a good zoom as a prime can be optimized for one focal length. This however does not mean that a manufacturer can not design a bloody good zoom or can not design a bad prime (not saying that the DA21Ltd is bad)

02-02-2011, 12:39 AM   #5
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In my opinion, www.photozone.de and www.slrgear.com provide some useful independent reviews that complement nicely the Forum user reviews. Many user reviews tend to lack objectivity, but the independent reviews tend to be more objective.

Personally I value the objective reviews, especially when there is some consistency across more than one website.

If I use my own, limited experience, I would say that www.photozone.de was quite accurate in its assessment of my lenses (see signature). I would have possibly rated higher the Voigtlander Nokton 58mm f1.4 (*) by 0.5 stars overall, but all other lens assessment were quite consistent with my own opinion as an user..

(*) Photozone.de did not test the Nokton 58mm on a Pentax but I used their Nikon APS-C test as reference.

Hope that the comment will help.
02-02-2011, 02:15 AM   #6
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QuoteOriginally posted by bluekorn Quote
The 17-70 is rated 1/2 star better than some of the limited fixed focal lengths, like the SMC DA 21.
Single benchmark figures (like a star system or the DxOMark) are always problematic because they imply a weighting of individual contributions that may or may not fit your own value systems. The Photozone editor may think that sharpness is more important than smooth bokeh and this will influence the stars awarded. If you were after smooth bokeh, his stars wouldn't work well for you.

Furthermore, it is not completely impossible that a zoom outperforms a prime if the latter embodies optical compromises that were made to make the lens as small as possible. Or, the prime was designed to give a certain look (e.g., smooth bokeh) and hence doesn't perform well in another discipline that was important to yield more stars.

Photozone tends to focus on basic lens properties such as sharpness, CA, vignetting, etc. Most modern lenses fare well in these disciplines anyhow so if I were you, I'd rather look at sample images from lenses in question and see whether you like the bokeh, the subject/background separation, etc.
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