Lens sharpness

Everyone seems to be obsessed with tack sharp images these days and lens MTF resolution figures. So while on this bandwagon why is that the Pentax lenses and other lenses in Pentax mount often (not always) score lower for sharpness than the Nikon equivalents.

A prime example of this is the Sigma 35mm 1.4 tested on Nikon D7000 and Pentax K5. It's rated as better in every way on the Nikon.

http://www.dxomark.com/Lenses/Compare/Side-by-side/Sigma-35mm-F14-DG-HSM-A-Nikon...

Unfortunately DX0Mark doesn't give exact MTF figures but you get the idea.

Then take for instance the insanely cheap Nikon Nikkor 35mm 1.8 DX. It's sharper than everything Pentax has in the 28-35mm range including all of their limited lenses.

http://www.photozone.de/nikon--nikkor-aps-c-lens-tests/628-nikkor3518dx?start=1
http://www.photozone.de/pentax/735-pentax31f18k5?start=1

It's a similar story right down the range over at DX0Mark. Filtering lenses by mount, tested on similar bodies (using the same sensor) and the Nikon offerings come out on top.

It seems it's only the older 3rd party lenses that compare well on the Pentax system, like the Pentax (tokina) 12-24mm and the Sigma 10-20mm (viewing results at 10mp on Photozone.de)

Anyway, sharpness isn't everything and the figures aren't all that important, I'm just curious (since it's dark cold and wet outside) as to why the Pentax doesn't score as well on the lens front when the bodies score higher or the same for image quality.

It's often down to interpretation of results and the way measurements relate to actual image quality and characteristics. "Sharpness" doesn't exist as a measurement, but resolution and contrast do.

A low resolution, contrasty image will look sharper to our eyes than a high resolution low contrast one. Then there are considerations of gradation, smoothness of what is these days called bokeh and of course it's all in relation to which camera bodies lenses are used on.

I've done some lens measurements and the 31mm and 77mm measure higher figures than the 43mm, but of the three it was the 43mm I kept. It has the best overall look and feel to the images, for me at least. Likewise, the 70mm Limited measures lower than the 77mm, but I prefer the 70mm.

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Best regards, John