You write that you took some photos at a wedding that generally you were happy about. Then you took some portraits, (some prefer the 50-135 for portrait work), and mention that the focus might need to be corrected. Then you go on with your homemade test set-up.
You’re comparing your DA* 16-50/2.8 lens wide open, to a 50 mm prime (much easier to make). You’re showing examples for a use, in which the DA* lens is not designed.
It is a lens, meant to be used for objects at intermediate and long ranges, not close-up copying work. The idea is, how a lens that is well corrected for infinity use is not necessarily corrected for use at close range, and vice versa.
A fast zoom lens that goes from 16 mm, is a fairly extreme design. It sounds like you would be happier with the Sigma 18-50 f2.8 MACRO instead, or continuing with primes.
Dedicated macro lenses are aberration-corrected for use at close range, including astigmatism, field curvature and distortion to enable copying work. Here the upcoming DA 35/2.8 Macro limited, will probably do the trick better for you.
http://www.vanwalree.com/optics/astigmatism.html
“Astigmatism in practice
Sure, when a lens is used at full aperture the corner definition is often noticeably worse than the center definition and the above aberrations can be (partly) responsible, but it's no trivial matter to tell them apart from other oblique aberrations.”
Lance had a discussion of the DA*16-50 f2.8 @ f2.8 :
“I am not too sure that we take photos of landscapes at f2.8, I know I never do. Generally I will be taking a landscape with apertures of f5.6 and greater. I am also not in the habit of taking flat plane photos of brick walls either. If I want a flat field type lens, I will use a prime that exhibits this advantage.
If you are using the lens at the longer end, then it is generally to pick out a subject or for portraiture and it is generally the central area that requires a sharp image quality.
All lenses are softer at the corners and maybe this is a little softer at the corners, but we are talking about f2.8, not f5.6 or f8 etc where it seems to be quite good.”
http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=24841259
And he said in another thread :
“At f2.8 this lens is generally not used at 16mm, but more likely to be used at 30mm or 50mm etc. Expecting flat field sharpness at 16mm and f2.8 is a bit of a tall order for a prime let alone a zoom and I think it not something that is critical.
I am almost tempted to say that if they require less distortion at the wide end that a zoom is not the answer. Having said that, even my FA20 exhibits quite significant distortion of 2.5% and thats on APS C! ;-)”
If you want more sharpness in the corners at extreme wide angle and wide open, you should go for the 14 mm prime. Here is James real world comparison :
http://www .
pentaxforums.com/forums/pentax-slr-lens-discussion/14607-da-14mm-f2-8-vs-da-16-50mm-f2-8-wide-end.html
(Just put the URL together, to get access to the forum)
A great lens for architecture work, was the A 15/3.5. But from new that was a 1.600-2.000 Euro lens. It was later sold under Zeiss as well.
For taking pictures at ceremonies, I might bring two bodies. One with a tele lens, and one with a WA/normal lens.
Hope things will work out for you. Whether you find it to be okay for the work you expect to do with it, take it back to have it adjusted; or trade it for a different lens more to your liking.
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Kind regards
Sune
“The K10D not only proves that Pentax belongs in the big league, it’s an all-star player.” Popular Photography & Imaging and American Photo. Jan 07
