K20D and P(MTF)

I've been using P(MTF) quite a bit and particularly for street photography believing that at this setting my lenses would perform at their best. In some instances the results have been quite surprising with apertures being much wider than I would have suspected. On an average sunny day with the same subject matter here are my findings of what the camera selects:

DA 18-55 @ 18mm = f4.5
DA 18-55 @ 55mm = f6.7

DA 16-45 @ 16mm = f4
DA 16-45 @ 45mm = f5.6

DA 50-200 @ 50mm = f4.5
DA 50-200 @ 200mm = f6.7

DA 40 LTD = f4

I must say I'm very surprised at the 'wide open' results

But how did the pictures look?

I must admit to being quite sceptical regarding the usefulness of MTF, consequently I've never used it. It's interesting to hear how your shots have turned out using the setting though

Simon

The pictures are fine of course, I'm just surprised at the results since received wisdom and anecdotal evidence suggest these lenses perfom best stopped down a bit more. Pentax clearly think differently.

It is true that theory says that best resulots will be had at wider apertures, but that depends on a more or less perfect lens design.

Most zooms performa better stopped down more. I wonder if they have assumed no decentering for the MTF values - in other words, the theoretical best performance assuming a perfectly assembled lens.

I think you might be right John, primes are so good that perhaps it doesn't matter much which f-stop you use but with zooms it must be based on theoretical lenses.

Interestingly, though, my 18-55 at f6.7 is stunningly sharp but I still would have thought that the zoom figures might have been the other way round.

It may be that the selection is a compromise between sharpness and bokeh(...or depth of field).
Although I have to say I have been quite suprised how sharp many of my lenses (older primes and DA kit zoom) can be at maximum aperature under the right lighting conditions.

I'm still using F8 and be there.