I have just returned from a short business trip to Japan for several days and came across the Bic Camera shop and tested the DA 15 lens on my K-m hands-on myself.
The good news is that the DA 15 lens that I tested is actually not that bad in IQ as what the DPR found (and posted). I am almost certain that Pentax UK just sent the DPR a very bad copy, which I think Hoya/Pentax have always been so causal/careless but actually stupid each time when they sent DPR some gear to test.
The DA 15 I tested has good IQ wide opened. The corner sharpness is acceptable. There is no obvious vignetting as what we can see in the test review of the DPR.
As I have been thinking to acquire the DA 15 since it was announced, I decided to buy the lens shortly after my brief testing. Indeed, the lens is far cheaper than what I could get it in Hong Kong, at about US$600 at the Bic Camera (Vs $850 in Hong Kong - that price is just crazy for such a slow prime! $600 is not cheap neither IMO). The sales person got a new box for me and I shortly found a problem with the lens cap, which was just too obvious. The lens cap is a screw-in type (metal material which looks good and felt elegant but for practical use, it is just a joke). It was officially told that the PENTAX logo should stay upright when the cap is fully screwed in but unfortunately it was not so for that copy. It inclines at more than 10 degrees (approximately) to the left when looking from the lens front. So, I asked to get another copy.
So, the salesman got me another copy then. The logo position had no problem that time but more unfortunately, that copy seemed to have been mishandled and there was two small scratches on the glass elements which could be easily seen when I looked through the lens wide opened. Well, this may not be a Pentax factory problem though, anyway..
Since that shop has only two boxes of the DA 15, I went to another branch shop nearby. There was a new box sitting there and I felt happy and thought that I was lucky enough and I should be able to get it that time.
That one looks like never opened for the package and everything looked clean and brand new. But I found again the misaligned logo of the lens cap again. This time is less, I think in less than 5 degrees to the right when looking from the lens front - so comparing against the first one, the variation is at least 15 degrees. I still accepted that but then I shortly found two big dust particles *inside* this brand new lens (so was the salesman able to see them easily), which should be "included" out of the Pentax lens factory when it is "Assembled in Vietnam". As that was the only new copy at that shop, I gave up finally. After all of the above, I still could not buy the lens and I was upset.
I am really disappointed for the truly inferior and poor QC of Pentax and their Vietnam lens factory once again. I have never seen such problems for Canon lenses of higher grade which were and are made in Japan from my own experiences since I had my first Canon EF lens in 2007. And so did the better Pentax glass when they were made in Japan - I had never seen one bad copy amongst all the Pentax lenses I bought in the whole 80s and 90s. In early 2000s, the only bad copies of lenses which I encountered were those made in Taiwan (I exchanged my FA 24-90 for three times in 2001) and elsewhere which was unknown as the country of origin was intentionally not printed if it was not Made in Japan, for years for the Pentax goods sold in my country.
It seems that the main culprit of the inferior IQ of what the DPR found may also be caused by the poor QC of the Pentax lens factory as actually I found a big difference in IQ when I tested myself. Whilst I do now believe the optical design of the DA 15 should be good enough and is not really that bad, Pentax/Hoya has once lost the opportunity to earn the money of a "new" customer owing to their really inferior production QC. So, this is rather sad afterall.
As for the QC of the Pentax DSLR bodies at the Philippines, it is not good neither from my recent experience. Actually, my K-m Olive was chosen amongst five units at two different shops in Hong Kong, Except one was obviously scratched (which should not be a problem of the factory), the other three has different kinds of misalignment of the RTF closed position and the EV compensation button as well, which was found rotated in a large degree for one unit.
After all, I just wish to ask: WITHOUT better and up-to-standard QC in the Pentax land nowadays , will they survive longer? How can they compete??
P.S. The DPR tested the DA 15 on a K20D, I still do not reject the possibility of that the DA 15 is not working very well as on the K-m, which has a Sony sensor, and so does the K-7, which yet has the Samsung sensor (which has been reported by different users to be problematic).