Vier Minolta AF 28-135mm im Vergleich an der A900 - wie gross ist die oft zitierte "sample variation" wirklich? Und wie schlagen sich die 28-135er gegenüber den guten Festbrennweiten im Minolta AF-System? Die folgenden Bilder geben Auskunft. Alle hier gezeigten Ausschnitte sind 100% crops, konvertiert aus Rohdaten der A900 mittels Photoshop CS5 (Schärfung 50, Radius 0.5px, Detail 50).
If someone looks for a high resolution zoom for the Sony A900, the Minolta AF 4-4.5/28-135 mm may be worth a trial. Stopped down to f5.6 or f8, it has the same detail resolution as the best Minolta primes such as the Minolta AF 2/28mm, the 1.5/50mm, the 2/100mm and the 2.8/135mm. In fact, this 25 year old zoom has an equal (at 28 and 35mm) or better (at 50mm and 70mm) corner resolution than the Zeiss ZA 2.8/24-70mm.
I have published several comparing tests both in the internet and in my large book on the full frame Alpha System which document its performance. Some users, however, have complained that my sample "does not represent the average used 28-135mm". I don't know the quality of the "average Minolta 28-135mm", but I know that all seven samples of the 28-135mm I owned had a remarkably consistent performance.
However, be aware that focusing can be tricky - if the 28-135mm is slightly out-of-focus, the detail resolution remains, but the contrast decreases. In addition, the corner performance is strongly affected by a slight misfocusing. I am quite sure that most reported "bad copies" of the 28-135mm simply were slightly out of focus!
I never had more than four 28-135mm at the same time, but I did compare two sets of three and four lenses. Here are the results of my second set of 28-135mm lenses. Even wide open they all have an outstanding detail resolution in the image center. There are no visible differences between the four copies at all. The extreme corners are most susceptible for decentering and other effects of ageing or damage; therefore 100% crops of the extreme corners are shown here as well.
All four lenses (SN 1008346, SN 11301518, SN 16105409, and SN 19103205) were bought recently (2011) here in Switzerland, two of them from a well known shop in Zurich , the two others from private individuals, together with Minolta 7000 cameras. The combination of the Minolta 7000 and the 28-135mm was quite common here among advanced amateurs in the 1980s. Usually the owners cared well for their expensive lens (the 28-135mm was CHF 1090.-- around 1987), and this may explain the good state they are in.
The top row are always 100% crops from the center of the image, the bottom row are 100% crops from the corners.
On the left side "wide open", then the four samples at their "optimal aperture", then - at the right side - the crops from the corresponding prime lens, usually the best in the Minolta AF system.
All images were taken using a Sony A900 DSLR (24 MP). All images were taken with 2s Mirror-Lock-Up (MLU). A professional carbon fiber tripod Giotto 8351B with a three-way-head Manfrotto 410 was used. The RAW data were developped with Photoshop CS4 (sharpening 55, radius 0.5, detail 55). No correction for "Color Aberrations" (CA) was applied!
CLICK ON THE IMAGE TO GET THE FULL SIZE (100%) CROPS!
