| Minolta AF 20mm 1:2.8 (22) |
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The Minolta 2.8/20mm is the last of a series of 20mm / 21mm lenses made by Minolta. If we just count the retrofocus constructions we will find three optical designs: the extremely well built MC 2.8/21mm (12 lenses, 510g, 72mm filters; 1971-1976), the much smaller MD 2.8/20mm (10 lenses, 240g, 55mm filters; 1977-???), and finally the AF 2.8/20mm (10 lenses, 285g, 72 mm filters; 1986-...). The current Sony 2.8/20mm is virtually identical to the Minolta AF 2.8/20mm. The big and heavy MC 2.8/21mm is still regarded as one of the best superwides, with a performance close to the legendary Zeiss / Contax Distagon 2.8/21mm. The 2.8/20mm is slightly heavier than its MD precedessor, but still quite lightweight. Along with a 72mm filter diameter the lens has a “rear element focusing” for fast AF. The mechanical quality is excellent (fully metal, even the focusing ring!). Along with AF 1.4/50mm, the 2.8/100mm Macro and the 2.8/200mm APO this lens was part of my original lens line-up for the Minolta film SLRs such as the 9000, the 9xi, and the Dynax 9. Probably 40% of my landscape photos – usually using Fuji Velvia or the high-resolution Kodak Technical Pan TO 2415 – were taken with this lens. For very good results one should stop down to at least f5.6, better to f8 or f11. The lens has a visible wave-like distortion which is difficult to correct by postprocessing. Using the Minolta 2.8/20mm on APS-C DSLRs was never entirely satisfying. The image corresponds to a “boring” 30mm FF lens. And the image quality was not what I had experienced in analogue days: wide open the detail resolution was OK, but the contrast was very low; at f 5.6, surprisingly, the detail resolution was worse, even though the contrast is OK. And stopping down to f11 resulted in strong halo-like blooming. Similar experiences were made by many others. When the a900 arrived I (and many others) was surprised to re-discover the original qualities of the lens. I found that three different causes were contributing to the problems i had experienced on APS-C-DSLRs: 1) The 2.8/20mm is a spherical lens design, and the residual spherical aberrations generate a visible focus shift when stopping down from f2.8 to f5.6 or f8: the focal plane “travels” towards infinity. To correct this, one should focus by AF and then turn the focus ring manually to a closer distance (about 1mm at f5.6). Alternatively one may use the “Micro-AF” adjustment of the a900 to ensure proper focusing at f5.6 (about -5 on my a900). This clearly increases the detail resolution. 2) My 2.8/20mm could not be focused to infinity (many of my first-generation Minolta AF lenses have the same issue). By removing the thinnest shim from my 2.8/20mm it was re-adjusted to infinity; especially landscapes became visibly sharper. 3) In addition I found the lens protection barrel on the rear side of my 2.8/20mm to be slightly de-formed. As a result the rear lens itself got scratched slightly, which in turn caused strong blooming at small apertures (f8 ... f16). Replacing the rear lens and the lens protection barrel solved the problem. After this maintainance the 20 years old 2.8/20mm was as good as I knew it was originally on film. On the a900 this lens is a hidden gem, especially when used for landscape or street photography. At f8 neither the Minolta 3.5/17-35mm G nor the Zeiss Vario Sonnar ZA 2.8/16-35mm reaches its corner detail resolution. The contrast however – as mentioned above – is rather low between f2.8 and f5.6, gradually increasing from the center and reaching perfect corner levels at f11. These characteristics are typical for many Minolta primes (especially for the 2.8/20mm, the 1.4/35mm, the 1.4/50mm, and the 1.4/85mm), and quite useful on high-res digital sensors: the missing micro-contrast of Minolta lenses can be easily improved by PP. The missing detail resolution of other brands, however, can not be reconstructed by Photoshop. Below there are some Sony alpha 900 test shots using my Minolta AF 2.8/20mm which I bought in 1987. The RAW files were converted using Photoshop / Camera Raw 4.6 beta. "Sharpening" was set to 50, the "Radius" to 0.5 pixels, and "Detail" to 50. No correction for chromatic aberrations was applied.
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