I decided to put the A2 head to head with the Alpha 550 and top grade glass, and size both images as if for Alamy (5120 pixels on the longest side, exported using Adobe Camera Raw). This is a very unfair test to the A2, which is trying to pull 19.7 megapixels out of 8 while the A550 is only needing to go to 17.5 megapixels from an original 14.2. I used a tripod, and set both cameras to their minimum ISO (64 for A2, 200 for A550). The 2-second self timer was used in both cases, with Live View on the rear screen. Here, the 920,000 pixel screen of the A550 is just exceptional with the Quick Live View; it's a different class entirely to the A300-380 models.
The A2 was set to f/11 for maximum depth of field. This is well past the diffraction limit of the sensor, which actually gives the best sharpness wide open. The 7.2-50.6mm Konica Minolta GT f/2.8-3.5 lens is pretty good wide open too. In practice, it's best to shoot around f/4 to f/5.6 with the A2 when subject depth permits. For this shot, I wanted maximum depth of field as earlier hand-held attempts at wider apertures had not been in focus for entire clumps of toadstools.
The A550 with 16-80mm CZ was set to f/16 - again, this is beyond the diffraction optimum, which is about f/8 with the 14.2 megapixel sensor. The same reasoning applied. To 'handicap' the A550 to match the A2 and similarly extend the depth of field, I should have set f/22 or even f/32 but the CZ lens doesn't go beyond f/29 even at 80mm. Just as well, there would be little point in using glass of this quality and then losing the sharpness.
Both images were processed using ACR 5.5 (the A550 first converted to DNG via Lightroom 3 Beta) and in both cases identical settings were used. White Balance was preset to Daylight and the cameras reported slightly different settings for this. Medium Contrast tone curve was used, but Auto was applied, which balanced the brightness and contrast, with black point reset to zero. No lens/CA correctin was applied. The Detail menu was set to Sharpening 25, Radius 1.0, Detail 10, Masking 0, Luminance NR zero, Chroma NR 25. No further noise reduction or any processing was done to the files.
Original A550 shot: http://www.pbase.com/davidkilpatrick/image/119016495
Original A2 shot: http://www.pbase.com/davidkilpatrick/image/119016567
In both cases, you can open the full size image at pBase and also see the EXIF data.
Of course the 14.2 megapixel camera is better than the A2. But the A2 is well up to the standard required for Alamy and much better than a typical 6 megapixel DSLR shot taken to this size. Please feel free to post a link to this on any forums I can't reach!
David
