ISO performance: Pentax K20D vs Sony Alpha A550

Took a few shots today comparing two very different cameras with two very similar lenses: the Pentax K20D + Pentax FA 50 f/1.4 lens, on the one hand, and the Sony Alpha A550 + Sony DT 50 f/1.8, on the other. In the following table, the first shot was taken by the Pentax K20D and processed in Adobe Lightroom 3.2. The second shot was taken with the Sony A550 and processed in Lightroom 3.2; the third shot is actually the same A550 raw file, but processed (using default settings) in DxO Optics Pro 6.2.

Pentax K20D

Sony A550, processed in Lightroom 3.2
Sony A550, processed in DxO Optics Pro 6

You can see the entire, hugely boring gallery of test shots here, if you are really interested.

I have a couple observations.

  1. It’s really quite remarkable how well both of these cameras performed at the higher ISOs.
  2. With the same exposure settings (that is, same ISO, same aperture and same shutter speed) the Pentax K20D generates a photo that is consistently darker than the Sony A550. In itself, this is neither bad nor good. However, if I boosted the exposure or brightness of the K20D photos in order to match the Sony photos, it’s likely that noise would be boosted as well.
  3. DxO Optics Pro makes a difference, or at least seems to. The default conversion done by DxO for the DT 50 f/1.8 SAM lens + A550 body (#3 above) is a little better exposed and also cleaner and sharper than the conversion done by Lightroom 3.2 (#2 above). Now, I didn’t tweak anything in Lightroom here, and perhaps with just a few clicks, I could get the image in Lightroom to look like the one in DxO. Haven’t made my mind up yet about that.

Bottom line: In low-light, the A550 performs as well as or better than the Pentax K20D. The A550 is just one year old, and the K20D is now over two years old. The not-yet released Pentax K-5 can be expected to do much better; but it also costs three times as much as the A550. And the performance of the K-5 will probably be matched by the Sony A580, which is due out shortly after the K-5.

No clear winner here, but I was looking more to see if there would be a clear loser—and there wasn’t.


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