I admit I am a gear junkie
Got the 5DSR last week, in my Quixotic search for the best IQ and performance in the smallest package.
Tested it in the backyard against the Pentax. I've posted this elsewhere on another forum, but this is a better place to discuss this.
Obviously this is just a field test, with backyard foliage, brick wall of the garage etc. I tested initially with handheld shots, increasing the ISO to keep the shutter speed constant. I then used a tripod to keep the ISO constant at 100, using MLUP and self timer. Tested from wide open to f16 on both cameras.
Canon 16-35 f4 IS at 35mm and the 24-70 f2.8 MkII at 43mm
Pentax FA 45-85 f4.5 at 45mm and the DFA 55 2.8 prime
I tried to equalize the fov for both cameras.
I was looking for sharpness, resolution, noise and an overall feel for the images. Issues like CA, distortion, center vs edge sharpness etc are obviously lens dependent and would be harder to compare. Still, it was interesting to see if the Pentax lenses hold up against the best Canon has to offer.
Sharpness/resolution: Pentax is clearly better, expected them to be near equal.
Noise: Again, Pentax much cleaner, even in a well exposed image, ISO1600 is about the same as ISO 800 on the Canon. If you have to pull up shadows it gets worse on the Canon rapidly. Again, I expected this.
Overall feel, image look: I know this is subjective but I like the output from the Pentax more. There is a crispness and although the Canon by default saturates the images more, there is a slightly subdued but more appealing quality to the Pentax files, small details are clearer and yet 'smoother'. There is a certain 'muddiness' in the Canon images.
I was very impressed with the performance of the Pentax lenses, particularly the DFA 55 f2.8. It is significantly sharper than the Canon 24-70 especially at the edges at all apertures. Since I was about 40 feet from the subject, I did not see the problems with field curvature etc that others have reported.
Even the much older FA 45-85 (I bought mine used for around $700) is better than the 16-35 f4 IS which is one of Canon's sharpest wide zooms. The Canon is better at the edges wide open, but the Pentax catches up at f8 and remains sharper at the center throughout.
The Pentax is of course a larger package overall, heavier, more expensive (the lenses I have are cheaper than Canon though), has a slower frame rate and the AF is no good for action.
However, if I was looking for the best IQ for landscape work, the Pentax is a better choice despite the limitations.
I wonder how much better it would be given better lenses, esp ultra-wide. The new 28-45 though huge and expensive is said to be very sharp.
I am so much happier with the Pentax that the 5DSR is now up for sale