Originally posted by Talisker I don't know what they are measuring either, but the error bars on the first three measurements at 70mm suggest that that particuar test is worthless...
These bars denote something to the effect of IQ on 30x40cm print on a scale of 1 to 10. 10 is of course considered outstanding.
This is not really an MTF graph as it take into account the sensor, the AF precision and all other camera characteristics.
These graphs are cross comparable between cameras and the best lenses on a !DsMkIII would probably get a 9 mark at the best apertures.
The "error bars" show the dispersion across the frame, the smaller the bars, the better the homogeneity.
The 17-70 shows excellent results until 50mm and a noticeable fall in quality by 70mm. Nevertheless, it also shows considerable CA, noticeable distortion and vignetting.
A good zoom but the recent Pentax primes (200mm, 300mm and 35f2.8 Macro) are showing almost perfect notes on all accounts!