Pentax-01 Standard Prime 8.5mm f/1.9 (Pentax Q) - Review / Lens Test - Analysis
Lens Reviews - Pentax Q

Distortion

Normally you would expect a standard prime lens to produce next to no distortion. However, this is not exactly true for the Pentax Q lens which shows heavy barrel distortion of 3.3% which will be easily visible in scenes with straight artificial structures.

Vignetting

The Pentax-01 8.5mm f/1.9 shows only a slight amount of vignetting at max. aperture which is hardly objectionable. The issue is gone when stopping down just a tiny bit.

MTF (resolution)

The Pentax Q camera has a very small sensor so you can't expect the same pixel-level sharpness like in other mirrorless or DSLR systems. That said, the Pentax-01 8.5mm f/1.9 makes the most of the given potential here. It is very "sharp" across the image frame even at max. aperture. The peak performance is then reached around f/2.8. The lens is capable to keep the quality at f/4 before diffraction ends the glory at f/5.6 - this is not a problem of the lens but a limitation of the system due to the small sensor size.

Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations

Chromatic Aberrations (CAs)

Surprisingly the Pentax lens is comparatively weak regarding lateral CAs (color shadows at hard contrast transitions towards the image borders). They are clearly visible at large aperture settings but the issue decreases somewhat the more you stop down.




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