Here are 4X enlargements of the right upper corner of original pictures of Quebec City taken from the tip of Isle d'Orleans, 10 kilometers away. The lens was set at 105 mm FL, then shot successively @ f/8, f/11 and f/16. A slight bluish "marine layer", due to considerable water evaporation, is visible troughout the images. The first picture taken @ f/8 shows the most far-away details, diffraction softening the intricate details a little more @ f/11 and even more @ f/16. We can see flags atop a few buildings here and there, demonstrating the awesome capacity of the K3 III sensor's coupled to this DFA 28-105 mm HD zoom at gathering far-away information. All the images were given the exact same Post-processing so as not to introduce unwanted variations in rendering.

CONCLUSION : f/8 should be used as often as possible, f/11 is a nice second choice, f/16 should be used only when extensive depth-of-field is needed.

[MikeNArk]

That seems to be a very rational conclusion. This lens gives good results on the K-3III.

[angkymac]

Somehow my eyes are seeing, at f:11 a slightly sharper steeple with a cross(?) on top at the very far right.
Yet, those flag-poles or antennas in the center of this enlargement does seem a bit better at f:8.
Regardless, the resolution is phenomenally good at either aperture.
I had no idea that 28-105 could be that sharp!
Angky.

[RICHARD L.]

THX !

Using f/11 with the Pentax K1 + DFA 28-105 mm HD has been my "Modus Operandi" for the last three years with great success. On the K3 III, the pitches of the sensor's grid are smaller and diffraction thus may appear sooner, even at f/11. So from now on for a while, I'll have to take pictures both at f/8 and at f/11 and make my mind as to which produces the most pleasant images with the K3 III. Getting to know the quirks of a particular camera body takes time.

Regards