It is sharpest at the following apertures: at 18 mm - from F / 5.6 to F11, but a little sharper at F / 8; at 24 mm - from F / 8 to F / 11; at 35 mm from F / 5.6 to F11, at F8 - excellent; 55 mm is not bad from F / 8 to F / 11. In general, the sharpness and contrast in the pictures very much depends on the weather conditions, the state of the air, if it rained, the wind blew away the smog, the sky is clear, there are separate whitest clouds in the bright blue sky, and even a day off, never be lazy, take your camera and go out to shoot , at the focal lengths and corresponding apertures that I have given, you will get very sharp pictures, especially at 35 mm at f / 8. But if you want even sharper, then shoot in RAW and at least minimally process it in the lightroom program (there are special sliders). Sharpness (and contrast) also depends on where the sun is, for example, if the sun illuminates you from the side, that is, the shadow falls from you either to the left or to the right, then be sure to screw on the polarizing filter, there is a special hatch on the hood of this lens, move cover with your finger, and through the open hatch with your finger, slowly begin to rotate the ring until the picture becomes the most contrasting. I compared it with the TAMRON 17-50 and I can say that the PENTAX 18-55, under some equal conditions, will in no way be inferior to the tamron, especially by 35 mm at f / 8.