The only trusted source I rely on is myself and my cheap under $100 lenses (18-55kit, 70-300-Sigma, 35-105 film legacy Pentax) on my 2006 Pentax K100D DSLR.
With post processing software diffraction at f/16 or no diffraction at f/8 I still get sharp and in focus Raw images. I just have longer DOF shooting f/16.
As a strictly f/8 shooter for over 6 years both outdoor/indoor I've recently discovered f/16 even with my kit lens gives me just as good a shot as f/8 whether it's sunny or indoor dim lighting. I just have to create a custom point curve along with the right amount of clarity in CS5 "and I'm there".