Originally posted by Ex Finn. Pg. 55.
Adjust for sharpest display of information in the viewfinder.
That is the way I do it. Independent of lens, lighting, subject. I focus the digits on the bottom of the display, often after half pressing the shutter to get them to light up.
To mention something new to the thread....
I have four K1x0D cameras. All have the diopter slide one click left of center. This is amazing consistency between cameras and helpful to know. If I knock the slide askew I no longer need to focus, I just set the lever back to 1 notch left of center.
If you find the setting that matches your eyesight then you can make note of it for future resetting.
BTW: My first evening with a DSLR (K100D) I was using an old manual Sigma 70-210 from my K1000 days. I did not realize the slider was bumped toward one end and not knowledgeable to realize it. Of course every photo was blurred!