#174. "RE: Testing of D800 with Reikan's FoCal application" In response to In response to 168
Sure Clint we were all taught this back in the day: "I was taught that once focused on a spot, abut 1/3 of the area in front of and 2/3 behind the focused spot would be the depth of field. But I don't see people setting up their focus points that way and not sure if it is taken into consideration into the software programs."
HOWEVER if you run a DOF app or any of the online DOF calculators you will find this 1/3 2/3 "rule of thumb" is rarely the case. I believe the front/back focus zone ratio varies by focal length and subject distance and appears to be most commonly 50/50. Certainly Lens Align guidance is to AF fine tune on a 50/50 basis. I believe you can find this topic on the Lens Align website. Len Align also has a calculator on their site, for use in calculating the distance to tune a given focal length.
Anyhow based on what I've come across in the last few years, I believe that old 1/3 2/3 rule is best left back with the film days
Having said all that, I have sometimes been tempted to bias my fine tuning such that the additional DOF is mostly behind my selected AF point. For example in Theatre, that might work very well for me. But for portrait it would be distracting I think if the subjects nose became out of focus. Maybe for portrait a 2/3 1/3 strategy (i.e. reverse the old rule) could be effective. Tough one to decide and overall a tough subject to wade into