Critical Focusing Example

In a previous thread, I stressed (again :p ) the benefits of manually focusing. Nature being as chaotic as it is, often there is just too many things in the viewfinder that Auto Focus can get hung up on.

I also mentioned focusing into the subject from both the front and rear. This is because when the subject is small in the viewfinder and not in the center, critical focus is tough to see (especially in a darkened environment) and it is not readily apparent exactly when the target "popped" into focus. Focusing from both sides (if there is enough time to accomplish) maximizes the possibility that you got the critical focus exactly right.

Here is a personal example from this morning. These three are from 4 consecutive exposures just seconds apart with a 300mm. First image is a full frame example. You can't move the focus ring with enough precision to correct either rear or front focus problems. You got to shoot what you think is in correct focus, then intentionally move the focus way off, then try again, and again.

Loupey, when you say "rear focus," do you mean an object directly behind your subject, or the farthest part of your subject (couldn't think of the right word)? Same question for "front focus?"

In textbooks, the terms "front focus" and "rear focus" means something else - I think.

I simply refer to front focus as any plane of focus which is closer than the exact spot I was aiming for. Similar and reverse for rear focus.

For example, on a frame-filling shot of a bird, If the focus is just short of the eye but the chest is in focus, I consider it a throw-away and my reason for it would be front focus.

In the past, with my old Konica that only had manual focus, when grabbing a quick shot, I would almost always settle for a front focus shot first - with the rationale that at least some of the subject was likely to be in focus, with DOF increasing exponentially behind the point of focus. I still use that sometimes, even if the subject is completely still, and I can't see well enough to get the exact point that I want in focus (more and more common the older I get).

Interesting that in your example, Loupey, that the deer was clearer in the rear focus than in front focus. I guess it all depends on how close or distant your points are relative to the subject. I know that I would have had a lot of difficulty getting the deer in clear focus being that far away. My eyes just don't do detail anymore. Gotta save up for that laser surgery - hmmm - since my photography is a business expense due to all of the photos I take for the job, maybe my laser surgery could count as well?? Hmmmm.