Many Canon DSLR / mirrorless cameras have an option to choose whether the camera searches for focus if it cannot find focus. Especially on long lenses with no focus limiter, the lens can become grossly out of focus. Furthermore, the focus search seems to be slow, the slower the longer the lens is.
Typically, if you are using a short lens, and are not taking macro photographs, the focus from the last picture should be a good initial guess for the next picture. Especially these short lenses don't have a lot of background blur, so it is not likely that the objects at the desired distance would be just blur in the viewfinder.
For long lenses, you want to use focus limiter and turn off the "continue focus search" option because the search is so slow and because the lens can become grossly out of focus.
About the only thing where the "continue focus search" option on short lenses matters is if you have nothing to focus on near the focus point. Then the lens can needlessly scan through the whole focus range, meaning it becomes out of focus and taking the next picture is delayed then.
So, my opinion is that the "continue focus search" option should typically be turned off because:
- On short lenses, the last focus is good enough initial guess and it avoids unnecessary delays when trying to focus on something that lacks edges to focus on
- On long lenses, the focus search is very slow, the lens can become grossly out of focus, so it's better to set the initial guess manually by turning the focusing ring and then let the autofocus do the rest
Is there any benefit of the "continue focus search" option in real use? My experience is that it should be typically turned off no matter what the situation is.
Let's limit the answers to phase detection autofocus and/or dual pixel autofocus. I understand that with contrast detection autofocus only, the situation might be such that searching for focus is necessary.