My frustration level is at its peak right now!

[Richard Lane]

Hi Anri,


Here is an example. If you are using a supertelephoto lens, then your lens can become very far out of focus, by trying to focus search on something that it does not see. If this happens then your lens may not recover in time, to get the shot.


There is a custom setting known as Lens drive when AF is impossible, this custom function may be found in C.Fn III-4 on the 7D. I'm not sure where it is on the 50d.


Lets say that you have "focus search on", and you are tracking a bird in flight with a blue sky and then you temporarily lose the bird in the frame, now the lens has nothing to focus on, therefore it will continue to search for something to focus on, and in doing so it may become further and further out of the focusing range that you were working in, especially with a long telephoto lens. Now, if you re-acquire your focusing target (lets say the bird for instance) the lens will now have to focus search a second time to re-lock on the target. So, it can take a while to focus search (looking for the subject) out of the target range initially, and then focus search again to reacquire the target.


Now, lets say that you have "focus search off" and you temporarily lose the bird in your frame, now the lens will not get way out of focusing range while trying to focus search on what it doesn't see (because focus search is off), so now when you re-acquire the bird in the frame, the lens shouldn't be that far out of focus, and therefore it should re-focus on the target faster, because it wasn't hunting and it didn't drift that far of the subject distance range. So, in theory it will re-acquire the target faster.


The other way the photographer can re-acquire the subject faster with "focus search turned off " (thereby limiting the out of focus range) is by using the manual focus ring to re-establish the subject, without the lens having to focus search and move all of that glass backwards and then forwards with the AF motor, which is not as fast as the manual focus ring.


In sports, we can also use the metal prefocus-ring on the super-telephoto lenses, to quickly reacquire our target distance, without focus search doing it's own thing.





Rich

[JJphoto]

Very useful information here, thanks Rich and elmo!

[Richard Lane]

Thanks Guys!

[Bill W]

RE: Lens drive


Thanks Rich......I've experienced this "frustration".


Bill