Manual Focus and Override

niranjan · Sep 28, 2011

As i have switched to DSLR very recently , i m not getting my Camera work for me as i wish. I have been using the FILM SLR for so many years and the total MANUAL control is what i m used to. Aperture changes directly on the dial and the focus CIRCLE inside lens gives accurate FOCUS every time.

I m little confused with this new concept Autofocus with manual override. I wish to know how the complete MANUAL FOCUS mode is different from AF with manual override. (means why not go totally manual than Override option?)

Tomasko · Sep 28, 2011

Manual focus is manual focus.. You turn the focusing ring and that's it.
AF with manual override is simply autofocus with the option to override the focus after the lens has focused. AF isn't perfect, so slight modifications are sometimes needed to get it right.

Just don't forget, that with many lenses you shouldn't override AF, because you can damage its mechanism. The description on the lens should read "full-time manual".

TiCoyote · Sep 28, 2011

If you had an old 35mm SLR with a prism, your viewfinder was BIG and BRIGHT and easy to focus. If you have a DSLR with a prism, or even worse, a penta-mirror, you will find that the view is smaller, darker, and harder to focus. You have to be pretty slick to focus manually faster than the AF. Play around with the AF points.

Overread · Sep 28, 2011

AF with manual override means that you can use the AF to get a lock onto a subject and then you can manually make adjustments to that focus to perfect it. It generally means working with focus and recompose - where you use an AF point to focus on the subject (typically the middle point) and then recompose the photo for the final composition; which likely shifts the plane of focus, thus needing the manual override to make a slight adjustment, without having to hunt for the AF/MF switch on the lens itself (which can be a pain if your lens has more than one switch).
As said above though, experiment with the outer AF points as well (typically you want AF set to a single point, rather than all points being active) though the speed of them will vary, on entry level DSLRs they are weaker, whilst the middle point is the strongest - on midrange and upper level bodies the number of AF points increases and the outer points are also stronger/faster AF sensors as well.

It also works well if you combine it with backbutton AF control; whereby autofocus is not engaged by a halfpress of the shutter button, but by a press of a button on the back of the DSLR. This mean that you can use an AF mode which supports continuous AF (ie all the time you hold the button down the camera constantly checks and focuses, good for moving subjects) and if the AF is failing you just lift the finger from the backbutton and shift to manual focus instantly (no hunting for the AF/MF switch) and when you press the shutter fully the AF won't kick in and try to refocus again (thus letting you take the photo).

Combined with AF and MF the manual focus override/fulltime manual focus lenses are a very powerful tool and certainly capable of a lot. Learning AF will be important as the modern DSLR is made with the intent of AF being used; rather than the older manual focus cameras where manual focus aids and a brighter viewfinder were the norm since it was all manually driven.

As an additional point regarding AF remember that AF works by finding the closest point it can to the camera (under the AF point(s) which are active) where it can detect a contrast difference in the scene. Thus if you try testing on a pure white wall/blue sky or any other scene where there is no or very little contrast change then the AF can fail; another good example is foreground elements, eg if you are ever at the zoo and try taking a photo of the big cats, where there is typically a wire cage at a distance between you and the cats the AF can end up locking onto the wire rather than the cat (even though fully focused on the cat the wire blurrs out).
(ps big cats are a good example as often there are 2 barriers so that you can't put the lens right up to the wire to eliminate this problem).

niranjan · Sep 30, 2011

Ok. That gave quite an idea...

but the AF and MF are Camera Functions or Lens Functions ? as i read the above post from "Overread" i checked with the lens i got and found no such SWITCH on the lens.( i m trying my hand on Sony A200, having small AF-MF switch on the camera body itself.)