Please help: why does the camera keep focusing? and what is DMF?

[Nex Tex]

I was trying to photograph bicycles passing in front of me about 15 feet away. The AF is clearly not fast enough to focus on a bicycle and take the picture before the bike left the frame.

I thought I would prefocus.

I successfully focused (using AF) on a bike, then I turned the camera over in order lock focus by changing it to MF. When I did that, the camera focused on my foot.

Huh???

I didn't press the shutter, it just refocused by itself. I Googled. Yes, the camera is supposed to do that and there is no way to turn it off.

Ok, one option is assign MF/AF to the custom button and change the camera to MF before it has a chance to refocus.

Can DMF also help in this situation? What is DMF anyway?

Here is what the alpha book says:

"After focusing automatically, make fine focus adjustment
manually (Direct Manual Focus)."

Nice, but what does that mean?

 

[Jethro10]

Hi,

DMF does basically what you say. It guesses Autofocus, then you manually focus from there. Supposedly save you time by getting it nearly right to start with.

Normal focusing changes all the time. Because these style of camera are slow at focusing, it does it to try and be more ready when you need it, hence quicker.

If it were me, I'd manually focus on your given point, and then when the bike approaches your give area, I'd shoot in continuous mode, so you have a good chance of getting one in focus.

Jeff

 

[Nex Tex]

Hi,

DMF does basically what you say. It guesses Autofocus, then you manually focus from there.

I am having a hard time understanding what that means in terms of mechanics.

 

[ChangshaNotes]

In DMF you press the shutter part way and the camera focuses, then if you turn the focus ring you get a magnified view and can fine tune your focus. When you stop using the focus ring the view will go back to normal after a delay. It's not really useful for action shots.

 

[davect01]

Ya, great for some stuff, not at all for moving work.

 

[Nex Tex]

In DMF you press the shutter part way and the camera focuses, then if you turn the focus ring you get a magnified view and can fine tune your focus. When you stop using the focus ring the view will go back to normal after a delay. It's not really useful for action shots.

That explains it! btw, it seems that both peaking and MF assist work with DMF (but not AF). Is there any reason not to enable DMF over AF? I can't think of any right now.

 

[dbmiller]

I always set DMF and not AF for that reason. The AF is the same, and if you want to override, you can.

 

[Nex Tex]

dbmiller--here is a wrinkle: for some reason DMF does not allow AF-C, so it's probably not possible (for me) to always use it.