Focus trap

[Javelin]

I read about this method but the details of it didn't soak in because I thought I would be able to do this with my A700 but now I'm not so sure. This was described as focusing on a point a measured distance awayturning manual focus on and recomposing. then holding the shutter down and when something goes in front of the lens at the same measured distance the focus lock fires the shutter. will this work? or is this a feature on another camera thats built in?

[rogprov]

I expect some camera has this facility - but not the a700. I remember, a long time ago, having a Yashica AF230 film SLR which could do this trick

[David Kilpatrick]

It tends to be a feature of camera which focus on the sensor itself - consumer digital cams. In theory, the A700 will do it; you just set the menu to 'Focus Priority' instead of 'Release Priority' (I have mine set that way all the time), select continuous focus, and following a subject while keeping the shutter pressed. What it will not do is trigger the shutter when only AF is activated, and that is what you want.

An alternative for wildlife work is to use the Zigview R series video attachment. It can be set to fire the shutter when an object enters the frame. In my experience, the lag is just too long and the sensitivity either shoots when a shadow changes in the light or a branch waves in the wind - or fails to notice the animal entering the frame!

David

[Javelin]

Damn. I knew this. in fact I already do this and it works quite well. at first it was a little frustrating with a fast moving (in more than one plane) object because sometimes it just can't focus (this was the A200) but when it does the shutter does go off and you get a nice charpp image. I just didn't put 2 & 2 togehter when I was reading about "focus trap" which seems less usefull to me now

. In theory, the A700 will do it; you just set the menu to 'Focus Priority' instead of 'Release Priority' (I have mine set that way all the time), select continuous focus, and following a subject while keeping the shutter pressed. David