Sat 08-Dec-12 06:20 PM | edited Sat 08-Dec-12 09:39 PM by walk43
With AF Activation (a4) set to OFF it means AF will work with the AF-ON button only hence 'AF-ON only' selected in the menu. In this case the 800 only focuses with the AF-ON button on the back of the camera. If you take your thumb off of the AF-ON button ....still with a4 set to OFF....and move your focus point, then the camera will not focus with the shutter button half-way down but will release the shutter on a full press and record the image.
This is confusing for me because a4 is titled 'AF activation' and 'ON' means the AF-ON button is the only button that will focus and only when it is depressed. If you turn AF Activation to 'OFF' then either the shutter or the AF-ON button will focus the camera.
If I have a4 set to OFF (AF-ON only), then the only focus ability I have is with the AF-ON button.... and I must keep it pressed while I push the shutter button....unless I or my subject do not move at all. (real problem for me doing outdoor macro work with wind, body sway and shallow DOF).
And yes to the one post ....that even if the AF-ON is pressed and focus is not achieved my shutter will release and an out of focus image will be recorded. Personally, when I am taking a picture, I don't always remember or have time to look for the green light as I am frequently looking for the bugs to move or for some other composition issue.
Trap Focus (I know what that is) does not seem to work for me either functionally on the camera or in my preferred shooting process.. so I just forget about it. Maybe, as others have said, it does not work correctly on the 800 or 'AF Lock' fits somewhere in the shooting process ...but I just don't mess with it.
If there is more to this and I am missing something let me know. I still resist using a4 set to 'OFF' and using the AF-ON button because I miss shots due to lost focus. I use AF-S and AF-C set to 'focus' so that I always am assured of a focused image (that's Darrell's useage also I think). I know others use the AF-ON button and it works for them... and wedding shooters have a good use for trap focus, but I have not learned to change my ways and just like the way it works for me. For now...
Dan (Nikon D800,V2,Sony HX400V,Lumix ZS40) "I don't read, I just look at pictures" - Andy Warhol