How to Use "Trap Focus"

[Steve S]

I have a canon 40D, is there a way to set it up for trap focus? I can focus with live view, but that takes too long on some subjects.

[Jim B.]

Hi Steve,

A technique I hadn't heard of until now.I did a search and came up with this:
http://www.phototakers.com/forum/ftopic61804.html

[aertaylor]

I just tried 'trap focus' on my Samsung GX-20.
It works! - now I'll have to manufacture an occasion to use it!

[Steve S]

I can't figure out how to set up my 40d. I don't think it will work with this camea. If you hold down the shutter button 1/2 way, the focus light will light up when it is in focus though.(something i didn't know it would do). This will work for what i want to do. When i use the 2x or 1.4x +2x converters, i loose auto focus. Now all i have to do is look for the focus light in the viewfinder and i'm good to go.

If anyone knows if the 40d will work with trap focus, please let me know.

[Colin Southern]

I prefer "snap focus" where I 1/2 depress the shutter release - it focuses in a "snap" - and then I can take the shot

[Radu Dinu Cordeanu]

Hi,
My handbook tells about without this name.I choose to press the shutter button halfway.
Regards.
Radu Dinu

[David]

Steve S - A quick google of trap focus for Canon DSLR's strongly suggests that it cannot be done. However this link describes a possibility if you have a particular type of lens:

http://eosdoc.com/manuals/?q=ATrapFocus

The trick appears to be to fool the camera/lens into thinking it cannot focus.

Not really much help, but perhaps Canon will build trap focus in in later models.

David

[Dave Humphries]

Hi all Nikon shooters,

I have tried this indoors and it works on the D5000
(and almost certainly will on D3000, D90 and earlier).

For D3/5000:
1) Call up Menu
2) Use 4 way cursor pad to navigate to Custom Setting Menu (the Pencil)
3) Choose f "Controls" and OK
4) Go down one to f2 "Assign AF-L/AE-L button" and OK
5) Scroll down to bottom option "AF-ON" and OK again

The effect this has:
The half pressing the shutter button no longer causes AF
Only using the "AE-L, AF-L" button does this now

To use:
Frame up to put your selected focus point on something at the required focus distance
Use your thumb to hold down the "AE-L, AF-L" button to trigger AF and wait for the 'peep-peep', then release thumb
Now compose the shot
Fully depress the shutter button (nothing will happen)
When the subject to reaches the plane of focus, the camera starts taking sharp pictures (in theory)

Of course, it could be a good way to miss a shot, but it seems to work OK at the telephoto end of the lens range (70mm and greater).

If I focused on something, then panned around the room with the shutter button down, nothing happened until I went back to what I had focused on, or something at the same distance, then it burst into life.

When you want to restore normal AF function on the shutter button, repeat steps 1) - 4), but obviously change step 5) to select away from AF-ON e.g. to whatever you normally have set there.

Thanks for the info. Steve and Jim.

Must try it for real

[Steve S]

Hi all Nikon shooters,

I have tried this indoors and it works on the D5000
(and almost certainly will on D3000, D90 and earlier).

For D3/5000:
1) Call up Menu
2) Use 4 way cursor pad to navigate to Custom Setting Menu (the Pencil)
3) Choose f "Controls" and OK
4) Go down one to f2 "Assign AF-L/AE-L button" and OK
5) Scroll down to bottom option "AF-ON" and OK again

The effect this has:
The half pressing the shutter button no longer causes AF
Only using the "AE-L, AF-L" button does this now

To use:
Frame up to put your selected focus point on something at the required focus distance
Use your thumb to hold down the "AE-L, AF-L" button to trigger AF and wait for the 'peep-peep', then release thumb
Now compose the shot
Fully depress the shutter button (nothing will happen)
When the subject to reaches the plane of focus, the camera starts taking sharp pictures (in theory)

Of course, it could be a good way to miss a shot, but it seems to work OK at the telephoto end of the lens range (70mm and greater).

If I focused on something, then panned around the room with the shutter button down, nothing happened until I went back to what I had focused on, or something at the same distance, then it burst into life.

When you want to restore normal AF function on the shutter button, repeat steps 1) - 4), but obviously change step 5) to select away from AF-ON e.g. to whatever you normally have set there.

Thanks for the info. Steve and Jim.

Must try it for real

It also works for manual focus. press the shutter button and then focus very slow and when focus is achieved , it will fire. Which is what i wanted to do, but can't because it won't work with canon