for nikon d90 users

[ghache]

I am not sure what other models have this feature but this discussion was based on the D90.

really interesting technique called the Focus trap using the AE/AF Lock button funtions.

Flickr: Discussing A few focusing thoughts... in Nikon D90

 

[myfotoguy]

That's good info. Some other cameras have an "AF-ON" button (D300 for example) that allows you to focus similarly. It allows you to use the AF-ON as the focus mechanism and still use the AE/AF-L buton for exposure lock if you choose.