I bought a used 5D Mark III, and there's one thing I cannot stand about it.

[Holden1]

My previous Canon DSLR was a 40D (which I absolutely loved). It's been a long time coming, but I recently upgraded to a 5D Mark III. The one thing that is driving me crazy about this new camera is the shutter button. On my 40D, there was a discernable detent at half shutter. This is where I would lock focus and recompose, if necessary. The 5D Mark III does not seem to have this detent at all. I can half press, but I have to hold my finger in place with nothing to rest on before pushing down all the way to take the photo.

Is this how they were made, or is my shutter button just worn out, or am I just using this camera wrong?

[Peter]

Reset the camera. Seems like back button focus is activated.

[MikeSowsun]

I have both a 40D and 5D Mk III right now and I see no difference in the shutter button half press or full press functions.

On the 5D Mk III the AF-ON button on the back of the camera is always enabled by default. There are custom functions which change the way the both the shutter button nd AF-ON button works. 

You must either have a custom function enabled, or your shutter button is not working properly. 

[jrhoffman75]

I have neither of those bodies, but two different Canon DSLRs.

Both have a noticable "stop" when pressing the shutter button to meter an focus. Additional force is required to depress fully to actuate the shutter.

Sounds like your 5D shutter button may be defective if you don't feel that "stop" effect.

[ebiggs1]

The 5D Mk III is a wonderful camera.  It is certainly worth sending to Canon for a C&C.  I would do the rest and when that doesn't help call Canon for the C&C. 1 (800) 652-2666