OK, I've got two more sleeps till my new Sigma 150-600 Sport arrives and my brain has gone into overdrive, or maybe melt-down, about using it.

I'm particularly thinking about the narrow DOF. Picture a scenario where that seldom seen birdie lands on a branch about 10m away in fair light. After a couple of test shots you've already got your camera set at say ISO1000, 1/1000sec and f11 when about 20cm of Whipbird lands on the branch in a half face-on pose. These settings are of course flexible.

Focus on the eye, click, gotcha ! Examination of the shot reveals a sharp head, shoulder and upper back, the rest an increasing blur toward the tail.

Checking online DOF charts shows the following:

DOF Snip.JPG

At these settings you are only going to get half the bird in sharpish focus. That 12cm DOF is split evenly, half in front of your focus point (the eye) and half behind it, so almost half your area of sharp focus is wasted on vacant space.

So, what if you had an in-camera setting with a deliberate 5cm of back focus, which in theory should give you that amount of extra sharpness behind your focus point ?
This of course would only work with a co-operative subject, ie one that stays for longer than about 20 seconds to enable you to pull up that setting in your menu.

Am I going nuts? I think I need a cuppa and a lie down.