Digital Focusing Part One

By: Gary Ferguson
In many respects focusing in the digital era is no different to focusing in the daguerreotype era or in the Tri-X era. The same optical laws apply and the things we choose to photograph, people and places in the main, are also pretty much unchanged. So why should we need a reappraisal of focusing guidelines and focusing techniques?
Two reasons.
Firstly we’re tending to make bigger prints from sensors that are smaller than traditional negatives, so greater enlargements mean the focusing challenge is more demanding than ever before. And secondly there are now digital tools available that, for some shots at least, can significantly change the realities of focusing.
The basis of practical photographic focusing is the concept of a “depth of field”, a zone of acceptable quality that lies either side of a plane of sharp focus, and which extends or shrinks as you stop down or open up the aperture. If you’re unclear about this there’s a good “depth of field primer” available ...