Focus Stacking
Sometime we need a large file size and all the image to be in focus but the physics of the lens and camera used dictate that we can't get it all in focus with one shot.
This is when we need to Focus Stack; we take several images of the subject, each one shot at a slightly different predetermined focus and 'stack' (merge) them together using a cleaver bit of software called Helicon Focus.
Have a look at the video below to see the process.

