Christine there is no problem to using an empirical approach in everyday photography. You adjust something to get the sort of effect you require. It's when you need to exploit some of these features a deeper understanding of the science is required.
John's question was is it focal lenght or distance ?
Hence all the techno babble to explain it is distance.
I bumped into a similar issue when trying to see if I could increase DOF for a given f-stop by using a shorter focal lenght lens. The problem is if you want to maintain the subject size in the frame you need to move closer and then you end up with exactly the same DOF as before.
So distance and magnification factors come into play with both DOF and perspective.
|