I mentioned in a “About Zoom lenses – Pt1” a discussion at DPreview forums regarding depth of field and how zoom users in particular would go about determining how to approach the subject.
For most people reading through the various comments it would seem that no one seemed to have a particularly good grasp of the process. The keyboard warriors among them sallied forth with more math’s than I can remember from my science and physics classes.
All of it, and I reiterate this, ALL OF IT IS A LOAD OF RUBBISH !! AND REALLY HAS NO BEARING ON 99.9% OF OCASSIONS FOR THE AVERAGE CAMERA USER.
So what do I mean by this? Well its pretty clear that the vast majority of people replying to the question on the forum have vastly different interpretations to the meaning of depth of field and how to calculate this. Especially when applying to zoom lenses.
If I’m shooting wildlife, action sports, rodeo for example I wont be worrying about depth of field. What I will be concentrating on is the action. How the subject looks in the viewfinder, composition, where I am in relation to the subject, and lighting.
Worrying about what might be in or out of focus in the background or foreground is largely immaterial.
If I have the luxury of having my camera on a tripod and my subject matter is fixed or only moves at the speed of an arthritic turtle then I will be more likely to consider fore & background elements at what should be in focus.
To better understand this process I have included the link below to Photography Online‘s latest episode. For me at least this YouTube Channel is by far the best photography program I have watched and I’ve watched hundreds of photography channels, and no I have no affiliation with them, although my family does live on the Isle of Skye.
In this episode there are two outstanding sections that deal with lenses and how to use depth of field for your images. The first part starts at 0.53 seconds and the second section that deals with DOF and selecting aperture and starts at 18.26 minutes. Don’t let the topic headings put you off. Watch the video, in fact watch the whole program its more than worth it.
In the second link below Marcus shows how the various parts that make up focal length actually relate to each other. This is another really good demonstration in practical terms. It also demonstrates one of the misunderstandings when people talk about DOF, typically confusing DOF with perspective. The section about lenses in the second video starts at 1:30.