I recently received an email from David, who has some questions about depth of field:
As you have a lot of experience of using the Fuji X-E1, may I please ask you for some advice regarding landscape focusing.
My aim is to use the 18-55mm kit lens with the majority of shots taken at the widest end. I have in mind setting the lens at Hyperfocal distances, based on a crop factor of 1.5 and a circle of confusion of 0.02. I think the first figure is reliable, but I’m not sure about the second in relation to the X-E1 – perhaps you could confirm.
I have already done some testing at home using the attached table (which come from the well respected DOFmaster site).
In my experiment I carefully measured distances at apertures of f8 and f11 using a tripod and a printed card as the subject. I set the lens manually at the hyperfocal distance, using the EVF distance scale. I was disappointed to find that the closest point of focus was not as sharp as I had hoped. Have you any idea why this may be?
I did a further test on aperture f11 and this time set the distance scale at 4 feet (2/3 of the way between 3 and 5 feet). This resulted in a sharp image from 3.5 feet. This would suggest that the distance scale is not accurate.
Any suggestions you have to overcome the problem would be much appreciated.
Let me preface my response on the depth of field (DOF) issue by congratulating you for taking the time to conduct your own experiments. One of the great things about digital cameras is that we don’t have to trust what we read — we can easily and quickly conduct the experiments ourselves. In addition to getting the answer to the question at hand, we end up knowing our gear at a much deeper and even intuitive level, which is extremely important when we are in the field and we don’t have time to ponder and calculate, but must instead make a photograph in the moment.
The rest of this post is going to be somewhat involved, so let me share a quick thought right at the beginning:
The usefulness of DOF calculators is very limited, as they are based on subjective assumptions that may not match what you are doing with your photographs. The best way to align your expectations with exposure choices is to test them yourself and evaluate images in the form that you most often produce — and not just at 100% magnification on a computer screen.
What is DOF? Essentially the depth of field is the distance range in front of and behind (unless you focus at infinity) the focus point within which subjects are likely to sharp enough to seem in focus when the photograph is viewed at some arbitrary magnification. This size of this range increases as we stop down (for example, going from f/2.8 to f/8 expands the DOF) and decreases as we open the aperture (going from f/8 to f/2.8 contracts DOF). This is a source of creative control for the photographer. A smaller aperture can allow subjects across a greater distance range to appear relatively sharp, while a larger aperture can keep the primary subject in focus while pleasingly “un-focusing” elements in front of and behind the primary focus point. Continue reading Reader Question: About Depth of Field