Depth of field (DoF) is such an odd thing in photography. By setting your depth of field you can create photos that are in focus for huge areas or only millimeters across. I am still trying to grasp DoF. I understand it, but, like exposure, I need to learn what the photograph will look like when I set a certain depth of field.
If you have seen photos where the subject is tack sharp but the background is all blurry that is because of DoF. That blurry background is called bokeh and creates some really cool effects.
One of the keys to remember about DoF is to remember that there are a number of factors that have an effect on it. The first is the aperture that you have your lens set on. The smaller the fstop the smaller the depth of field. That I learned quickly. The second is distance to subject. This factor drove me nuts for weeks. I was using my 60mm macro lens, set at f/2 and I could not understand why my flower pictures were coming out awful. Almost none of the flower was in focus. Then read somewhere about distance to subject effecting DoF. Now it made sense. Since I was so close to the flower my DoF was barely millimeters big.
I know this but I don’t ‘know’ it in my head intuitively as of yet. I took a picture recently at work of a pumpkin display by setting my aperture pretty low as it was indoor lighting. When I reviewed it later I realized my mistake. The center item was in focus, but the pumpkins around the edges were way out of focus. They had been set in a semi-circle so were outside the DoF I had set. Even though my DoF wasn’t tiny it was still not large enough for what I shot. Basic mistake.
I should have done three things:
- Used my flash
- Set my DoF higher
- Focused on one of the outside pumpkins, locked my focus and recomposed the shot.
This just emphasized that I need to sit down and test my camera to find out what it does in what circumstances. Hopefully it will help me find the sweet spot of each lens, where the ISO setting gets really noisy and the distance to subject/aperture settings.
Here is an example of a picture I took last year that has some good bokeh.