SLR Geek

How do you know which lens will give you the most control over DOF and the smallest DOF if you don’t have a DOF field calculator with you? Much like in my article on Bokeh the lens focal length divided by the wider the aperture opens divided by the minimum focus distance and hence closer you are to the subject the more possible control you have over DOF and the thinner a slice of DOF you can get. So this means most longer focal length lenses and all macro lenses give you a lot of DOF control.

The focal length to maximum aperture is easily obtained by simply dividing the focal length by aperture. For instance, the ratio of a Canon 85mm F/1.2 II L lens which is an extreme DOF lens when shot wide open would be 85 divided by 1.2 giving you a ratio of 70.8. On the other extreme is the Canon 15mm F/2.8 fisheye. This lens produces the most DOF but at the same time gives you almost no control over it. Dividing 15 by 2.8 only gives you 5.3 when shot wide open meaning everything is in focus. The higher the number the more control over DOF that lens can produce. Lenses with a ratio of 100 such as the Canon 200mm F/2 IS L lens are capable of producing an extremely narrow DOF.

A lens can be stopped down giving a whole range of numbers and a whole range of DOF but for the purposes of this comparison we are hunting for the minimum DOF area of a lens so you always run the fastest aperture and the longest focal length in your equation if it’s a zoom. But what about the minimum focus distance you say? Haven’t forgotten you. Let’s take the 200mm F/2 lens 200 divided by 2 with ratio of 100. Now lets say that lens has a minimum focus distance of 10 feet. 200 divided by 2 for a 100 then divide by the minimum focus distance of 10 and we get a 10. Now if we have this same lens the 200mm F/2 and it only had a minimum focus distance of 15 the numbers would be 200 divided by 2 for 100 divided by 15 for a number of only 6.6 which would be more then double the DOF area. In these equations the higher the ending number the more control and narrower you can make your DOF. Just remember this equation and you can run a comparison against any group of lenses. Focal length by minimum F stop by minimum focus distance (200mm / F/2 / 10 = 10).

Enough talk let’s see some examples of what we are talking about.

Portraits, oh yes, how I love them and how DOF plays an important part. See the lady in red photo below and how she stands out in the photo. She’s in the center of the very small DOF area. By focusing on her with an 85mm lens set to an F stop of F/1.4 you get a shallow DOF. As you get further from this shallow DOF area items such as some of the bubbles, the little girl smiling and then even further away the background start blending away into a pleasing blurred background since they are not in the DOF area.

Product placement: Place your subject in a thin DOF area such as the ladies rings and the goblet in the photo below and you call attention to them while areas not in the DOF area are blurred away.

Super thin DOF, want to go extreme? Look at the necklace photo below. The extremely thin DOF has one single strand of jewelry in focus. Focusing is critical when taking a photo such as this. This very thin DOF was produced at 85mm and an aperture of F/1.2 and a focusing distance of only 4 feet.

What about maximum DOF? Yes that can be uesfull as well such as a landscape photo where everything must be in focus (see photo below). In this case a 32mm lens focal lenght combined with an appeture of F/9 means the DOF covers the entire photo.

Conclusion: Depth of Field or DOF is one of the best ways to emphasize your subject. Go out, experiment with different settings and see what DOF can do for you.