DOF vs Bokeh
I write this article because some people still confuse the difference between depth of field (DOF) and bokeh. Honestly I don’t want to write this article but in the end I decide to write this article. Not very comprehensive article but I think you should check this out.
First, we can check the definition from wikipedia.
Depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.
Bokeh is the blur or the aesthetic quality of the blur, in out-of-focus areas of an image, or “the way the lens renders out-of-focus points of light. Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting—”good” and “bad” bokeh. Bokeh occurs for parts of the scene that lie outside the depth of field.
Look back to my article in 2009 about “How to Use Maximum Aperture Effectively“, DOF is determined by aperture, focal length, and subject distance. You can read that article because it’s very important.
I never make a tutorial about “bokeh” but in my opinion bokeh is determined most by the lens.
Take some information from wikipedia:
Bokeh characteristics may be quantified by examining the image’s circle of confusion. In out-of-focus areas, each point of light becomes an image of the aperture, generally a more or less round disc. Depending how a lens is corrected for spherical aberration, the disc may be uniformly illuminated, brighter near the edge, or brighter near the center. Lenses that are poorly corrected for spherical aberration will show one kind of disc for out-of-focus points in front of the plane of focus, and a different kind for points behind. The shape of the aperture has an influence on the subjective quality of bokeh as well. For conventional lens designs (with bladed apertures), when a lens is stopped down smaller than its maximum aperture size (minimum f-number), out-of-focus points are blurred into the polygonal shape formed by the aperture blades. This is most apparent when a lens produces hard-edged bokeh. For this reason, some lenses have many aperture blades and/or blades with curved edges to make the aperture more closely approximate a circle rather than a polygon.
I hope that you clear for the definition and explanation hehe….
Now imagine that you have 3 expensive lenses: EF 50mm f/1.0L, EF 85mm f/1.2L II, EF 200mm f/2L IS.
Assume you use the same camera body and shooting the same object in the same frame / magnification (the fair way to compare should be the same frame, not the same subject distance). Lenses to be set in their maximum aperture (f/1.0 for 50mm, f/1.2 for 85mm and f/2 for 200mm), which one that create narrowest DOF? and which one that create better bokeh photo?
I never try in the reality, but in my opinion EF 50mm f/1.0L will create the narrowest DOF. You can use DOF calculator to measure the DOF. I have noted in previous that object should be taken in the same frame / magnification, means that the difference in focal length will be balanced in the subject distance (approximately). So the biggest aperture will create the narrowest DOF.
For the other question, it is more difficult to be answered. I ever read the article from Bob Atkins, he mention about physical aperture. The physical aperture is focal length divide by f number, for example: 85mm f/1.2 (physical aperture = 70.83mm). In other article he mention that “If the background is far enough away (well outside the depth of field) and the subject if fairly close (well inside the hyperfocal distance) the degree of blurring is related to the absolute physical size of the lens aperture”. You better to check the link and you will understand it.
So regarding the second question, it’s depend on the distance (if the subject distance is close, and the background is too far) then the answer should be EF 200mm f/2L IS (based on physical aperture). I don’t own EF 50mm f/1.0L so I can’t compare the bokeh quality ~ but comparing EF 85mm f/1.2L II with EF 200mm f/2L IS – I think EF 200mm f/2L IS produce more smooth bokeh.
In photography, both DOF and bokeh are important, although for most cases (not all cases) the first priority should be DOF then bokeh (in my opinion).
I will give you an example case which DOF is more important than bokeh. The photo below is taken with EOS 5D II + EF85mm f/1.2L II. The first priority is to maintain the subject in focus (so I set the aperture at f/2.8 instead of f/1.2) – and the second priority is bokeh (so I set the aperture at f/2.8 instead of f/16). I think you understand what I mean hehe…
In addition, I will give you an example which bokeh is more important than DOF. Below you can see there is no object that in-focus area. In this case, as a photographer – my priority is getting “the bokeh” instead of maintaining some areas in focus.
Well, I think this article is a little bit technical and maybe boring for you ^^. I hope you get some useful knowledge from this article. Thanks for reading my article.