MFT Users: Do you miss the shallower depth-of-field of bigger sensor cameras?

Started 10 months ago | Discussions thread
Great Bustard
Forum ProPosts: 24,681
DOF vs background blur vs bokeh.
In reply to windsprite, 10 months ago

windsprite wrote:

Godfrey wrote:

No. I shoot with smaller format camera systems using longer lenses when I want shallower DoF.

Longer lenses can help to isolate the subect, but they don't give you shallower DOF. For the same subject magnification and aperture on the same format, a wide angle will give you the same approximate DOF as a super telephoto. It's just that the background becomes magnified with the longer lens, giving the illusion of shallower DOF. If you look at the sharp area in each photo, you will see that they are about the same.


At the opposite end of the DOF spectrum, shallow DOFs serve to isolate the subject from the background. However, while a more shallow DOF does lead to a greater background blur, it is not the only, or, in many instances, even the major player in the quantity of background blur, much in the same way that many confuse the bokeh (the quality of the out-of-focus areas of an image) with the quantity of the blur. For example, if the subject is 10 ft from the camera, 50mm f/2 will have the same framing and DOF on the same format as 100mm f/2 for a subject 20 ft away. That is, the same distance from the focal plane will be considered to be in critical focus. But the nature of the background blur will be very different -- the longer focal length will magnify the background blur.

In fact, we can be more specific. The amount of background blur (assuming the background is well outside the DOF) is proportional to the ratio of the aperture diameters. For example, while the DOF for 50mm f/2 and 100mm f/2 will be the same for the same framing (in most circumstances), the background blur will be double for 100mm f/2 since the aperture diameter is twice as large for 100mm f/2 than for 50mm f/2 (100mm / 2 = 50mm, 50mm / 2 = 25mm). A good tutorial on this can be found here.

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