Equipment & Techniques > Cameras, Lenses and Shooting gear

DOF and Micro Four-Thirds Format

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Dan Kehlenbach:
Hello:

I recently purchased a Panasonic G1 and have been very impressed so far with its performance.

I do have a question about depth of field with the micro four-thirds format:

Since the distance from the lens to the sensor is shorter, and since the 4/3 sensor is smaller than my APS-C Canon DSLR, will there be an inherent increase in depth of field for a given f-stop?  Would there be such things as "f-stop equivalents" between micro four-thirds and APS-C sensors?

Thanks for your help.

Dan Kehlenbach

DarkPenguin:
It's about a stop.

BJL:

--- Quote from: Dan Kehlenbach ---will there be an inherent increase in depth of field for a given f-stop?  Would there be such things as "f-stop equivalents" between micro four-thirds and APS-C sensors?
--- End quote ---
Here is my rule of thumb (but beware; many forum wars have been fought on this topic!)

Short answer:
About 2/3 stop difference between Four Thirds and EF-S or DX, 2 stops from Four Thirds to 35mm (24x36mm).
So for example, the f/2.8-3.5 lenses for Four Thirds are comparable to f/3.5-4.5 lenses for EF-S/DX for DOF wide open.


Long answer:
When photographing the same FOV with different formats, and so using focal lengths that differ in proportion to format size, you will get equal DOF if you adjust the f-stop in proportion to the change in focal length.
In other words, the same conversion factor for "equivalent focal lengths" (same FOV) also converts for "equivalent f-stops": equivalent for DOF at least(*).

Since the format conversion factors are
4/3 -> 35mm: 2x
4/3 -> EF-S: 1.25x
4/3 -> DX: 1.33x
EF-S -> 35mm: 1.6x
DX -> 35mm 1.5x
the corresponding corrections in f-stops are roughly
4/3 -> 35mm: 2 stops
4/3 -> EF-S: 0.64 stops
4/3 -> DX: 0.82 stops
EF-S -> 35mm: 1.36 stops
DX -> 35mm 1.19 stops
So about 2/3 stop between Four Thirds and either EF-S or DX.



(*) Equivalent for diffraction effects too, and maybe for "speed", once ISO speed differences are allowed for.

Dan Kehlenbach:
Thanks for the help - I am looking forward to getting out with the camera and experimenting a bit with some landscapes and close-ups.

All my best,
Dan Kehlenbach

Er1kksen:
It's also easy to remember this way: While a 14mm lens has the same apparent field of view on m4/3 as a 28mm lens would on 35mm, it's still a 14mm lens, and will have the same dof as a 14 mm lens on 35mm. A 50mm lens on m4/3 will have the field of view of a 100mm lens on 35mm, but still the dof of a 50mm lens. Field of view changes with sensor size, while dof is constant based on lens focal length and aperture, regardless of sensor size.

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