Why does the Fuji 23/1.4 have the effective DOF of a 35/2.8?

Started 5 months ago | Discussions thread
Beat Traveller
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Re: Why does the Fuji 23/1.4 have the effective DOF of a 35/2.8?
In reply to Christof21, 5 months ago

Christof21 wrote:

Beat Traveller wrote:

Randy Benter wrote:

Equivalent DoF is not the same as equivalent background blur; this is a point often lost in equivalence discussions which rarely include real photos.

Thank you. I'm glad someone finally pointed that out.

The other point to keep in mind is that depth of field distribution changes as a lens gets longer: a wide angle lens has most of the depth of field at the back, and a telephoto has about 50/50 distribution. This is a property of the lens' native focal length rather than its 35mm equivalent: which is why a compact super zoom camera doesn't show much blur until you zoom out to about 300mm equivalent (where the actual focal length is around 42mm).

So although the total depth of field might be equivalent, the distribution will be different. The shorter native lens will have more distribution towards the back, hence the background blur doesn't appear the same.

Some good explanations can be found here: http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

And here: http://photography.worth1000.com/tutorials/162260/theory-depth-of-field-vs-focal-length

At equivalent focal/aperture, like comparing APS-C 23mm f1.4 and 35m f2.1, the dof AND the background blur will be the same, At every distance, the amount of blur will be similar.

These are equivalent systems in fact.

As far as I know, there is just one exception, this is for macro.

Go back and read what I wrote.

Total depth of field is the same; depth of field distribution is different. More towards the back will be sharper for a shorter lens, independent of any equivalence.

You know why there's an exception for macro? Because depth of field is entirely dependent upon aperture and magnification. Focal length doesn't affect it. Focal length does, however, affect distribution in non-macro photography.

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