Originally posted by Marc Sabatella Hmm. I have a degree in math, but I highly distrust calculation as a way of figuring this out. DOF is more subjective than the formulas

Anyway, no reason to distrust. Just keep in mind that the Circle of Confusion (CoC) as used for DoF calculations is 20µm wheras a pixel is 5µm only, i.e., the CoC is 4 pixels wide.

If you compute the DoSP (Depth of Sharp Pixels), you therefore get 0.29cm in front and behind the subject. So indeed, the shift by 1.2cm makes you

*significantly* loose full sharpness at 100% crop pixel peeping. So, pixel peeping will indeed reveal the effect. This would even hold true (to a lesser extent) for d=3.2m distance or f/2.8.

But this is a concern only if you crop. And if you do, why did you recompose in the first place

Originally posted by Class A When I derive the formula (with simple trigonometry) I get

**x = d (1/(cos 9°) - 1)**

Class A,

I stand corrected

What great forum members we have

To my defense, what I wrote

Quote: This moves the subject away from focal plane by x = ...

was correct. But light won't take the shortest path to the focal plane, but the extrapolation of a line through lens and subject.

For normal shifts, the difference is marginal (as you pointed out).

But for a full 90° turn, my formula yields x=d (the focal plane is still there at some finite distance) where your formula correctly yields infinite (because the subject actually moved out of image for any rectilinear lens).

Originally posted by Class A Also note that if you are using a focal length higher than 50mm, the DOF will become shorter [...] the recomposition error one may be able to introduce also reduces

Yes, smaller FoV and smaller DoF counteract. If I have a spare minute, I'll check if both effects don't actually cancel out for say, a given magnification.

Originally posted by Class A Come on, what are you portraying here? A bus?

I revisited my claim that 3.2m at 50mm APS.C portraits a 50cm field. It was 2AM at night when I wrote it ... and I was wrong again

The correct distance for a 50cm FoV is 1.04m.

I've now rewritten this and my original post to correct for my mistakes. As it turns out, recompose may indeed induce a visible error in portraits shot at f/1.4.