Originally posted by kevinschoenmakers You could've just mentioned you were talking about keeping the same distance to the subject...
To compare stuff, some standard is needed. Otherwise we're in apples-n-oranges land. I can easily prove that (say) 30/2 and 30/6 have the same DOF, or that 30/2 and 30/2 have very different DOF -- all I have to do is radically change distances. Sort of like 1+1=3, for large enough values of 1.
[/me dons Cloak Of Authority...] So, shorter focal lengths have thicker DOF than do longer focal lengths, unless we move stuff around till the numbers fit. Or think of it as, ALL ELSE BEING KEPT THE SAME, here's how factors affect DOF:
* Thicker DOF: Shorter focal length AND/OR tighter aperture AND/OR further subject-lens distance
* Thinner DOF: Longer focal length AND/OR wider aperture AND/OR closer subject-lens distance
The ALL ELSE includes angles, lighting, display size and type, viewing distance, viewer vision and consciousness, etc. Do I have enough epoxy to glue-down all of those? [/me hate epoxy and epoxy hates /me]
Once we skip around the ALL ELSE BEING KEPT THE SAME part, anything can happen. That Primogon's 35/4.5 DOF becomes razor-thin. My 135/2.5's DOF becomes thick as a brick. French poodles start talking. Economic crises are fixed. My old 1996 Ford Exploder gets 255 mpg. Miracles!! Yah, numbers are fun!