[Leica] Re: Depth of field... (more than you wanted to know)

[pieter@world.std.com (Pieter Bras)]

Jim Brick <jimbrick@photoaccess.com> wrote:
> 
> ... Depth Of Field (DOF) is a function of f/stop, image size, and
> acceptable Circle Of Confusion (COC).  An 80mm lens on a YashicaMat
> has precisely the same DOF as an 80mm lens on a Hasselblad, in every
> situation.  One does not give less or more DOF than the other.  Set
> them side by side, use the same f/stop, and the DOF will be identical.

Thanks, you've just cleared away a lot of fog on this subject.

> What f/stop you use and where you focus in your scene will determine how
> much is in focus.  From the exact point of focus, DOF extends 1/3
> forward (toward the camera) and 2/3 back (away from the camera).  If you
> photograph a tight face composition, at wide open (f/2.8 or f/3.5) and
> focus on their eyes, there is a good chance that the end of their nose
> will be out of focus.  If, however, you focus on the tip of their nose,
> their eyes will be in focus.  Except for perhaps Pinnoccio.

I think out-of-focus foregrounds are more disturbing than out-of-focus
backgrounds, and don't care for portraits with eyes (or one eye!) in
focus, and a fuzzy nose.  Unless there was a deliberate striving for
effect, it looks to me the like photographer just botched the shot.

> A mediocre lens will "appear" to have more DOF than an first class lens.
> This is because those things that are in focus (at the plane of actual
> focus) will appear to be extra sharp and then fall off to not so
> critically sharp (acceptable COC) within the wanted DOF range.  While a
> mediocre lens will not have that extra critical sharp area, it will
> blend better with the acceptable DOF range.  There is no abrupt
> transition.  So the better your lenses, the more visible the transition
> between the very narrow critical sharp plane of actual focus, and the
> rest of the photograph.

So, is it always a good thing to have one "very narrow critical sharp
plane" stand out from the rest of the image?  That's not how my eyes
register the world.  But I suppose it's great for those two-dimensional
wall charts that lens testers love to use.

"Mediocre" is as mediocre does.  In other words: results matter more
than specs or test measurements.  "Better" may not always be better.

> In order for your photographs to turn out as your mind's eye sees them
> when you are taking them, you must understand DOF, how it works, its
> limitations, and how to get around the limitations.

Or use a pinhole. :)

- -- 
Pieter Bras