P3D Re: Rever DOF scale: stereo fantasy

[Paul Talbot <ptww@xxxxxxxxx>]

Michael Kersenbrock wrote:
> The chart on the underside of the lid on my older Realist says
> that at f/16 the DOF is 4' to Infinity.
> 
> I think on the camera focusing scales, the distance between
> 40' and infinity is pretty small while the difference betwee
> 3' and 4' is pretty big,

It *is* very big.  One of my main points was that small differences
in distance at close ranges make a huge difference in focus.

> so exactly where one sets things
> (plus the circle of confusion def'n) can make quite a difference.

Agree.

> >
> > Be very wary of those DOF scales on the Revere!
> 
> And the Realist Cover?  Not much different than the Revere!

I beg to differ.  The distance between 3 feet and 4 feet is huge
when you are talking about focus.  On the DOF scale on the Realist,
setting 3 feet as the f/16 near point gives a far point of 8 feet,
but setting 4 feet as the f/16 near point gives a far point of over
25 feet.  On the Realist focus dial, I estimate it is about 75 to 80
degrees of arc from the 3 foot marker to the 4 foot marker.  On
the DOF scale, setting infinity at f/16 gives a near point of about
4-3/4 feet, a full 90 degrees of arc (1/4 turn of focus wheel!) from
the 3 foot mark.

I learned of the problems with the Revere DOF scale through
ruined pictures, BTW.  This is not just academic discussion.

I'd also like to advise any new stereophotographers who may be
reading this that the distance ranges specified between the f/16
marks on the DOF scale (and discussed above) are generally too
large for comfortable viewing of the results.  Try to limit the
depth range of your scene to a distance contained within the f/8
marks of the DOF scale--of a Realist!  ;)

Paul Talbot


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