[photo-3d] Re: DOF & Rangefinder

["Chuck Holzner" <cfholzner@xxxxxxxx>]

--- In photo-3d@xxxxxxxxxxx, "Dr. George A. Themelis" <drt-3d@xxxx> 

> Chuck, look at your Realist and tell me how you are going
> to focus it at 30 feet.  

Interpolation.  Nothing is ever exact.

The last marked division before
> infinity is 25 feet.  Might as well focus at 15 feet, 25 feet
> or infinity.  

But definitely not 8 feet.

At f16 you are not going to see any difference,
> I guarantee it.

I have in the past, tree lines at a distance.


> Basically, you prove my point that you don't need to know
> the location of the nearest or furthest point with any
> accuracy.

I don't see how I did that.  Basically or not you should have "some" 
accuracy.

> 
> I am not advocating blind use of the hyperfocal distance.
> I am also not saying that the rangefinder is useless.

Thank you.  Exactly my point.

> But I do say that you are wasting your time if before
> every stereo picture you use your Realist's rangefinder
> to figure the exact distance of the near and distant
> objects, do some mental calculation to determine the 
> optimum focusing distance, and then set the aperture 
> at f16.
> 

Most of the time I have infinity (or long distances) in the shot so 
all I have to do after measuring the near range is to double it and 
set it.  You don't need a Dr. Degree in math to double a number 
quickly.  As far as mental calculations go, that is what the DOF 
scale is for; it is not difficult to learn.  I don't always use F16 
and it doesn't hurt to have the DOF set optimum.

Chuck