[MF3D.FORUM:327] Re: 1/30 Yes!

["Harold Baize" <baize@xxxxxxxxxxxxx>]

Oleg,

I'm sure you use the right lens separation because
I have enjoyed your variable lens separation images
at the Oakland Camera Club on many occasions. Your
images have ample depth and rarely cause eye strain.

In defense of the 1:30 "rule" you present your
results using a 70mm lens and the give the
deviation from John B's General Solution formula.
Your results ranged from 0.5% to 13% different.
However, when I applied the formula to your second
example I found a lens separation of only 0.603 inch.

>From your second example (low landscape with clouds)
using the General Solution formula:

base offset = d*(far*near/far-near)*(1/focal - 1/focus)

d is set at 0.0012m
far is  10,000 ft (3048m)
near is 3 ft (0.914m)
lets try a focus at 3 meters
focal length is 70mm (0.07m)

Solving for this equation gives 0.01531 meters, or
0.6026 inches. This is far less than your result of
1.18 inches. Of course you might have used a different
focus point, but solving for a focus at 30.48 feet
(10 meters) still gives 0.01556m (0.613 inches).

To find this I first went to the internet and found
a conversion utility to make the conversions from
metric to English measures. The utility is called
Conversion Buddy.
   http://users.ntr.net/~jpresley/

Then after double checking my figures I was fairly
confident. Still I may have not correctly applied
the formula and maybe my math is off. However
I followed the text carefully. In fact the
numbers seem to be half of what they should be,
even though the equation is suppose to give the
stereo base (bO), not half (bO/2).

What is my point.. I really want to make the
point, that the 1:30 "rule" is not a
rule, it is a heuristic. A simple and quick
way to find a solution that works in most situations
well enough to make more precise calculation
unnecessary. If one needs to use a calculator and
a metric conversion utility to find basically the
same result (or make a mistake and be way off),
then the argument is strong for using the simple
heuristic.

Harolddd

>
> Details:
>
> Typical landscape with clouds:
>  Near point: 6 feet
>  Far point: 100,000 feet (19 miles)
>  True stereo base: 2.41 inches
>  1/30 rule’s base: 2.40 inches
>
> Low landscape without clouds:
>  Near point: 3 feet
>  Far point: 10,000 feet (2 miles)
>  True stereo base: 1.18 inches
>  1/30 rule’s base: 1.20 inches
>