[photo-3d] Re: hypers airplane and lightning

["Abram Klooswyk" <abram.klooswyk@xxxxxx>]

John Toeppen Jan 10, 2001:
>BTW, 40 ft separation shows depth in clouds out to about 3 
>miles away, 150 ft does 10 miles well. No trees in the 
>foreground please....

Is this true, can we check it, and how about other distances?

Some calculations, which are easier in metric units. 
1 foot =  30.48 cm = 0.3048 meter,  and  1 mile = 1609 meter.
"Normal" stereophotographs are taken with 2.5'' or 65 mm base.

40 feet separation is  40 * 0.3 m = 12 m, that is about 190 x 
normal base. Depth is seen "to about 3 miles",  or 3 * 1600 m 
=  4800 m. Divided by the 190 x factor we get 25 meter, which is 
indeed a distance at which we see depth with a "normal" base. 
And 4800 / 12 = 400.

A similar calculation for the other case: 150 feet is 150 * 0.3 m 
= 45 m, about 700 x the normal base. Depth to 10 miles is to 16000 
meter (=16 km). Divided by 700 gives 23 meter, so about the same as 
stated for the 40 feet base. And 16000 / 45 = 360.

Suppose 25 meter or 80 ft is a good choice for the distance to 
which you "normally" can see good depth. As 2500 cm / 6.5 cm = 
385, the rule would be: 
Take a base 1/350 to 1/400 times the distance to which you 
want to see depth.

(And about the foreground trees: Multiply the calculated base 
by 30, have nothing closer.)

Abram Klooswyk