Three-Dimensional Photography - Principles of Stereoscopy

118 THREE-DIMENSIONAL PHOTOGRAPHY

flash or even more, or it may be one-half or one-third. There is
no definite intensity level for daylight which may accurately be
called “normal.”
A number 3 bulb has twice that guide number at 1/25, which
means four times the intensity. A number^2 has about twice the
intensity. This simply means that a number 3 bulb at 1/25 has
the effect at 20 feet which the 25 has at lo! Not much gain is
there? The inverse square law places a most stringent limitation
upon the effectiveness of artificial light.
To make matters worse, if you wish to extend the range to 40
feet, you will need four number 3 bulbs at 1/25! So, the practical
limit must be taken as something less than 25 feet, and for the
small bulbs which we ordinarily use, that limit is about ten
feet. Of course when we make use of a blue filter or blue bulbs
we draw the limit e:ren nearer the camera.
This does not mean that the flash is ineffective. Far from it.
Once you use dayflash you will always use it, but you will soon
learn that it is primarily used for nearby objects and not for the
illumination of large areas. You will learn that it is used for light
correction rather than for primary illumination.
Once you learn the true usefulness of flash, its great advan-
tages and its limitations, you will be able to make use of it intelli-
gently. When you can do that, you will find that its value is hard
to overestimate.
Yes, it does add to the initial cost, but consider it this way. You
expose 16 pictures at a film cost of a bit less than $4. You pay the
costs of a day’s outing, perhaps $10. You encounter some subjects
which cannot be duplicated, with the value of $I.**. You find
that the effectiveness of the shots is gone, ruined by poor lighting.
$14 in cash and a day full of imponderable values gone! You add
about $2 or say 15 percent and you get 16 superb shots... does
that make flash an extravagance or an investment? Better four
good shots than 16 poor to mediocre ones. It is not a picture
which has value to you, but a good picture.