
from Dr. Bruette, editor of FOREST 
AND STREAM, from which the fol- 
lowing is an extract: 
Sr time ago I received a letter 
“Ever since I can remember, the 
market has been flooded with inferior 
articles. One of my first invest- 
ments as a boy was a hard-earned 
dollar that I sent away to a mail- 
order house for a telescope that was 
guaranteed to enable one to see three 
miles. I do not know of anything 
more useful than a good pair of 
binoculars, nor anything that is more 
useless than a bad pair.” 
If Dr. Bruette had devoted many years 
to the study of this subject, he could 
not possibly have made a more apt 
statement. It is deplorably true that 
while we all have decided opinions about 
shoes or watches, guns or motor 
cars, most of us are rather in the dark 
when it comes to the selection of a field- 
glass. 
The responsibility for this condition 
may be charged to the manufacturer 
of field-glasses who for 
some unaccountable reason 
has surrounded his prod- 
uct with a cloak of mys- 
tery, very much as does 
the druggist in compound- 
ing prescriptions. With i 
here and there a notable 
exception, these manu- D 
facturers have _ limited 
their descriptions to pure- C 
ly technical terms. 
T shall be my endeavor 
to present the subject in 
such form that you who 
read will become familiar 
with field-glasses in gen- 
eral, and when the time 
comes for you to add a 
binocular to your belong- 
144 
ings, you will do so with that confidence 
only acquired by knowledge or experi- 
ence. 
It is needless for me to dwell on 
the history of field-glasses. Many 
technical books have been published on 
the subject, which those who are in- 
terested may readily consult. Suffice 
it to say that from the day, some cen- 
turies ago, when it was discovered that 
a curved piece of glass would produce 
an image, the efforts of scientists have 
been devoted to obtaining and improy- 
ing upon various aids to vision. 
ROM these early efforts we obtained 
the first telescope which merely con- 
sisted of an object lens or “objective” 
which formed an image of a distant 
object, and an eyepiece or “ocular” with 
which to view the image obtained. Two 
such telescopes combined produce a 
binocular. Right here let me answer 
the oft-repeated question, ‘“What is the 
difference between a field-glass and 
binocular?” There is no difference, for 
any optical instrument, be it field- 

Path of rays in a Zeiss Silvarem 
The Story of 
The Prism Binocular 
The Sportsman’s Field Glass 
_. Comprehensively Explained 
By WILLIAM HARTMAN 
glass, telescope or microscope, adapted 
to vision for both eyes at once, is a 
binocular. 
UITE naturally two such tele- 
scopes combined to make a binocu- 
lar field-glass resulted in glasses which 
were somewhat limited in their useful- 
ness, due to the extremely narrow 
angle of view produced. This restric- 
tion was overcome by the application 
of the principle of reversing prisms re- 
sulting in the prism binocular, by means 
of which the objectives or object lenses 
could be set further apart than the 
distance of the eyes, thereby broaden- 
ing the scope of vision or field of view. 
For while good magnification in a field- 
glass is of paramount importance, the 
lateral distance or “field’ which may 
be covered at one glance is of equal 
value in determining the efficiency of 
the glass. The illustration showing 
the “path of rays” will readily enable 
the reader to follow the course of light 
in a prism binocular. Here we see the 
light image entering the Objective A 
to Prism B where it is re- 
flected to Prism C and 
again reflected and pro- 
jected through Collecting 
Lens D to Ocular E. Note 
that the distance between 
the two objectives is al- 
most twice that of the dis- 
tance between the oculars 
or eyepieces. The effect 
obtained is comparable to 
that which would result 
from an increase of the 
distance between the eyes. 
ne great superiority 
of the prism binocu- 
lar over the ordinary or 
Galilean type of field- 
glass was evident, but still 
greater improvements 
ia 
