New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1899-04-09

now giving place. for a time to those VI inc
turf and aquatic sport. These latter call ior '"c
use Of somewhat more powerful aids 10 'iSio"
than the former: but inasmuch as great many
people manage to get along with opera glasses
mt races the smaller instruments VIII not re''c
into completc dcsuctude during the next six
months even though field and marine glasses
are more appropriate and satisfactory
II IS not every purchaser who knows exactly
what he wants when he comes to buy either an
opera or field glass AS consequence he
often spends more money than is necessary 10
secure the best results. or else he Is beguiied ny
ignorance and the temptation of cheapness INTO
getting n glass which is really inferior. 1t was
once frequently true of women's watches that.
while they were beautiful bits OF jewelry and
cost a good deal they were poor timckeepers
Dainty little objects for which a hundred dol
lars. or maybe several hundred dollars had
been paid have often proved much less accurate
than a 50 Elgin or a Waltham in nickel case.
So wide difference as this rarely or never eX-
lists between the qualities Of womans opera
glass and a mans, and yet good deal of money
is put into mother of-pearl and even more ex-
pcnsive adornments to an instrument which.
so far as optical excellences are concerned Is
vastly inferior to a plain black barrclied glass
FAULTS OF CHEAP GLASSES.
What constitutes a good instrument can best
be understood by noting the defects of poor
ones: such. for instance. as are incarcerated in
many OF the popular price theatres in boxes
from which they may be temporarily released
by dropping a dime into slot The lenses in
most OF these cheap glasses are so wretchedly
made that they show a ring Of color-a regular
rainbow-all around the field Of vision. Such
a glass is not "achromatic," in the first place. |
secondly, is likely to observe that cheap
glass covers only n small portion of the scene.
II the user trains it on an actor at one side of
the stage he cannot at the same moment watch
the heroine who Is on the other. Such a glass
has a small field"
! Then, very likely after trying for minute or
two to get the right focus a person will find it
impossible to obtain satisfactory results. He
may not suspect the reason. Perhaps he will
attribute the trouble 10 his lack Of skill or luck
in hitting upon the correct adjustment But
the real difficulty may be something else The
failure Of the two images produced by the two
barrels to coincide and to give a well-defned
picture is often the result of bad workmanship
in making the instrument. Unless the bigger
1ens-the object glass-s set squarey in the
barrel the pencil Of rays which it brings to a
point will not fall on the centre of the lens in
the eyepiece. but at one side of the centre The
optican would then say that the objective is
not in cOllimation with the eyepiece" But.
whatever language one employs to describe the
phenomenon. the defect itself is very serious
Still other purely mechanical faults are likely to
be found in a cheap glass
- Finally. one may notice that the degree Of en- |
largement or magnification OF the image f.
much better in one opera glass than in another
which is outwardy of the same size In speak
ing Of field glasses. it is common to say that
one maGnifes four, five or eight "diameters" |
The optician may little different phrase |
oogy. He will call one glass a "four-power. |
and another an "eight-pOwer" BY these ex- |
pressions he means that the power of the nstru |
ment is sufficient to magnify four or eight d. |
amcters.
t HOW TO TEST LENSES
The buyer can test the enlarging powers OF a |
glass himself very easily BY putting one bar |
rel to his right eye, leaving his left eye open |
and then directing his gaze to a brick wall or |
any similar checkerwork he will discover that |
the pattern is magnifed for the one eye and |
unaltered for the other. lie can thus compare |
the magnified image with the unnagnfed close |
beside it, and judge whether the enlargement |
amounts to two, three. four or five diameters.
The strong points Of good glass then are abb |
sence Of color, large field of View sharp def |
milton of the image and good magniication
for an opera glass two diameters is about all !
that one expects. But in field and marine |
glasses the magnifcation ranges from four 70
twelve diameters. A shrewd buyer will make
these considerations precedent to mere appear
nnce. Weight is another important matter; hut
1t is of less account with man than a woman