PASCO OS-8500 INTRODUCTORY OPTICS SYSTEM - Manual (Page 72)

Introductory Optics System 012-02744K
®
66
Exp 20: The Magnifier
Suggestions on – Procedure
➀
No. According to the fundamental lens equation
the magnification, and the angular magnification,
are unlimited. The limit of useful magnification is
caused by spherical aberration in the lens.
➁
The 75mm lens provides greater magnification.
➤ Note: As a demonstration that the limit to
useful magnification is caused by spherical
aberration, put the variable aperture in position
just in front of the 75mm lens. Close the aperture
as far as practical without losing the image
completely, and then move the lens/aperture set
as far from the object as possible without losing
focus (about 9-11 cm). While looking through
the lens, widen the aperture. The image will
become almost completely blurred.
Another Note: The actual angular magnification
depends on the distance from the eye to the lens,
as well as from the lens to the object.
θ
'= ±
fh
o
d
e
d
o
± f d
o
+ d
e
where d
e
is the
distance to the eye.
if d
e
= 0, then the angular size is the same as if
there were no lens there at all. This is why
contact lenses do not change the apparent size of
things, although they do affect the focus.
➂
Angular magnification = 25 cm/f.
75 mm = 7.5 cm: power = 3.33
150 mm = 15 cm: power = 1.67
➃
Power = 25/50 = 1/2. This would have limited use
as a magnifier; it just wouldn’t be strong enough to
make much difference.
Exp 21: The Telescope
Suggestions on – Procedure
➀
The angular magnification of the telescope is 2.
(150/75) If the telescope is looked through back-
wards, the lenses are reversed in the equation and
the magnification becomes 1/2.
➁
About 2.1. One of the best ways of measuring this
is to look at a meter stick with both eyes open (one
eye through the telescope). Then you will see both
the unmagnified and magnified images at the same
time, and you may compare their sizes using the
scales on the images. The magnification observed
will generally be slightly larger than the theoretical
value, since the object you are looking at is not an
infinite distance away.
➂
About 1/2, using the same method as in part 2.
➃
Yes.