PASCO OS-8524 User Manual

Instruction Sheet

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f/5.6

f/4

f/22

f/16

f/11

f/8

OS-8524

APERTURE
ACCESSORY

BASIC
OPTICS

17.7 mm DIA

25.0 mm DIA

4.4 mm DIA

6.3 mm DIA

8.8 mm DIA

12.5 mm DIA

f STOP FOR

100mm F.L. LENS

f

for the PASCO
Model OS-8524

APERTURE ACCESSORIES

012-05882A

1/96

$1.00

Spherical Aberration

Attachments

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Central (center) Mask

Peripheral (outer) Mask

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Introduction

The Pasco OS-8524 Aperture Accessories are designed to
be used with the PASCO OS-8515 Basic Optics System.

The Aperture Disk provides 6 holes, corresponding to ƒ/
4, 5.6, 8, 11, 16, and 22 apertures for a 100 mm lens (in­cluded with the PASCO OS-8515 Basic Optics System).

The Spherical Aberration Attachments enables the user to
investigate how the center and outside parts of a lens fo­cus light in different planes.

Equipment

This set includes two different accessories to the Basic
Optics System (OS-8515):

– An Aperture Disk for demonstrating the ƒ-stops

used in cameras.

– Spherical Aberration Attachments for masking the

center and outer areas of a lens to show spherical
aberration.

Aperture Disk

f/16

6.3 mm DIA

f/22

4.4 mm DIA

f/4

25.0 mm DIA

f/5.6

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100 mm

lens

17.7 mm DIA

ACCESSORY

APERTURE

OS-8524

100mm F.L. LENS

8.8 mm DIA

f STOP FOR

f/11

OPTICS

BASIC

12.5 mm DIA

f/8

Aperture Disk

Central or

Peripheral Mask

optics bench

Figure 1: Aperture Accessories Assembly

Aperture Disk

When the aperture size is reduced by one setting, the in­tensity of the light transmitted through the smaller aper­ture is half the intensity through the next larger aperture.
The 6 apertures on this disk correspond to 6 ƒ-stops as
defined in photography. The ƒ-stop is defined as follows:

Assembly

Simply snap the Aperture Disk, Central Mask, or Periph-

value =

focal length of the lens

diameter of the aperture

eral Mask onto a lens from the Basic Optics System. See
Figure 1.

®

10101 Foothills Blvd. • P.O. Box 619011 • Roseville, CA 95678-9011 USA

Phone [phone] • FAX [phone] • email: [e-mail]

© 1996 PASCO scientific
This instruction sheet written/edited by: Ann Hanks

better

ways to

teach science

Aperture Accessories 012-05882A

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Table 1: Aperture Disk Specifications

ƒ-stop ƒ-stop calculation

ƒ-4

ƒ-5.6

ƒ-8
ƒ-11
ƒ-16
ƒ-22

24= 4.00
2

= 5.66

2

= 8.00

7

2

= 11.31

2

= 16.00

2

= 22.63

aperture diameter

100 mm

=XXX

ƒ-stop

25.0 mm

17.7 mm

12.5 mm

8.8 mm

6.3 mm

4.4 mm

The ƒ values are chosen to be powers of the square root
of 2. This disk is designed to be used with a lens of focal
length 100 mm (10 cm). See Table 1 for the correspond­ing ƒ-stops and diameters.

Using the Aperture Disk

To mount the aperture disk to the optics bench (OS-

8515), press the mounting ring into the lens holder that
contains the 100 mm focal length lens (see Figure 1). To
select different apertures, the disk is rotated until it clicks
into place with the desired aperture positioned at the cen­ter of the lens.

Suggested Experiments for the Aperture Disk:

➁ Repeat this procedure using a smaller aperture to show

that “stopping down” gives a greater depth of field
(i.e., the image will stay in focus over a larger range of
screen positions).

Spherical Aberration Attachments

The spherical aberration attachments press into any lens
holder in the Basic Optics System (OS-8515).

Suggested Experiments:

Show spherical aberration of a lens

➀ Use the 100 mm lens to focus the image of the lighted

object on the screen.

➁ Put the outer-mask spherical aberration attachment on

the lens and refocus the image by moving the screen.
Note which way the screen must be moved to bring
the image into focus.

➂ Put the center-mask spherical aberration attachment

on the lens and refocus the image by moving the
screen. Note which way the screen must be moved to
bring the image into focus. Are the rays that pass
through the outer edge of the lens bent more or less
than those that pass through the center portion of the
lens?

Show that the intensity of an image is halved with each
incremental decrease in aperture size

➀ Using the 100 mm lens with the aperture disk set on

its largest aperture (ƒ-4), focus the image of the
lighted object on the screen.

➁ Use a digital photometer (such as SE-9087) at the po-

sition of the screen to determine the intensity of the
image. Or use a comparative photometer (such as OS-

8520) at the position of the screen (with the screen re­moved) and find the intensity relative to a second light
source.

➂ Select the next smaller aperture (ƒ-5.6) and measure

the new light intensity to show that the light intensity
is half of the previous value. Repeat this for all the ap­ertures.

Show how the aperture size affects the depth of field

➀ Put the screen 50 cm from the light source. Use the

100 mm lens with the ƒ-4 aperture to focus the object
on the screen. Check how far the screen can be moved
without noticeably changing the sharpness of the im­age.

Show color aberration

➀ Use the 100 mm lens with the center-mask to focus

the image of the lighted object on the screen.

➁ Move the screen away from the lens until the image is

blurred. What color does the image appear to be?

➂ Move the screen toward the lens passing through the

focused point until the image is blurred again. Now
what color does the image appear to be? Which color
(red or blue) is bent more as it passes through the
outer part of the lens?

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