PASCO OS-8539 Educational Spectrophotometer - Manual (Page 13)

®
M o d e l N o . O S - 8 5 3 7 a n d O S - 8 5 3 9 S e t U p
9
To mount the clamp on a support rod, loosen the other thumb-
screw. Put the support rod though the hole, and then tighten the
thumbscrew (Fig 15).
Mounting and Adjusting the Collimating Slits and Lens
The Collimating Slits consist of two parts: the Collimating Slits
Plate and the Collimating Slits Holder. The slits are in a piece of
metal that is attached to a moveable slide. The slide is held on the
Collimating Slits Plate with a small thumbscrew and two perma-
nently attached socket screws. The Collimating Slits Plate is
attached to the Collimating Slits Holder with two brass thumbscrews. Loosen the small thumbscrew in the Colli-
mating Slits Plate in order to move the slits slide back and forth. The narrow slot in the Collimating Slits Plate
lets light through one slit at a time. The top half of the Collimating Slits Plate helps to prevent extra light from
being measured.
Snap the Collimating Slits Holder into the Optics Bench near the end of the
bench that is closest to the light source you are using. To move the holder,
grasp the holder at the base and push in on the locking clip on one side of
the holder (Fig. 16). Slide the holder along the center section of the bench
while squeezing the clip. Release the clip to lock the holder firmly in posi-
tion.
Snap the Collimating Lens Holder into the Optics Bench between the Colli-
mating Slits Holder and the Spectrophotometer Base. Position the Colli-
mating Lens Holder about 10 cm from the Collimating Slits Holder.
Positioning the Collimating Slits and Lens
The focal length of the Collimating Lens is about 10 cm so the lens should
be positioned about 10 cm from the slits. Use the following procedure to
position the lens more precisely.
Set up a light source so that light from the source passes through one of the slits on the Collimating Slits and then
through the Collimating Lens. Rotate the Light Sensor Arm so the Aperture Bracket and Light Sensor are out of
the way and the beam of light can shine onto a distant vertical surface such as a wall (Fig. 17).
Adjust the distance between the Collimating Slits and
the Collimating Lens so that the beam of light is neither
converging nor diverging (i.e., light rays are parallel).
The beam of light should stay about the same width all
the way to the distant vertical surface. Hold a piece of
paper in the light beam’s path at various distances
along the beam’s path. Check to see that the light
beam’s width is about the same at each point along its
path. Note that the light may not be in focus during this
process.
If the light beam is not perfectly vertical, loosen the small thumbscrew that holds the Collimating Slits slide and
adjust the slide, or loosen the brass thumbscrews that hold the Collimating Slits Plate onto the holder and adjust
the plate until the collimated beam is vertical. Remember to tighten the thumbscrews after you make the adjust-
ment.
The distances between the light source and the Collimating Slits and between the Collimating Slits and the rest of
the Spectrophotometer are not critical. However, the closer the light source, the brighter the spectrum.
Figure 15: Mounting Clamp onto Rod
Optics Bench
Rod
Figure 16: Locking Clip
Collimating Slits
Optics Bench
Locking clip
GAIN 10 100
1
Figure 17: Collimation Setup
Light
source
Collimating
Slits
Collimating Lens
Light ray
path