PASCO SP-9268A STUDENT SPECTROMETER - Manual (Page 13)

9
012-02135F Student Spectrometer
¨
The optional Gaussian eyepiece (Model SP-9285) sim-
plifies the task of aligning and focusing the spectrometer
and aligning the diffraction grating. One Gaussian eye-
piece can be used to align and focus any number of spec-
trometers, so only one is generally needed per lab.
To Align and Focus the Spectrometer Using
the Gaussian Eyepiece:
1. Remove the telescope eyepiece and replace it with
the Gaussian eyepiece.
2. While looking through the telescope, slide the eye-
piece in and out until the cross-hairs come into sharp
focus. Loosen the graticule lock ring, and rotate the
graticule until one of the cross-hairs is vertical. Re-
tighten the lock ring and then refocus if necessary.
3. Plug in the power supply of the Gaussian eyepiece.
The light from the eyepiece is reflected along the op-
tical axis of the telescope by a half-silvered mirror.
Looking through the eyepiece, you'll see the cross-
hairs lighted up as they scatter some of the light back
into the eyepiece.
4. Mount the grating holder to the spectrometer table
and insert the diffraction grating.
5. Looking through the telescope, rotate the table until a
patch of light is reflected back through the telescope
from the glass surfaces of the grating. The spec-
trometer table and the telescope must be at least
roughly level to achieve this reflection. If they are
not, see Realigning the Spectrometer, earlier in the
manual.
6. Adjust the focus of the telescope until the cross-hairs
and their reflected images are in sharp focus. The
glass slides of the grating are not efficient reflectors,
so you must look carefully to see them.
IMPORTANT: The grating is sandwiched be-
tween two glass slides so, depending on how par-
allel the slides are, you may see as many as four
reflected images of the cross-hairs. In the follow-
ing steps, you will be instructed to superimpose
the graticule with its reflected image. If there is
more than one image, just center the cross-hairs as
accurately as possible between the images.
7. Use the table rotation fine adjust knob to align the
vertical cross-hair with its reflected image.
8. Adjust the spectrometer table leveling screws until
the cross-hairs are superimposed on the reflected im-
age.
9. Rotate the spectrometer table 180 ° and, using the
table rotation fine adjust knob, align the vertical
cross-hair with the reflected image.
10. Adjust the table leveling screws to remove half the
separation between the horizontal cross-hair and the
reflected image. Adjust the telescope leveling
screws to remove the remaining error, so the cross-
hairs and their reflected images are superimposed.
1 1. Repeat steps 9 and 10 until the cross-hairs and their
reflected images are superimposed from both sides
of the diffraction grating.
12. Unplug the Gaussian eyepiece. Adjust the slit of the
collimator so it is open and vertical.
Appendix: Using the Gaussian Eyepiece