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Centering the Crystal
1. Retract the manual ATR crystal using the toggle bar, by lifting the bar then twisting
counterclockwise.
OR
Click the
button to retract the automated ATR crystal.
2. Place a piece of black PVC electrical tape on a microscope slide, and put the slide on the
microscope stage.
3. Move the stage so that the tape is directly below the crystal, and focus the beam on the
tape.
4. Lower the crystal onto the tape.
If the crystal height is adjusted correctly, it will just touch the tape and make a shallow
impression in it.
5. Retract the crystal.
If there is no impression on the tape, the crystal height should be lowered slightly by
turning the knurled height-adjustment nut left to right a quarter of a turn.
If there is a deep impression on the tape, which does not disappear within a few
seconds, the crystal height should be raised slightly by turning the knurled height-
adjustment nut right to left a quarter of a turn.
6. If appropriate, repeat steps 4 and 5 until the crystal just touches the tape.
7. Once the crystal height has been corrected, look at the impression of the crystal on the
tape. Decide whether the impression is in the center of the field of view.
If the impression is in the center of the field of view, the assembly is aligned.
If the impression is not in the center of the field of view:
1. Loosen the two knurled thumb-nuts under the ATR crystal holder half a turn
(Figure 34).
NOTE: The centering adjustments are the same for both the manual and automated ATR
objectives.
Figure 34 Centering the ATR Crystal
Techniques for Collecting Spectra . 85
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