Princeton Instruments PI-MAX 3 System, Manual, Page: 88 / 150

88 PI-MAX
®
3 System Manual Version 1.A
of sharpest focus. For example, with a 50 mm lens, at f/4 the depth of field will extend
from 8 ft to infinity. By focusing at full aperture, the depth of field will be as shallow as
possible. As a result, the effects of even very small focusing adjustments will be readily
observed, allowing the focus to be set with precision. Once the optimum focus setting has
been achieved, the aperture can be reduced to the point of maximum sharpness. In some
experiments, you may wish to adjust the aperture for optimum signal level. However, the
experiment setup parameters established with the applications software can also be used
to adjust the signal level, allowing the lens aperture and focus to be optimized.
Baseline Signal
With the detector completely blocked, the CCD will collect a dark charge pattern,
dependent on the exposure time, detector temperature, and intensifier gain setting. The
longer the exposure time and the warmer the detector the larger and less uniform this
background will appear.
After temperature lock has been established, wait about 5 minutes for the detector
temperature to completely stabilize. Then try taking a few dark charge readings with the
detector operated with the I.I.T. switch set to OFF.
Note:
Do not be concerned about either the baseline level of this background or its
shape, unless it is very high, i.e., > 1000 counts (or > 3000 counts at Gain=2 for some
cameras). What you see is not noise. It is a fully subtractable readout pattern. Each CCD
has its own dark charge pattern, unique to that particular device. In addition, a small
offset is built in to prevent noise or pattern from going below zero. Every device has been
thoroughly tested to ensure its compliance with Princeton Instruments' demanding
specifications.
Temperature Lock
If the PI-MAX3 Detector loses temperature lock, the internal temperature of the camera
has gotten too high, such as might occur if the operating environment is particularly
warm or if you are attempting to operate at a too cold temperature. If this happens, an
internal thermo-protection switch will disable the cooler circuits to protect them.
Although the thermo-protection switch will protect the camera, users are advised to
power down and correct the operating conditions that caused the thermal-overload to
occur. Note that the cooling performance of the detector can be enhanced by circulating
water coolant.
See "Temperature Control" , page 36.
Turn the controller off for fifteen or twenty minutes. Then turn it back on and set a
warmer temperature from the software
Detector Temperature dialog box. Temperature
lock should be re-established within a few minutes.
Intensifier Alarm
Contact the factory at once if sporadic or continuous unwarranted alarms occur. They
may indicate intensifier damage or another situation that requires immediate attention.
To reduce the risk of detector damage, PI-MAX3 detectors are equipped with an audible
alarm in the detector head, activated when the intensity of light falling on the image
intensifier exceeds a preset threshold. While the alarm is sounding, the photocathode is
temporarily disabled. Toggle the
I.I.T. switch on the back of the PI-MAX3 to the OFF
position. Cover the detector window and only switch the I.I.T. switch to ON after the
Caution