Precautions When Using The Ccd - Hamamatsu Photonics C8484-16C Instruction Manual

C8484-16C Instruction manual Ver.1.5

11. PRECAUTIONS WHEN USING THE CCD

This camera uses a CCD. Careful attention must be paid to the following points when using
a CCD:
(1) White spot
Subjecting the CCD to extended exposures may cause failure in part of the silicon
wafer, resulting in white spots. This phenomenon is not currently preventable. If the
CCD is at a fixed temperature, recurrence of the white spot increases proportionally
with the exposure time, so this can be rectified with dark subtraction. Atomic ray may
generate white spot.
*
After an image made using a certain exposure time is loaded, the CCD is exposed to darkness for the same amount of
time, and another image is obtained. After this, the difference between the images is determined, and the data for the
dark portion of the original image is nullified.
(2) Damage (drop in sensitivity) to CCD by ultraviolet light exposure
Ultraviolet light has higher energy than visible light, so it can easily damage the
sensors forming the CCD, causing a drop in sensitivity and rise dark current according
to the total incident light energy. (Example: When the CCD is exposed to ultraviolet light
having a wavelength of 196 nm and total radiation energy of 15 J/cm
with an irradiance of 0.4 mW/cm
current will increase by approximately 10 %.)
When using in the ultra violet range, take steps not to apply excessive ultraviolet light.
(If a part of the effective area of the CCD is exposed to excessive ultravio let light, such
as by direct incidence of the ultraviolet light laser, then sensitivity may drop
accordingly.)
In addition, extended exposure may cause a drop in sensitivity, even if the intensity is
not excessive. When not shot, take care to protect the CCD from ultraviolet light.
(3) Smear
When imaging very bright objects, bright vertical stripes (vertical smear) may be visible
in the images being taken. This is due to leakage of current to the vertical CCD's from
the photosensors. The amount of leakage is proportional to the readout time and
exposure time.
Smear presents no problem when the camera is in Normal frame blanking mode.
However, when using the electronic shutter of the external exposure time settings, this
sometimes becomes a problem when the exposure time is shortened.
(4) Folding distortion
A rough-edged flicker may be visible when imaging striped patterns, lines, and similar
subject matter.
(5) Interference fringes pattern
Coherent light such as LASER light may generate interference fringes pattern on
image.
(6) Over light
CAUTION
40
2
, sensitivity will drop by approximately 15 % and dark
Be careful not to input too strong light such as high-energy
•
laser into CCD chip because CCD chip may be damaged by
over light.
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for 625 minutes