Photometrics Evolve 512, User Manual

Page: 21 / 48

Evolve 512 Users Manual 9
Chapter 3
Operating Features
Introduction
The features described in this section are identical in all Evolve 512 cameras unless
otherwise stated.
On-Chip
Multiplication
Gain
As explained previously, the Evolve 512 uses a unique CCD capable of multiplying the
charge (electrons) generated in the pixels. When the multiplication is sufficiently high, it is
possible to see extremely low-light events. The amount of multiplication is controlled by the
voltage applied to multiplication register clocks. These are certified by a quantitative
multiplication gain slider which has 0-1000 steps. The calibration feature of the camera
maps the gain slider to a voltage which will provide the electron multiplication level
selected.
Offset (bias)
CCD cameras are typically designed to produce a certain level of offset (also known as bias)
when no light is present and the exposure time is set to zero (0). Typically, the user
subtracts an offset (bias) from the sample image for quantitative measurement. Since the
offset can change based on several factors such as multiplication gain, speed, etc., it is
recommended that a fresh offset (bias) image be taken with the same settings as the sample
image and then be subtracted from the sample image.
The Evolve 512 has an automatically adjusting offset switch. When a speed/gain setting is
altered, the bias valve is kept as close to a pre-selected offset as possible. This enhances the
quantitative stability of the camera.
Exposure-
Readout Modes
The Evolve 512 camera uses a frame transfer CCD and supports Non-Overlap and Overlap
exposure and readout modes. These modes are further described in the sections that follow.
Note: A frame transfer CCD has both a light-sensitive area (sensor area) and a storage area (frame
transfer area). Since the image can be quickly transferred from the sensor area to the frame transfer
area, there is no need for a mechanical shutter.