Specifications

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Chapter 6 Exposure and Readout 55

Readout of the CCD begins with the simultaneous shifting of all pixels one column

toward the “shift register,” in this case the column on the far right. The shift register is a

single line of pixels along one side of the CCD, not sensitive to light and used for

readout only. Typically the shift register pixels hold twice as much charge as the pixels

in the imaging area of the CCD.

Readout of the CCD begins with the

simultaneous shifting of all pixels

one column toward the “shift

the far right. The shift register is a

single line of pixels along one side

of the CCD, not sensitive to light

and used for readout only. Typically

the shift register pixels hold twice

as much charge as the pixels in the

imaging area of the CCD.

After the first column is moved into

the shift register, the charge now in

the shift register is shifted toward

the output node, located at one end

of the shift register. As each value

is “emptied” into this node it is

digitized. Only after all pixels in the

first column are digitized is the

second column moved into the shift

example is therefore D6, C6, B6,

A6, D5, C5, B5, A5, D4....

A1 B1

C1 D1

A6 B6

A2 B2 C2 D2

A6 B6

A5 B5 C5 D5

A5 B5 C5 D5 A5 B5 C5 D5

Figure 28. Full Frame at Full Resolution

After charge is shifted out of each pixel the remaining charge is zero, meaning that the

array is immediately ready for the next exposure.

Below are the equations that determine the rate at which the CCD is read out. Tables of

values for CCDs supported at the time of the printing of this manual also appear below.

The time needed to take a full frame at full resolution is:

R + texp + tc (1)

where

is the CCD readout time,

exp

is the exposure time, and

is the shutter compensation time.

The readout time is approximately given by:

= [N

· N

· (t

+ t

)] + (N

· t

) (2)