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QSI 500 SERIES USER GUIDE

CCD Imaging Overview

This section is intended only as a brief overview of CCDs and CCD Imaging. If you are new

to CCD imaging there are a number of excellent books that you can use to gain a deeper

understanding of the issues and techniques. Two very well regarded books that we

recommend are:

 The New CCD Astronomy

by Ron Wodaski

 The Handbook of Astronomical Image Processing

by Richard Berry and Jim Burnell

How CCDs work

Charge Coupled Devices (CCD) work by converting photons into electrons which are then

stored in individual pixels. A CCD is organized in a two-dimensional array of pixels. The

CCDs used in the QSI 500 Series cameras at the time of printing range from roughly

400,000 pixels (768W x 512H) to 8.3 million pixels (3326W x 2504H).

Each pixel can hold some maximum number of electrons. CCDs currently used in the QSI

500 Series can hold from 25,500 to as many as 100,000 electrons depending on the

specific model of CCD. While integrating (exposing) an image, photons strike individual

pixels and are converted to electrons and stored in each pixel well. The effectiveness of

this process is referred to as Quantum Efficiency (QE). The number of electrons stored in

each pixel “well” is proportional to the number of photons that struck that pixel. This linear

response is one of the key traits that make CCDs exceptionally well suited to astronomical

imaging. A subject that is twice as bright will build up twice as many electrons in the CCD.

After an exposure is complete, the electrons in each pixel are shifted out of the CCD and

converted to a number, indicating how dark or light each particular pixel was. Those

brightness values for each pixel are then stored in the image file, typically a FITS file for

astronomical imaging.

Types of CCDs

CCDs are available in a variety of designs and technologies. QSI 500 Series cameras

currently employ two different types of CCDs, Full Frame and Interline Transfer, with

numerous optional features.

Full-Frame CCDs

Full-Frame CCDs generally provide the highest sensitivity and the widest linear response

range of these two types of CCDs. These characteristics make full-frame CCDs ideally

suited to astronomical imaging. Full-frame CCDs must employ a mechanical shutter to

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QSI 520c Guía de usuario Pagina 31