Digital Astrophotography
DRAFT
Most astrophotography is now done using digital imaging equipment and techniques. While there are still some people who do astrophotography on film, most astrophotographers prefer the advantages digital imaging offers.
It helps to understand the basics of digital imaging, how cameras work, how color is captured, and the advantages that digital imaging offers over film.
Advantages
One of the key advantages is the fact that digital imaging does not require film, and, therefore, photographers can capture an unlimited number of images and not need to use chemicals to process them. Processing film requires specific equipment, chemicals, and techniques that the average person does not possess. Most people have a computer or access to one, and digital cameras have far surpassed the availability of film cameras.
With film, if you don't have the development equipment and chemicals, you could send the film out for processing, but few processing companies would have the expertise needed to process the images properly to get good prints. Most astrophotographers had to do the work themselves.
With digital imaging, image files are saved as a set of numeric values, and this affords us the opportunity to use mathematics to transform and enhance the data. This above all else changes the game for amateur astrophotography.
Image Sensors
And image sensor in a digital camera is an electronic component that senses light and quantifies it. Fundamentally, an image sensor is a photon counter - counting photons, which are the smallest units of light energy, that reach it.
There are two main types of image sensors: Charge-Coupled Devices, or CCD, and Complementary Metal-Oxide Semiconductors (CMOS). Each has certain advantages and disadvantages, but the way they function is similar. The material of the sensor is a type of semiconductor material. One key property of semiconductors is the ability to act as a switch In the case of image sensors, when a photon of light reaches the surface of the sensor, it causes the charge on that sensor element (i.e. pixel) to increase slightly. Every photon that reaches it will have the same effect. When a picture is taken, the sensor is exposed to the light source, and then, when done, the level of charge on the element is counted and recorded.
An image sensor in a camera is essentially a collection of individual elements like this, known as pixels, each of a given size, arrayed in a grid. When the picture is taken, the processing circuit on the sensor reads each pixel value and records it in a data structure which is then saved to a disk or removable medium as a file.
