CCD imaging

This chapter will deal with the most basic use of a CCD, that of direct imaging. We will discuss a few more preliminaries such as flat fields, the calculation of gain and read noise for a CCD, and how the signal-to-noise value for a measurement is determined. The chapter then continues by providing a brief primer on the use of calibration frames in standard two-dimensional CCD data image reduction. Finally, we cover some aspects of CCD imaging itself including applications of wide-field imaging with CCD mosaics and CCD drift scanning.

4.1 Image or plate scale

One of the basic parameters of importance to a CCD user is that of knowing the plate scale of your image. Plate scale is a term that originates from when photographic plates were used as the main imaging device and is often given in arcsec/mm. For a CCD user, however, a more convenient unit for the plate scale is arcsec/pixel. Clearly the conversion from one to the other is simple. The focal ratio of a telescope is given by focal length of primary mirror primary mirror diameter '

where both values are in the same units and "primary mirror" would be replaced by "primary objective lens" for a refractor. Taking the focal length of the primary (f) in mm and the CCD pixel size (u) in microns, we can calculate the CCD plate scale as

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