There are many important tools in Astronomy, but nothing is more valuable than a camera - in the case of the late 20th and beyond the CCD is invaluable. It all comes down to what our eyes can perceive. Our eyes are great for day to day activity, but to scrutinize faint object looking through a telescope, our eyes are the last choice. Our sensory retina is just not designed for such tasks.

Gaseous appearance of nebula and galaxies are evident when viewing with the eye, but chances are the image will be mono-chromatic - one color. The larger the telescope, the discerning a particular object may be, but the vivid color is just not there. All of the pretty Hubble images or images in magazines of celestial objects are captured via long period exposures.

There are basically two methods of photography today: film and CCD. Film based photography reigned supreme in regards to field of view. The CCD chips in the early days covered may a few degrees of sky at one time while plate film covered as much as 14 degrees at one time. As CCD's grew larger, cheaper, and better, CCD's have proven to be the workhorse for astrophotography. The reasons are simple:

• CCD's (Charged Coupled Devices) are linear in response - meaning that twice the exposure means twice the signal; film is not
• There are no chemicals required
• CCD image is ready almost immediately, film must be developed (and sometimes the image may not be what was intended)
• CCD's store numerical data so numerous data analysis can be performed without damage to the original; film could be scanned, but that uses pricey drum scanners

CCD's are not without their share of problems - computer error, heat, noise - but most of these errors can be removed by data reduction methods. The Astrophotography Advanced Topics has a project paper I wrote that uses these data reduction techniques.

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