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Astrophotography - Professional Photography

Astronomer's primarily use CCD's for image capture. In the years past, the champion of professional photography is Astronomy was the photographic plate - a specialty item of fine grain film using glass instead of gelatin as a base. This eliminated any image errors as a result of creases in the gelatin and allowed for larger frames to be constructed. The typical field of view of a photographic plate is an incredible 14 degrees.

Many of the larger manufacturers like Kodak are abandoning production of professional plate film. This has little bearing in Astronomy as the CCD has been embraced as the imager of choice. Professional images look rather boring, mostly because the professional is interested in a different type of photograph. While amateurs will take various images through different color filters for the purpose of combination to a color image, the professional also takes various images through filters but only to study each individual image. Professional photography consists of:

  • Photometric analysis - images through UVBRI filters (Ultraviolet, Visual - Green, Blue, Red, and Infrared) to study magnitudes of stars in each frame
  • Wide field photography for supernova searches
  • Wide field imagery for all-sky imagery
  • Photography is star and galaxy spectra

Image processing is a bit different for the professional. Advanced CCD's have a region of the chip called the overscan region:

This region of the CCD provides vital calibration data for the image.

Astronomers prefer images with a wide field of view. Since plate film is not used, CCD's must be constructed to allow for wide field photography.

Professional CCD's are often custom made camera culminating of several CCD chips called a mosaic. This particular mosaic is used on the Canada-France-Hawaii Telescope. A CCD mosaic can be as large as 40 2,048x4,612 pixel chips. In addition, these chips are cooled by liquid helium. Image Credit.

These mosaics provide for a large field of view. Other features of professional CCD's include:

  • Back-illuminated chips - turned over and shaved, the back side of a CCD allows for minimal interference with light but are expensive to make
  • To eliminate noise, cooling is often done with freezing water or liquid hydrogen or helium
  • May include special filtering to allow or eliminate infrared or ultraviolet information

It should be noted that amateur CCD's are quickly approaching professional standards. As such, many amateur astronomers are using these CCD camera to provide valuable data for professionals. Amateur CCD makers include (but not limited to):

These manufactures use specialty Kodak and SITe CCD's in a variety of formats, including back illuminated and research grade applications.

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