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.
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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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