Specifications
possible to distinguish which part of the nebula is emission (red) and which
is reflection (blue). But astronomical cameras are only rarely equipped with
color CCD chips from number of reasons. The color and monochrome chips
are discussed in the SIPS User's Guide – refer to the “Introduction to CCD
Imaging” chapter.
Although the G3 camera is equipped with monochrome CCD chip, it is
definitely capable to capture color images, at last when the internal filter
wheel contains RGB filters. Instead of shooting single color image, three
images – each for Red, Green and Blue colors, must be obtained and
combined. This process is not suitable for fast moving/changing objects, but
astronomical objects usually do not change so fast.
Taking three images and combining them is undoubtedly more complex
procedure than shooting simple color image. But using of monochrome chip
brings so important advantages for astronomical usage, that bothering with
multiple images is definitely worth the effort:
● Color CCD chips have one fixed set of filters without the
possibility to exchange them or to completely remove them.
Monochrome chip is capable to take images with narrow-band
filters like Hα, OIII, etc.
● Color chips have less Quantum Efficiency (QE) then monochrome
ones. Limiting QE from around 80% to around 30% by color filters
only wastes light in number of applications.
● Interpolation of pixel luminance from surrounding pixels,
necessarily performed when processing images from color chips,
introduces significant error and prohibits precise measurement of
position (astrometry) and brightness (photometry).
● Color CCD chips do not allow reading of binned images.
● Color CCD chips do not allow so-called Time Delay Integration
(or Drift-Scan Integration).
Another huge advantage of monochrome chip is the possibility to combine
color images from three color images and one luminance image. Luminance
image is captured without filter, using maximum chip sensitivity. This
technique is often called LRGB imaging.
Inserting the color filter into the light path significantly reduces the amount
of light captured by the chip. On the other side the human eye is much less
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