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Film astrophotography began in the late 19th century with photographs of the
moon, sun, and bright stars. Film then was thousands of times slower than
it is today. While film became faster and faster, the technology itself
changed very little. Then, in the 1970s, professional astronomers began
using CCD cameras instead of film. Eventually, CCDs became more readily
available for amateur astronomers. As CCDs become less expensive, they are
becoming more popular and have all but completely overtaken film for
astrophotography. Digital cameras for regular photography have also
supplanted most film use, so the natural question to ask is whether
astrophotography can be done with a regular digital camera. The answer is
yes, but there are advantages to both types of imaging.
Note: Since only
digital SLRs are practical for deep-sky imaging, this discussion is limited to
that type of camera. See the Digital Cameras
section for a comparison of point-and-shoot digicams and DSLRs.
The Advantages of CCD Imaging
The primary advantage of CCD imaging is sensitivity.
The more sensitive the camera, the shorter the exposure required to detect faint
detail.
Above: The Veil Nebula imaged with a CCD
camera from light-polluted suburban skies. Six 5-minute exposures with a
HyperStar C14.
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CCD cameras are up to 50 times more sensitive than standard
digital SLRs
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CCD cameras have a greater dynamic range than digital SLRs, meaning they can
more easily capture both faint and bright detail in a single exposure
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Most (but not all) CCDs have a linear response, which means
they can be used for photometry--studying the brightness of objects such as
variable stars or asteroids
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The shorter exposure times required by CCDs means learning
is easier
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The fast exposures also mean that most of the time less
equipment and hassle will be required
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For setups where guiding is required, some CCD cameras have
built-in guide chips to make guiding much easier
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Less hardware may be required for CCD imaging, depending on
the setup (see below)
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Greater sensitivity makes imaging through filters
(narrowband or light pollution filters) easier
The Advantages of Digital SLRs
The biggest advantage of using a digital SLR is cost (with
some notable exceptions discussed below). The larger the chip is in a CCD
or DSLR, the more the camera will cost (all else being equal). For a given
size chip, a DSLR will cost less than a CCD. This is due to several
reasons. CCD chips are much more sensitive, they have fewer pixel defects,
they have less noise, and the cameras often feature thermoelectric cooling to
reduce noise even further. DSLRs are mass produced, so economies of scale
come into play. Canon has sold over 1 million of its EOS Digital Rebel XT
cameras. So the camera itself is less expensive, although with some
setups, more extraneous hardware may be required.
Above: Image of the Lagoon Nebula region with
a Canon EOS 20Da (enhanced DSLR). Single 20-minute exposure through a
300mm f/2.8 lens. Image by James McGaha.
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Cameras are less expensive for a given size chip and number
of megapixels
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A digital SLR can be used for other purposes such as
photographing your vacation, your cats, your new telescope, etc.
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A larger chip means a larger field of view, and more pixels
means larger printed photos
More About
Price
While a digital SLR may cost less than a comparable (in terms
of chip size and pixel count) CCD camera, the overall cost may not be less for a
DSLR. The best example is HyperStar imaging. A very common setup
would use an 8" Schmidt-Cassegrain telescope. For DSLR imaging of deep-sky
objects, this setup will also require an equatorial wedge, focal reducer,
guidescope, guide camera, mounting rings and dovetail plate, and counterweights.
This extra hardware would cost around $1500. For CCD imaging the only
extra hardware needed would be the HyperStar lens. The savings is nearly
$1000, which will likely make up for the difference in cost of the cameras.
Not to mention an equivalent exposure would be around 50 times shorter!
Return to Introduction to CCD Imaging
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