Methods

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Collecting Electromagnetic Information
Methods Eye (visible window) Camera film
Camera CCD (Digital)
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Collecting Electromagnetic Information
Eye (visible window) Advantages Everyone wants
to see objects directly Disadvantages Light
gathering capability can see without telescope
down to magnitude 6 Image cannot be stored Cannot
do a time exposure
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Collecting Electromagnetic Information
Camera film Discussions of film ended in
08/WI Digital cameras have become affordable and
high resolution
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Collecting Electromagnetic Information
Camera CCD (Digital) Advantages Resolution Can
do a time exposure Can store directly to a
computer Can be manipulated Short Exposure
Times Disadvantages Expense but not
bad Pixilated Image
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Collecting Electromagnetic Information Digital
Image
Peter Powers Department of Physics 6 in Compound
Telescope Motor drive
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Collecting Electromagnetic Information Digital
Processing
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Collecting Electromagnetic Information Digital
Processing
Layer and Flatten
Raw
Duplicate and Blur
Invert
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Collecting Electromagnetic Information Digital
Processing
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Collecting Electromagnetic Information Digital
Processing
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Comparison Film vs CCD
The Advantages of CCD Imaging Professional
astronomers have been using CCDs for nearly two
decades and have no thoughts about going back to
film.  The advantages are impressive CCD
cameras are up to 100 times more sensitive than
film CCD images are digital, meaning no
film-processing, scanning, scratching, or fading
CCD cameras have a much greater dynamic range
than film, meaning they can more easily capture
both faint and bright detail in a single exposure
CCDs are capable of resolving finer detail
than film (this can, however, be limited by the
telescope used and the atmospheric conditions)
For the amateur, several other advantages apply
as well Taking images with a CCD is
generally much easier than with film Learning
goes faster due to the ease-of-use and shorter
exposure times Light pollution is less
obtrusive and more easily removed from CCD
images, meaning imaging from a backyard site is
more likely to be possible with CCD
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Comparison Film vs CCD Efficiency and Exposure

• Efficiency
• A CCD can record as much as 90 of the
  incident photons
• Film will record less than 5 of the incident
  photons
• CCD will record object 10 to 20 times fainter
  than film with the same exposure time
• Exposure Times
• CCD can record the same image with less than
  one tenth of the exposure time for film

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Comparison Film vs CCD Exposure
Above  On the left is a CCD image taken from a
suburban location.  The exposure time is about 30
minutes.  On the right is a film image of the
same object taken using a similar telescope.  The
exposure time is over 2 hours and the level of
detail is far less than the CCD image.  At full
resolution the difference is even more impressive.
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Photometry
Photometer An instrument which measure the
brightness of an object Will measure the TOTAL
brightness of an object, which might be difficult
to interpret. However, when combined with
filters, can be used to measure the amount of
light produced over a narrow range of
frequencies. This can be compared with standard
Blackbody radiation curves to determine the
temperature of the object
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Photometry
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Photometry
Photometer An instrument which measure the
brightness of an object Will measure the TOTAL
brightness of an object, which might be difficult
to interpret. However, when combined with
filters, can be used to measure the amount of
light produced over a narrow range of
frequencies. This can be compared with standard
Blackbody radiation curves to determine the
temperature of the object
Intensity
X
X
X
Wavelength
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Photometry
Photometer An instrument which measure the
brightness of an object Will measure the TOTAL
brightness of an object, which might be difficult
to interpret. However, when combined with
filters, can be used to measure the amount of
light produced over a narrow range of
frequencies. This can be compared with standard
Blackbody radiation curves to determine the
temperature of the object
Temperature of object is 7000 K
Intensity
X
X
X
Wavelength
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Spectroscopy Revisited
Spectroscopes can be used to analyze the image
through the eyepiece. The spectra can then be
viewed with the eye, a camera, or a CCE for
analysis.