Sky and Telescope - April 2016 - 71
can obtain is limited by atmospheric turbulence, commonly called "seeing."
Small pixels are better suited than large ones to take
advantage of a fast optical system. Conversely, a slow optical system would probably waste the potential resolution
gain provided by smaller pixels (as well as having the disadvantage that less light is delivered to each small pixel).
In an undersampled image, there are too few pixels
for the detail the optics and sky conditions could have
delivered. Conversely, oversampling means you're using
far too many pixels given the resolution capabilities of
your optics or the sky conditions. A super-high-resolution camera will not really deliver more resolution than
your optical system or the local seeing conditions can
deliver; you just get a blurry mess that looks better only
when you shrink it down in Photoshop. Better results are
obtained with proper sampling in the fi rst place. You can
easily determine your sampling resolution with this formula: arcsec/pixel = 206.3 × pixel size / FL (mm). Typical
"average" seeing is about 2 arcseconds.
Parting Thoughts
Selecting a camera for astrophotography shouldn't be
done outside the context of the optics you'll use it with.
In general, cameras with small pixels or color detectors
perform well when paired with fast focal-ratio instruments. While you can certainly use a camera with big
pixels on a fast optical system (which compensates for a
lower QE detector and less-than-perfect guiding), they
also perform very well on slower optics.
In addition to a camera chip's sensitivity, read noise
is the limiting factor when stacking short exposures to
reveal faint detail in deep-sky objects. Cooling provides a
huge boost in performance, but don't obsess over really
deep cooling if you're just getting started.
Finally, I've intentionally neglected to address the
debate over CCD versus CMOS sensors. That's because
there really is no debate, given the current state of the
art. Both deliver great images and perform very well for
astrophotography. CMOS has a definite edge in readout
speed (great for video), while CCDs are more sensitive to
ultraviolet and infrared wavelengths, though this won't
be the case much longer. For normal deep-sky photography I would not let the choice of a CCD or CMOS
detector be a deciding factor when choosing between
two similar cameras.
Just remember, there is no single "best camera."
Consider what you want to image, where you're imaging
from, and how you're collecting the light. Using these
criteria, you can evaluate a camera's specifications and
suitability to your imaging goals. ✦
Richard S. Wright, Jr. is a senior software developer at Software Bisque by day and an avid astrophotographer by night,
imaging deep-sky targets every clear night he can.
UNDERSAMPLING BENEFITS A DSLR with a wide-angle lens
vastly undersamples the night sky, but it's relatively unaffected by
atmospheric turbulence and tracking errors. This image was taken
with a simple sky tracker (Sky-Watcher Star Adventurer) and a
Canon EOS 5D DSLR with a 14-mm f/2.8 lens.
Sk yandTelescope.com April 2016
71
http://www.SkyandTelescope.com
Sky and Telescope - April 2016
Table of Contents for the Digital Edition of Sky and Telescope - April 2016
Contents
Sky and Telescope - April 2016 - Cover1
Sky and Telescope - April 2016 - Cover2
Sky and Telescope - April 2016 - 1
Sky and Telescope - April 2016 - Contents
Sky and Telescope - April 2016 - 3
Sky and Telescope - April 2016 - A
Sky and Telescope - April 2016 - B
Sky and Telescope - April 2016 - 4
Sky and Telescope - April 2016 - 5
Sky and Telescope - April 2016 - 6
Sky and Telescope - April 2016 - 7
Sky and Telescope - April 2016 - 8
Sky and Telescope - April 2016 - 9
Sky and Telescope - April 2016 - 10
Sky and Telescope - April 2016 - 11
Sky and Telescope - April 2016 - 12
Sky and Telescope - April 2016 - 13
Sky and Telescope - April 2016 - 14
Sky and Telescope - April 2016 - 15
Sky and Telescope - April 2016 - 16
Sky and Telescope - April 2016 - 17
Sky and Telescope - April 2016 - 18
Sky and Telescope - April 2016 - 19
Sky and Telescope - April 2016 - 20
Sky and Telescope - April 2016 - 21
Sky and Telescope - April 2016 - 22
Sky and Telescope - April 2016 - 23
Sky and Telescope - April 2016 - 24
Sky and Telescope - April 2016 - 25
Sky and Telescope - April 2016 - 26
Sky and Telescope - April 2016 - 27
Sky and Telescope - April 2016 - 28
Sky and Telescope - April 2016 - 29
Sky and Telescope - April 2016 - 30
Sky and Telescope - April 2016 - 31
Sky and Telescope - April 2016 - 32
Sky and Telescope - April 2016 - 33
Sky and Telescope - April 2016 - 34
Sky and Telescope - April 2016 - 35
Sky and Telescope - April 2016 - 36
Sky and Telescope - April 2016 - 37
Sky and Telescope - April 2016 - 38
Sky and Telescope - April 2016 - 39
Sky and Telescope - April 2016 - 40
Sky and Telescope - April 2016 - 41
Sky and Telescope - April 2016 - 42
Sky and Telescope - April 2016 - 43
Sky and Telescope - April 2016 - 44
Sky and Telescope - April 2016 - 45
Sky and Telescope - April 2016 - 46
Sky and Telescope - April 2016 - 47
Sky and Telescope - April 2016 - 48
Sky and Telescope - April 2016 - 49
Sky and Telescope - April 2016 - 50
Sky and Telescope - April 2016 - 51
Sky and Telescope - April 2016 - 52
Sky and Telescope - April 2016 - 53
Sky and Telescope - April 2016 - 54
Sky and Telescope - April 2016 - 55
Sky and Telescope - April 2016 - 56
Sky and Telescope - April 2016 - 57
Sky and Telescope - April 2016 - 58
Sky and Telescope - April 2016 - 59
Sky and Telescope - April 2016 - 60
Sky and Telescope - April 2016 - 61
Sky and Telescope - April 2016 - 62
Sky and Telescope - April 2016 - 63
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Sky and Telescope - April 2016 - 65
Sky and Telescope - April 2016 - 66
Sky and Telescope - April 2016 - 67
Sky and Telescope - April 2016 - 68
Sky and Telescope - April 2016 - 69
Sky and Telescope - April 2016 - 70
Sky and Telescope - April 2016 - 71
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Sky and Telescope - April 2016 - 73
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Sky and Telescope - April 2016 - 76
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Sky and Telescope - April 2016 - 78
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Sky and Telescope - April 2016 - 81
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Sky and Telescope - April 2016 - 84
Sky and Telescope - April 2016 - Cover3
Sky and Telescope - April 2016 - Cover4
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