Sky and Telescope - March 2016 - 69

CURTIS MACCHIONI (2)

COLORFUL RESULTS Astrovideo observing is primarily geared toward revealing faint targets on your video monitor. These images of M20, the
Trifid Nebula (left), and the spiral galaxy M33 are typical of what to expect with a color camera and moderate aperture.

Helpful Settings
Unless you're operating your camera with
a computer, you'll need to access the camera's on-screen display (OSD) to adjust its
menu settings. While each camera's OSD
menu is slightly different, they all have
the same general functions. The most
important functions you'll change the
most are Exposure, AGC (Automatic Gain
Control), and Gamma. If your camera has
a color chip, then you'll also have a White
Balance setting.
Exposures are typically divided into
two or three categories: 1/100 -second or
shorter exposures are best for solar, lunar,
and planetary viewing. Shutter speeds
of up to 2 seconds are most useful when
focusing or adjusting your Go To pointing alignment, and they can even aid in
collimating your telescope. Images of 3
seconds or longer are best for viewing
deep-sky objects and the occasional nearEarth asteroid.
The AGC setting is similar to the ISO
value on a DSLR camera. It increases the
amplifier gain, thereby increasing image
detail and reducing the required exposure time. But this comes at the expense

of increased noise in your video, as well
as noticeable "amp glow," caused when
infrared radiation emitted from the readout amplifier is picked up by the camera's
detector. Amp glow appears as a bright
background at a corner or top of the video
image, and it's more noticeable when
using high-gain settings, long exposures,
or a combination of both.
Gamma adjustments allow you to
stretch the luminosity values in the
image, which increases detail (but
reduces contrast). A setting of 1 produces
an unenhanced image, while lower values
enhance fainter nebulosity but lighten the
overall background of the video.
In a color camera, White Balance
allows you to adjust the color balance
in your video. Usually you're offered
options for automatic or manual modes.
In automatic mode, the camera adjusts
the color to what it assumes is optimal;
in manual you set the red and blue levels
of the video feed until the image appears
properly balanced.
Two other important settings are
Brightness and Contrast, which are
usually adjusted on the monitor itself
or within the video-capture software.
Brightness raises or lowers all parts of
the image from dark to light equally. The
Contrast setting changes the slope of
the light curve from black to white while
keeping the black point fi xed, reducing
the dynamic range of the image.

Under the Stars
Once you've geared up, here are some tips
to start observing. After replacing your
telescope's eyepiece with the astrovideo
camera, be sure to secure the power and
control cables to prevent snags when
slewing to targets around the sky.
Start by focusing on a bright star
with the Exposure set at about 2 seconds,
Gamma at 0.3, and AGC at the midpoint;
this should produce a bright image that
refreshes quickly. Once focused, slew to a
DSO of interest and take a test exposure
of 10 seconds or so, depending upon the
surface brightness of your target. Adjust

ROD MOLLISE

While not essential, a light-pollution
filter can make a big difference in what
you can see from typical light polluted
sites. An infrared "cut fi lter" will also
block unfocused infrared light to produce
smaller stellar images.

EXPANDED VIEW One benefit of the small
detectors in astrovideo cameras is their ability
to utilize strong focal reducers without producing objectionable distortions in stellar images.
This allows you, for example, to convert your
f/10 SCT into a fast f/3.3 wide-field instrument.

Sk yandTelescope.com March 2016

69


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Sky and Telescope - March 2016

Table of Contents for the Digital Edition of Sky and Telescope - March 2016

Contents
Sky and Telescope - March 2016 - Cover1
Sky and Telescope - March 2016 - Cover2
Sky and Telescope - March 2016 - 1
Sky and Telescope - March 2016 - Contents
Sky and Telescope - March 2016 - 3
Sky and Telescope - March 2016 - A
Sky and Telescope - March 2016 - B
Sky and Telescope - March 2016 - 4
Sky and Telescope - March 2016 - 5
Sky and Telescope - March 2016 - 6
Sky and Telescope - March 2016 - 7
Sky and Telescope - March 2016 - 8
Sky and Telescope - March 2016 - 9
Sky and Telescope - March 2016 - 10
Sky and Telescope - March 2016 - 11
Sky and Telescope - March 2016 - 12
Sky and Telescope - March 2016 - 13
Sky and Telescope - March 2016 - 14
Sky and Telescope - March 2016 - 15
Sky and Telescope - March 2016 - 16
Sky and Telescope - March 2016 - 17
Sky and Telescope - March 2016 - 18
Sky and Telescope - March 2016 - 19
Sky and Telescope - March 2016 - 20
Sky and Telescope - March 2016 - 21
Sky and Telescope - March 2016 - 22
Sky and Telescope - March 2016 - 23
Sky and Telescope - March 2016 - 24
Sky and Telescope - March 2016 - 25
Sky and Telescope - March 2016 - 26
Sky and Telescope - March 2016 - 27
Sky and Telescope - March 2016 - 28
Sky and Telescope - March 2016 - 29
Sky and Telescope - March 2016 - 30
Sky and Telescope - March 2016 - 31
Sky and Telescope - March 2016 - 32
Sky and Telescope - March 2016 - 33
Sky and Telescope - March 2016 - 34
Sky and Telescope - March 2016 - 35
Sky and Telescope - March 2016 - 36
Sky and Telescope - March 2016 - 37
Sky and Telescope - March 2016 - 38
Sky and Telescope - March 2016 - 39
Sky and Telescope - March 2016 - 40
Sky and Telescope - March 2016 - 41
Sky and Telescope - March 2016 - 42
Sky and Telescope - March 2016 - 43
Sky and Telescope - March 2016 - 44
Sky and Telescope - March 2016 - 45
Sky and Telescope - March 2016 - 46
Sky and Telescope - March 2016 - 47
Sky and Telescope - March 2016 - 48
Sky and Telescope - March 2016 - 49
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Sky and Telescope - March 2016 - Cover3
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