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Calibration (Dark) frames are also an electronic portrait of the camera and contain the Bias, but also
include artifacts, such as hot pixels, which appear over the length of longer exposures. When a master
Dark frame is subtracted from individual Light frames, noise and hot pixels are greatly reduced, making
for a clean, master Light frame. When selected, Start Imaging will take “Darks” with Nightscape’s
shutter closed to prevent any light from falling on the sensor. Darks should also match Light frames in
resolution (binning) and temperature but also exposure duration. Consider taking at least as many
Darks as Lights, with a minimum of 12 frames preferred. Both Bias frames and Dark frames can often
be reused for subsequent Stack sessions.
Calibration (Flat) frames are an optical portrait of the telescope/lens and other elements in the light
path. They are useful for balancing uneven field illumination (UFI), including vignetting, gradients
and for eliminating dust “donuts” (motes) on glass surfaces. When selected, Start Imaging will open
Nightscape’s shutter to acquire Flat frames. Flats are harder to produce correctly and additional study
is suggested. Ron Wodaski’s The New CCD Astronomy is recommended reading. The idea is to image
an evenly lit field (the sky at twilight, lightbox, EL panel) using the same focus, angular camera position
and resolution (binning) as the Light frames, at an exposure time to achieve one-third to one-half of the
saturation level of the camera, perhaps 20k-40k ADUs (Analog to Digital Units). This can be measured
with the cursor, noting the intensity value “i” near the lower right corner of the main frame. Once an
image has been color converted (with Show Full Color or STACK), intensity values are expressed in R, G,
and B. Consider taking a minimum of 9 frames. You may find your optical system is more forgiving than
some and Flats can be skipped. You may even replace them with post processing methods beyond the
scope of AstroFX. To learn of these and other techniques, we recommend Intermediate Part-1 tutorials
by IP4AP.com.
Exposure duration (sec) is the desired length of the exposure(s) in seconds.
Number of exposures is the desired amount of exposures.
Resolution changes the binning modes – Full (1x1), Half (2x2), and Quarter (4x4, for 10100 model only).
Note that the NightScape 8300 produces color images in full (1x1) resolution only. The NightScape 10100
produces color images in all resolution/binning modes.
Subframe is useful for focusing and for applications where you do not need the entire frame. Select Set with
Mouse from the pull down menu and draw a rectangle around a star or section of a downloaded image, or
choose Central Half or Central Quarter from the drop down menu. Only that portion of the sensor will be
downloaded next at a much faster rate than the entire frame. Be sure to set this back to Full Frame before
the imaging sequence if that is your intention.
Object name assigns the target’s name (e.g., M42) to the file and to the FITS header.
Helpful Hint – The Flexible Image Transport System is the standard format for astronomical image
files. A nice feature is the text header which stores information about the image, including: capture
time,temperature, exposure duration, etc. Freeware for reading the header is available from
http://heasarc.gsfc.nasa.gov/ftools/fv.
Root Image Folder is where downloaded files are automatically saved. By default this is C:\Users\Windows\
Documents\AstroFX\Images (Windows 7), but it may be changed to a location of your choice using the
navigation button at right.
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