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(Although the telescope is pointing at a featureless
surface, the focus and orientation must be set as it
normally would be for astro-images.)
3.
Set the Frame Type in your imaging control program to Flat
Field for correct meta data flagging in the fits header.
4.
Set the exposure to result in a histogram which has a
hump at around 1/3 to 1/2 of full exposure.
Import your Darks and Flats into the programs mentioned above
for full image calibration of your astro-photos.
Image Processing
It's not uncommon to use 3-4 programs to tweak the astro-imag-
es you've taken to get the best possible final result. Please delve
into the manuals for the other programs listed above, along with
output for Photoshop, Lightroom, or other standard image pro-
cessing programs. The images taken for this manual and on
telescope.com were all taken using a combination of StarShoot
Image Capture, SharpCap, DeepSkyStacker, and PhotoShop.
Color Conversion (one shot color cameras only)
It was mentioned previously to save the images in the RAW
.fit format, for later processing in 3rd party software. RAW is a
"black and white" format with a "screen door effect" laid over the
image. This screen door is the Bayer Matrix, and contains the
color data. When you convert the RAW format to a color for-
mat, the screen effect disappears and you're left with a full color
image. The preview window in StarShoot Image Capture shows
a color image, but if you set the saved file type to RAW, you will
save an unconverted black and white image in the .fit format.
To convert to color, see the instructions included with the 3rd
party software packages, but you'll have to also determine the X
and Y offset, in order to reproduce correct colors. This is differ-
ent in each software program and usually requires experiment-
ing in order to correctly convert. Color balance may also have
to be adjusted to correctly display the image from a chip that is
most sensitive in Green, and less sensitive in blue. For exam-
ple, in DeepSkyStacker, we found the best setting was "generic
RGGB" for the Bayer matrix filter, and "Bi-linear Interpolation" .
After that, color balance could be used to rebalance the back-
ground levels to a neutral color.
NOTE: the G16 Color Bayer Matrix is arranged GRBG or
BGGR (depending on the software you are using), instead
of RGGB in the others. X and Y offsets are different.
ASCOM Driver
The ASCOM driver allows the camera to be used with any of
the programs listed above, along with any others that support
ASCOM cameras. Please download the ASCOM platform
from ascom-standards.org and make sure to install the camera
ASCOM driver from Orion's website. When in 3rd party camera
control programs, the camera gain settings can be controlled in
the ASCOM setting window for the camera. Open the ASCOM
camera settings, adjust the gain, and experiment with expo-
sures as detailed above. Since stacking reduces noise, it can
be beneficial to have a bit more noise in the image, if it helps
10
keep the exposure times down. One last thing to note, some
programs may use a percentage for gain, others may use the
actual gain numbers. If the gain range is 0-100, it's using a per-
centage of total gain.
G24 Spacing rings
Since the G24 is a full format camera chip, it becomes neces-
sary to use a coma corrector on most Newtonian reflectors, or a
field flattener on refractors in order to optimize the distortion cor-
rection of the telescopes field. Most coma correctors and field
flatteners need to be positioned with 55mm distance between
the chip and the attachment threads on the lens. This 55mm
distance is the default spacing for a DSLR housing, but cameras
such as the G24 have a chip mounted closer to the front open-
ing (17.5mm in the case of the G24). Because of this, we are
providing several spacer adapters that will replace the standard
2" nozzle on your G24 (figure 11). Thread in the 54mm – 48mm
ring first (21mm length), then the 16.5mm extension ring, and
then your coma corrector/field flattener (assuming it has 48mm
t-threads. This will provide 55mm distance between the chip
and the corrector/flattener.
If you have a coma corrector or flattener that uses 42mm
threads, use the 48mm to 42mm zero profile ring to step the
threads down to 42mm. We do not usually recommend this, as
a 42mm opening will vignette the larger chip, and the edges of
your field will become darker.
Please note that the standard 2" nozzle that is included with the
G24 is threaded for Orion filters (M48 x 0.6mm), and does not
use the camera t-thread pitch of 0.75mm. If you wish to add the
extensions or purchase other length extensions online, make
sure to be using the native opening of the camera (M54 x 0.75),
or one of the spacing rings which also provides 0.75mm thread
pitch in either the 48mm or 42mm diameter.
16.5mm extension ring
(48mm x 0.75mm)
48mm to 42mm
stepdown adapter
(zero profile),
0.75mm thread
pitch
Figure 11 The spacer rings included with the G24.
54mm - 48mm reduction adapter (2"
OD, 21mm length)
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