22
23
7. Select the file folder in which you
would like to save the images with
Select Image Save Path found by
clicking the arrow in the
Autosave
Setup window (Figure 18.2)
and set the name of the file in
Autosave Filename. Typically the
name of the object being imaged,
such as “OrionNebula1”, will be
entered here. If “OrionNebula1”
is the
Autosave Filename,
and you choose to save five
images, then the images will
appear in the selected file
folder as “OrionNebula1_0001.
fit”, “OrionNebula1_0002.
fit”, “OrionNebula1_0003.fit”,
“OrionNebula1_0004.fit”, and
“OrionNebula1_0005.fit”. Try
exposures of 30-60
Seconds to
start.
8. Click
Expose, and the camera will commence taking the images.
Note: When the camera is taking long exposure images, it is critically important
not to touch, shake, or otherwise disturb the telescope, or a blurred image will
result. Also, make sure no surrounding light shines into the telescope during the
exposure.
Dark Frames
Dark frames are images taken with no light coming into the camera. A dark frame
is typically taken with the telescope’s objective capped. The only data in the image
is the inherent camera noise (Figure 19). The noise contains the dark current
(background noise level), read noise (noise introduced during camera readout and
download) and hot pixels (bright dots in the image). All of this noise exists in your
raw astro-image too, which distracts from the detail you want to see.
To eliminate most of the camera noise, you can take several dark frames, average
them, then subtract them from your astro-images, also called, “light” images.
Note: Make sure the cooler set point and CCD temperature are the same as they
were when you took your light frames.
To take dark frames for subtraction from “light” images:
1. Set the
Frame Type in the Camera Control Window’s Expose tab to Dark.
Or if you are taking a sequence of images, set the
Type in the Autosave
Setup window to Dark (Figure 20). Even though MaxIm DL will already know
which of your images are dark frames, it’s a good idea to assign a preset,
such as
D to better organize your different images.
Note to Parsec 8300C and 10100 users: You must take Raw Light frames in mono-
chrome BEFORE converting to color in order to utilize dark frames.
2. Use the same exposure time as the “light” images you have or will take. If
your “light” image is 60 seconds, the dark frame must also be 60 seconds.
3. Set the number of dark frames you would like the camera to take under (3 to
10 will generally suffice, as these will be averaged together).
4. Click
OK, and proceed to click Expose in the Expose tab
.
Since the Parsec
has a shutter, you to not need to be present when the dark frames are taken,
it will occur automatically during the sequence!
Figure 18.2.
Select
Set Image Save Path.
Figure 19.
A dark frame contains the
thermal and background noise, as well as
any read noise. The same noise appears
in your “light” images. Dark frames isolate
the noise so it can later be subtracted from
your “light” images.
Figure 20.
Set the
Type to Dark in the Autosave Setup window.
