|
This section takes you through the most basic procedures for taking CCD
images with CCDOPS. The only techniques employed are taking single
exposures and taking dark frames. Using only these techniques you can take
very impressive CCD images of many objects. More advanced techniques are
covered in the following section.
Grab
Once you have focused the telescope and
found your target, the easiest way to capture
an image is using the Grab function. Click the Grab button on the toolbar
or select Camera > Grab from the main menu.
Above: The CCDOPS Toolbar.
In the Grab window, select an exposure time. The exposure will be
limited by the accuracy of the telescope's drive motor and the focal length of
the telescope. The longer the focal length, the shorter the exposure will
need to be to keep the stars in the image from trailing. 30 to 60 seconds
is a reasonable starting point for most telescopes.
Note: Self-guided CCDs can take
much longer exposures, but the techniques involved are more advanced so they are
covered in the Advanced Imaging
section.
Tip: When first using your CCD
system, try taking longer and longer exposures until you see trailed star
images, then use the longest exposure time
without trails. For example, if 60 seconds produces trailed stars but 45
seconds leaves the stars sharp, use 45-second shots. Later you will be
able to stack multiple exposures to achieve the effect of a single longer shot.
Select Also from the Dark Frame pull-down menu, make sure image size
is set to Full and Special Processing is None. Click OK
to take the image.
CCDOPS begins by closing the shutter and taking a dark frame which
will be subtracted from the light exposure to remove noise. Later you may
wish to do this manually, but for now using the Auto feature is most convenient.
You will see an status bar indicating the progress of the exposure.
Once the image is completed it will be downloaded (Auto dark frames are not
displayed).
Download time will depend of the camera and the connection type being used
(parallel, USB, etc.) but typically will be 15 seconds or less. Next, the
Clear filter is selected and the light exposure is taken with the shutter open.
Once downloaded, the final exposure (automatically dark-subtracted) is
displayed. Simple enough!
Note: You can use the Grab
technique to take as many individual images as you like, but you will need to
use another program such as MaxIm DL to combine them.
Color Grab
The simplest way to take a color image with CCDOPS is using the Color Grab
function. Select Grab from the toolbar or Camera > Grab from the
main menu. Set the Grab window parameters as above but change Special
Processing to Color Grab.
When you click OK the Color Grab Setup window appears. This
allows you to set the file names and directory for the three images which will
be taken. The images are saved as separate files and then combined later
to form a color image.
Begin by clicking on Set Name/Dir and choose a name for the files (one
name suffices as each file is appended with either an R, G, or B to indicate
which filter was used to take the image). Leave file type as Compressed.
Set the desired exposure time in the Red exposure field. If you wish for
the Green or Blue exposures to be different you may change the multipliers to
alter the exposure times (for example, a 60-second red with a 1.5 Blue
multiplier results in a 90-second blue exposure). Most often the
multipliers are left set at 1. Click OK to begin taking the images.
Tip: Make sure Reuse dark frames
is set to Yes in the camera setup (Camera > Setup or
Setup on the toolbar). This means only one dark frame is
taken for exposures of the same length (eliminating two exposure from the Color
Grab sequence).
A dark frame is taken first. Then the Red filter is selected, an
exposure is taken and then displayed on screen. Next, the green and blue
exposures are taken, and as each one is displayed the previous image disappears.
Each image has automatically been saved.
Be sure to visit the Image Processing with
CCDOPS section to see how to combine these images to create a color picture.
Next, Advanced Imaging....
Next Page
|
