Orion 52080 - Manual (Page 20)

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Focusing
One of the hardest things to do in imaging is achieving good focus. You can
simply watch the computer screen to focus (Focus in the Camera Control
Window), but you can focus “by the numbers” on a bright star to get the best
focus possible. To do this:
1. In the Camera Control Window, select Light Raw 1x1 mode.
2. Set the exposure time to 1 to 5 Seconds, depending on how bright the star
is.
3. Turn off Dark Subtract.
4. Now beneath the Mode selector, pick Focus, and then click Expose. The
camera will take repeated exposures, until you click Stop.
5. Point the telescope at a bright star, and you can focus “by the numbers”:
• MaxPixel is the value of the brightest pixel in the image. When you are
in focus, it will be at its highest value. You will need to look at the value
for several images in succession, because the number will bounce around
with the seeing.
Note: If the MaxPixel reaches 65535, the image is saturated and all three focus
numbers will be inaccurate. Either pick a fainter star, adjust the camera’s
Analog Gain settings using the Setup button, or use a shorter exposure time.
• FWHM, or Full-Width Half Maximum, is the width of the star half-way
down the sides. This provides a highly accurate measurement when you
are close to focus. When you are at focus, it will be at its lowest value.
This number will vary due to seeing, so it is best to look at several images
before decided.
• HFD, or Half Flux Diameter, is similar to FWHM, but works much better
than FWHM when the star is badly out of focus. It can produce a usable
number even when the star looks like a donut.
Refocus often throughout your imaging session. This ensures at least some
of your images will have an excellent focus. It is also not uncommon for tele-
scope motions or movements to alter the focus slightly, so be sure to refocus
after slewing to any new astro-imaging targets.
Choosing a Site for Astro-imaging
Once you have a focused image, you may find your image shifting and washed
out. This can be caused by many environmental factors. Poor seeing (move-
ment of molecules in the air, such as heat rising) and poor transparency (mois-
ture, smoke, or other sky contaminants) will all serve to reduce image quality.
That is why most major astronomical telescopes are on high mountains in thin
air, to get above much of the transparency and seeing problems. Also, wind
will move your telescope and affect images. Your eyes viewing through an
eyepiece can change slightly to compensate for disturbances like these, but
the camera can not. Keep these factors in mind when choosing an observing
site for astronomical imaging.
For the best astro-images, we recommend finding a location with dry air, some
altitude, and away from city or streetlights. Even a nearby hilltop in the coun-
tryside can provide better viewing conditions than many convenient backyard
locations.
Loss of Camera Connection
If the computer connection to the camera is interrupted, you will need to
re-establish connection. This can happen due to several reasons; if a cable
becomes unplugged, the computer “freezes”, or the software/hardware other-
wise temporarily loses the data coming from the camera.
To re-establish camera connection, first close the Maxim DL Essentials pro-
gram on your computer. Then, unplug and re-plug the camera into the com-
puter’s USB port. Now, open Maxim DL Essentials, and the Camera Control
Window should appear indicating re-established connection between camera
and computer.
Using Focal Reducers and Barlow Lenses
Focal reducers and barlow lenses change the effective focal length of a tele-
scope. These lenses are inserted between the camera and telescope when
imaging to change image scale.
Focal reducers serve to decrease the focal length of your telescope. This
increases the field of view seen by the camera (decreases camera magnifi-
cation). This can be very useful for obtaining images of wide-field deep sky
objects, such as the Andromeda Galaxy or the Pleadies star cluster. Focal
reducers will usually thread onto the nosepiece of the SSDSI-II.
Barlow lenses increase the focal length of your telescope, which makes the
camera’s field of view narrower (increases camera magnification). This is useful
for planetary imaging. Keep in mind that when the focal length is doubled, the
image will become four times dimmer, so a longer exposure may be necessary.
Barlow lenses are generally inserted in the focuser’s drawtube and secured
with the thumbscrew on the focuser’s drawtube, and the SSDSI-II’s nosepiece
is inserted into the barlow and secured with the thumbscrew on the barlow
lens.
Filters
Any standard Orion 1.25" filter will thread into the front of the SSDSI-II’s barrel.
For some types of planetary imaging, you may want to use color filters to bring
out subtle details. Try using several different color filters on a planet to see
which filters help best show planetary details.