Orion 52083 - Manual (Page 40)

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1. In the Camera Control Window, select Light 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.