Specifications

SBIG STF-8300 Manual
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the frame rate or screen update rate can be increased significantly by using
Planet mode. In Planet mode the Focus command takes a full image and
then lets you position a variable sized rectangle around the star. On
subsequent images the Planet mode only digitizes, downloads, and displays
the small area you selected. The increase in frame rate is roughly
proportional to the decrease in frame size, assuming you are using a short
exposure.
The telescope focus is best achieved by maximizing the peak value of
the star image. You should be careful to move to a dimmer star if the peak
brightness causes saturation. The saturation levels of the various resolution
modes are shown in Table 3.2 below. Another point you should also be
aware of is that as you approach a good focus, the peak reading can vary by
30% or so. This is due to the fact that as the star image gets small, where an
appreciable percentage of the light is confined to a single pixel, shifting the
image a half a pixel reduces the peak brightness as the star's image is split
between the two pixels. The Kodak CCD pixels are so small that this is not
likely to be a problem.
Resolution Saturation Counts
High Res ~65,000
Med/Low Res ~65,000
Once the best focus is found, the focusing operation can be greatly
shortened the second time by removing the camera, being careful not to
touch the focus knob, and inserting a high power eyepiece. Slide it back and
forth to find the best visual focus (don’t touch the focus knob), and then
scribe the outside of the eyepiece barrel. The next time the camera is used
the eyepiece should be first inserted into the tube to the scribe mark, and the
telescope visually focused and centered on the object. At f/6 the depth of
focus is only 0.005 inch, so focus is critical. An adapter may be necessary
to allow the eyepiece to be held at the proper focus position. SBIG sells
extenders for this purpose.
Finding and Centering the Object
Once best focus is achieved, we suggest using Full-Low mode to help
center objects. This mode gives a full field of view, but reduces resolution
in order to increase the sensitivity, and digitization and download rate. If
you have difficulty finding an object after obtaining good focus, check to be
sure that the head is seated at best focus, then remove the head and insert a
medium or low power eyepiece. Being careful not to adjust the focus knob
on the telescope, slide the eyepiece in or out until the image appears in good
focus. Then visually find and center the object, if it is visible to the eye. If
not, use your setting circles carefully. Then, re-insert the camera and use
the Focus Mode with an exposure time of about ten seconds, if the object is
quite dim. Center the object using the telescope hand controls.