16
8. In the
Camera Control Window
, in the box below the
Mode
box, select
Focus
. Click
Expose
. The camera will only download the area you previ-
ously selected, which makes each image download significantly faster than
the whole frame.
Note: If the StarShoot Pro is grossly out of focus, no object will appear in the
image, not even a blur. Increase the exposure time if needed and patiently
move through the focus range of your telescope until you see the centered
star come into view.
9. Gradually adjust the telescope’s focuser inward until the star visually
comes to a small point on your computer screen. You have achieved a
rough focus. Some small adjustments remain to get a perfect focus.
10. Click the
Stop
button.
11. Set
Seconds
somewhere between 0.002 and 0.1 seconds (or longer for
fainter stars).
12. Click
Expose
.
13. Carefully watch the
FWHM
and
Max Pixel
values in the
Camera Control
Window
(Figure 11). The
FWHM
(Full-Width Half Maximum) indicates the
diameter of the star. The
Max Val
is the brightness value for the brightest
pixel in the star. The smaller the
FWHM
, and the larger the
Max Pixel
, the
closer you are to focused.
14. Adjust the focus as needed to get the smallest
FWHM
and largest
Max
Pixel
possible. The
Max Pixel
should stay well below 65535, as this is the
saturation level for the camera. If the
Max Pixel
approaches 65535, reduce
the exposure time or try selecting a fainter star. Paying attention to these
values will help you get a very accurate focus, far better than simply look-
ing at the star image on your screen.
15. Click
Stop
once you reach the best focus and click
Reset
in the
Subframe
section at the bottom of the
Camera Control
window (Figure 12). Before
proceeding to take images, set the
Mode
box back to
Single
.
Note: Due to atmospheric seeing conditions, you may notice significant fluc-
tuation in the
FWHM
and
Max Pixel
values while focusing. You typically have
to take multiple exposures each time you adjust the focuser to determine the
quality of your focus.
Figure 11.
The
FWHM
and
Max Pixel
in the
Camera Control Window
help
determine the best focus.
