Enter “Focus Mode” with the Guide Camera
Make sure your guide camera is attached to the focuser on the Integrated Guider Port and any
required cables are attached. If you have not already done so, connect to the guide camera
with your image acquisition software.
Setup your software in “Focus Mode” to take images continuously. Set the exposure long
enough so that you can see good stars with a high signal to noise ratio in the guide camera
image . In the example below the exposure length is set to 1 second. You may need to adjust
the exposure time in the “Seconds” field up or down in order to capture a few bright stars
without saturating. Setting the exposure time fairly short allows you take more focus images in
a shorter period of time, generally allowing you to achieve sharp focus fairly quickly.
Note:
Critical focus is not as important for the guide camera as it is for your main
imaging camera. Some guiding experts even recommend defocusing the guide
stars just a bit as that produces a smoother distribution of light about the position
of the star. The slightly defocused image can reduce the effects of “seeing”
allowing a more accurate “center of mass” calculation of the guide star resulting in
smoother guiding.
Because the guide camera sees all the light from the stars in the guide camera field of view,
you should be able to find one or more stars suitable for focusing (or guiding) wherever you
happen to be pointing. Refer to Section 1, Field of View, for details on the portion of the sky
viewed by the guide camera relative to the main image sensor.
In MaxIm LE, select View > Camera Control Window, then click the Focus tab. Click “Guider”
to focus the guider. The example below shows binning set to 1. Setting binning to 2 may work
well for focusing the guide camera. Click the checkbox next to “Continuous” to take images
repeatedly with the guide camera. Click “Start Focus”.
Examine the images returned by your image acquisition program. As stars come into focus
they produce a smaller disk of light with more of the total light from the star being focused into
a smaller area. The total size of stars in your guide camera images will vary depending on the
focal length of your telescope, the size of the pixels in your guide camera and your local seeing
conditions.
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