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It's a good optic, very versatile and suits
about for all the fields of the observation and the astronomic photography.
In the image above it's mounted inside two strong aluminum rings, and with
a Meade 9x60 finder with illuminated eyepiece and 90° prism, a true
luxury to center the objects.
The principal problem of the optics is
the mirror shift, or the bending of the principal mirror that vary in different
positions in the sky, it causes moved stars in long focus and long exposure
imaging. The solution is to block the mirror, as described in the wonderful
book of Robert Reeves "Wide-Field Astrophotography", page 429. The change
need the insertion of three plastic foils around the mirror at 120°,
that are folded up by three screws so that the foils block the mirror.
The tests on the field have shown that
now the problem is reduced a lot, even if non eliminated. Now it's possible
to realize CCD images of 30 minutes exposure guided with a refractor in
parallel. It needs attention the entity of the blocking strength to apply:
the foils have to gently lean on the mirror, if forced they will distort
the shape causing a worsening in the diffraction figure.
One of the plastic
foils attached inside the tube: in the rest position it does not touch
the mirror.
External view: at
left the screws that block the foil, at right the screw that push the foil
toward the mirror.
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