I assembled a collection of widefield images I have taken over the
past few months using Pentax medium format lenses of various focal
lengths (90mm, 150mm and 200mm) with slight variations in the system
configuration. All but one of them were shot using my ST10XME
camera.
The first configuration tried used a separate guide scope and
guide
camera mounted on a Losmandy side by side dovetail plate
arrangement.
I used an AP80/900mm guidescope which is longish and
because of that
there was noticeable differential flexure in that system
that
manifested itself in elongated stars in the corners.
the
next configuration tested was the same setup but with self
guiding used
via the ST10XME camera. So long as the camera is self
guided that is a
potentially workable solution but I found with
Halpha and other emission
line filters that the attenuation of the
guide star was so great that
sometimes guidestar integrations of 15
to 20 seconds was needed.
at a short focal length that is OK except for the time lost in
reacquiring the guidestar after image download and aiming dithering.
It usually takes 4 to 8 cycles of guiding to reacquire good tracking
and that was taking several minutes in some cases. Still I managed to
take
a few nice images with that arrangement, one of which was selected as
an APOD
on Feb 14th of this year.
the third configuration tried was
using a custom made frame that
permits a solid mounting of the
guidescope and will also allow the
imaging camera to be rotated to any
angle from horizontal to
vertical. This gave the functionality I needed
to use a separate
guider without introducing differential flexure and
also let me
optimally frame my object by rotating the camera to an
optimized
angle. One of the first targets taking advantage of this
camera angle
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