The Nexstar 8 is an excellent visual scope that offers the classic Celestron 8" F/10 Schmidt Cassegrain telescope (SCT) optical tube on an easy-to-use alt-az computerized goto mount. Mine is modified with a clever device called "Ray's Brackets" which allow the optical tube to be easily re-balanced or removed. Unfortunately the Nexstar 8 is not well suited for long-exposure imaging. An equatorial wedge is available, but even with the wedge the precise polar alignment needed for imaging proved to be elusive. The tracking of the R.A. drive is problematic for long exposures and drive backlash makes precise guiding difficult. But for short exposure planetary, lunar or solar imaging the Nexstar 8 works fine.
The C8 OTA is essentially the same classic Celestron 8" F/10 SCT optical tube as used on the Nexstar 8. Unlike the Nexstar 8 OTA, the C8 OTA supports the Fastar imaging system. Fastar is a system where the secondary mirror of the SCT is removed and replaced with special lens assembly. A CCD imaging camera like the ST-237 is attached to the Fastar lens assembly. The result is a F/1.9 Schmidt camera with a field of view of 32 arc-min x 42 arc-min.
The Sky90 is a 90 mm Fluorite doublet apochromatic refractor. It has a 500 mm focal length for a fast focal ratio of F/5.6. The Sky90 can be combined with a specialized 1.6x barlow-lens called the Extender-Q which results in a focal length of 800 mm and a focal ratio of F/9.
Sky90 on EM-10 with Extender-Q and ST-7E camera
Note: A Losmany-style dovetail system is used to balance scope with various
heavy rear loads. Dovetail system consists of Astro Physics EM-10 adapter, Astro
Physics DOVELM dovetail saddle, Losmandy DUP dovetail plate and Parallax tube
rings.
The Vixen Great Polaris DX is a german equatorial mount made by Vixen in Japan and imported by Orion Telescopes. The SkySensor 2000 PC is a computer controller and a pair of motors which drive the mount. The SkySensor 2000 PC provides goto functions and can control the mount directly or it can be connected to a PC via a RS-232C serial port. The PC can then control the mount using planetarium software like Software Bisque's TheSky.
I wrote a driver to allow TheSky to control the Temma PC Jr EM-10. It is available
here.
Now that I have a driver for TheSky I think this mount is just wonderful for
imaging with lightweight loads (up to about 20-25 lbs).
Takahashi EM-10 Temma PC Review
The Casio QV-8000 is a general purpose
digital camera. It takes images with a maximum resolution of 1280 x 960 pixels.
There are several features of the Casio cameras that make them well suited for
certain kinds of astrophotography. One feature is that they will take exposures
of up to 64 seconds. Second is that the Casio camera will automatically take
and subtract a dark frame when any exposure over 1 second is taken. (A dark
frame is an exposure of the same duration as the normal or light exposure but
for the dark frame the shutter remains closed. This dark frame records the thermal
noise of the CCD chip. the dark frame is then subtracted from the light frame
resulting in a better signal to noise ratio for the final image.) Third the
QV-8000 has an 8x optical zoom lens that makes it easier to get good results
with some subjects like planets.
The QV-8000 is a fixed-lens
camera so it is used afocally with a telescope. This means that the camera is
attached such that it is photographing the image through a telescope eyepiece
in the same way that your eye looks through the eyepiece. The QV-8000 has a
M43x0.75 filter thread. I use a stepup ring to convert between the filter thread
and a T-thread (M42x0.75). The camera threads onto an eyepiece projection adapter
from Scopetronix. The eyepiece projection adapter holds an eyepiece usually
a 25 mm Plossl.
In order to focus the telescope I use a second eyepiece projection adapter with
a second similar eyepiece that has been adjusted to be parfocal with the camera.
I then substitute the camera and eyepiece adapter. The camera is set to focus
at infinity.
SBIG ST-237
Software Bisque CCDSoft v5
Cyanogen MaximDL/CCD v2.11
Software Bisque TheSky v5 Level 4
Kagayaki III Navigation Edition
Content updated Feb. 20, 2002