AT8RC 8" Ritchey-Chretien
bang for the buck!
Ritchey-Chretien, with no coma
or chromatic aberration.
of superb images with well-shaped
stars across the entire image.
of back focus accommodates just about any imaging setup.
with dual-speed focuser.
front eliminates dew problems.
suffer from field curvature and astigmatism, which results in
oblong stars at the edge of the image. This is not coma - the stars
are evenly elongated toward and away from the center of the
this problem is magically fixed by using a proven field
such as the Astro-Tech ATFF2 or the Astro-Physics CCDT67.
flattener required, as with all Ritchey-Chretiens.
in the primary mirror cell necessitates use of OAG.
instructions in manual are not good for imaging.
is adequate, but somewhat erratic.
focuser attaches to the read mirror cell, not the back of the
the weight of the camera causes the position of the
primary mirror to flex.
Indeed, there are times when flexure can be
noticed in exposures as short
as 1-2 minutes! Using an off-axis-guider (OAG) solves this and should
considered mandatory for good imaging results.
of the secondary causes stars at one edge to be
more oblong than the opposite
edge, and improper
collimation of the primary results in coma on all stars.
described on another page.
Now that all the kinks
have been worked out, I absolutely love this scope! (Although at one
time I was ready to throw it over a cliff.)
Orion ED80 APO Refractor
- Good, wide-angle performance
for the price.
- No coma, like all refractors.
- Semi-apochromatic with ED
(Extra-low Dispersion) glass results in small amount of
- Light enough to
double as a guide-scope.
- Not a true apochromatic triplet.
is a heavy-duty GEM that used to be produced by Celestron to support
their C-11 and C-14 SCTs from 1999 to 2003. It's basically a cheaper
version of the Losmandy G-11. Although hard to find, some consider it
one of the best bargains in the used mount market. In general I'm very
happy with this mount, and it serves well for both observing and
- Low Periodic Error (typically
- Very Sturdy
- Smooth Drive Corrections (easy
- Manual Slow-motion Controls
- Slow Slew Speeds
- Polar-finder is small and
- Clutches may slip and bind
(can be fixed)
I've modified the CI700 to improve the action of the clutches, and to
allow for quicker and easier set up. See CI700 Mods.
Orion StarShoot Pro V2
- Along with the
QYH8, perhaps the best bang-for-the-buck for a used CCD
- Real Astro-CCD features:
Thermal-electric cooling (TEC) and 16-bit A/D.
- Large pixels results in very
- IR-cut filter is not
aggressive (allows plenty of red).
- Low current draw - 1 amp.
- Proven reliability.
I'll upgrade to a mono-system with all the neat filters, but for now I
have yet to fully utilize this camera to its full potential.
- Large pixels limit resolution
when you zoom-in-and-crop.
- TEC is unregulated and limited
to 30 deg C. below ambient.
- Download is slow, about 10
QHYCCD QHY5-IIM Guide Camera:
I was surprised at how easy it
is to find guide-stars when this camera is used with an OAG. There was also an
immediate improvement in
guiding accuracy, probably due to strong
that allows more accurate calculation of the star
- Very sensitive (QE = 70%),
despite being CMOS, 2X2 bin mode = more sensitivity.
- Video, so it can be
used for lunar/planetary imaging.
- Small size, light weight.
- Low cost compared to other
sensitive guide cameras.
- Long back-focus
of 17mm may present problems when trying to reach focus on an
OAG, but nose-piece can be removed.
Orion Deluxe OAG:
Switching from a guide-scope
to this OAG completely
eliminated the AT8RC flexure problems.
- Sturdy, well designed unit.
- 100 degrees rotation without
detaching from camera.
- Adjustable tilt pick-off
- Threaded top of turret rotates
for guide camera focus.
- Comes with plenty
of T-thread spacers and 2" front adapter.
- Not a "thin" OAG, adds 30mm to
back focus requirement.
Mead 8" SCT OTA
For a few years I
used the OTA from a Meade 8" LX50 SCT for long focal-length imaging.
The optical quality was
good, but not great. There is an expected degree of coma at the edge of
the field-of-view, and the corrector lens in front presents dew
problems. Over time I finally decided to upgrade to
ADM Side-by-side Platform:
a few years I mounted the Meade SCT and the ED80 on a
platform which allowed imaging or
guiding through either scope. It's a convenient setup, being
to switch between wide-angle or higher magnification
at will. But flexure problems with the new AT8RC forced me to change to
Before that, the ED80
mounted on the SCT piggy-back style, but sometimes
there wasn't enough room to get my head in for finding, framing, or
focusing. Switching to a side-by-side platform solved that by allowing
plenty of room.
Pro 740 Webcam:
usable as a guide camera through a guide-scope, it just doesn't have
the sensitivity to guide well on anything other than very
stars. Guiding was sometimes decent, but never great. Don't even think
of using it with an OAG. I upgraded to a QHYCCD QHY5-IIM and never
Nikon D50 is a DSLR (digital single lens reflex) camera that uses one
of the new generation of full-size format, low-noise high-sensitivity
CCD chips. It's similar to the Canon EOS series, except the
D50 cannot be
controlled by computer software such as Backyard EOS. I had to focus
using a par-focal eyepiece, and start/stop exposures using the Nikon
"clicker". Canons or later model Nikons don't have these problems.
Nikon Infra-red Filter:
digital cameras have an IR filter because CCD sensors are overly
sensitive to red light. The result is that emission nebula lacks that
vivid red we love to see, although other objects will image just fine.
Removing the IR filter is difficult, but the links page
may give you ideas on how to remove it.
2nd scope was a Meade 8" LX50. Like most SCTs, it offers a good
compromise between quality and cost. Using the same fork-arms as the
LX200, it may be the sturdiest mount of any mass-produced fork-arm
design. It served well for observing and a limited
film-based imaging. Later, I mounted the OTA (optical tube
assembly) to a Celestron
CI700 mount for better and easier guiding.
1st scope was an inexpensive one from a department-store, complete with
But it presented me those first wonderful sights of the rings of Saturn
and the Orion Nebula., and propelled my interest in astronomy. I even
used it to take photos of the 1991 Solar Eclipse and comet Hale-Bopp.
The camera was mounted on the scope piggy-back, and I used the
slow-motion knobs to
track. (That's right, slowly turning the R/A knob while looking through