SkyDude
Astronomy
EQUIPMENT
Astro-Tech
AT8RC 8" Ritchey-Chretien
Likes:
- Great
bang for the buck!
- True
Ritchey-Chretien, with no coma
or chromatic aberration.
- Capable
of superb images with well-shaped
stars across the entire image.
- Plenty
of back focus accommodates just about any imaging setup.
- Comes
with dual-speed focuser.
- Open
front eliminates dew problems.
Dislikes:
- Field
flattener required, as with all Ritchey-Chretiens.
- Flexure
in the primary mirror cell necessitates use of OAG.
- Collimation
instructions in manual are not good for imaging.
- Focuser
is adequate, but somewhat erratic.
All Ritchey-Chretiens
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
image. Fortunately
this problem is magically fixed by using a proven field
flattener
such as the Astro-Tech ATFF2 or the Astro-Physics CCDT67.
The
focuser attaches to the read mirror cell, not the back of the
tube, so
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
be
considered mandatory for good imaging results.
Improper collimation
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.
Collimation is
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
Likes:
- 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
chromatic aberration.
- Light enough to
double as a guide-scope.
Dislikes:
- Not a true apochromatic triplet.
Celestron
CI-700 Mount
This
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
imaging.
Likes:
- Low Periodic Error (typically
10-15 arc-sec)
- Very Sturdy
- Smooth Drive Corrections (easy
to guide)
- Manual Slow-motion Controls
Dislikes:
- Slow Slew Speeds
- Polar-finder is small and
non-illuminated
- 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
Likes:
- Along with the
QYH8, perhaps the best bang-for-the-buck for a used CCD
one-shot-color camera.
- Real Astro-CCD features:
Thermal-electric cooling (TEC) and 16-bit A/D.
- Large pixels results in very
good sensitivity.
- IR-cut filter is not
aggressive (allows plenty of red).
- Low current draw - 1 amp.
- Proven reliability.
Dislikes:
- 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
seconds.
Someday
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.
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
signal/noise ratio
that allows more accurate calculation of the star
position. Highly
recommended!
Likes:
- 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.
Dislikes:
- 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.
Likes:
- Sturdy, well designed unit.
- 100 degrees rotation without
detaching from camera.
- Adjustable tilt pick-off
mirror.
- Threaded top of turret rotates
for guide camera focus.
- Comes with plenty
of T-thread spacers and 2" front adapter.
Dislikes:
- Not a "thin" OAG, adds 30mm to
back focus requirement.
Past
Equipment
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
a Ritchey-Chretien.
ADM Side-by-side Platform:
For
a few years I mounted the Meade SCT and the ED80 on a
side-by-side
platform which allowed imaging or
guiding through either scope. It's a convenient setup, being
able
to switch between wide-angle or higher magnification
imaging
at will. But flexure problems with the new AT8RC forced me to change to
an off-axis-guider.
Before that, the ED80
was
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.
Philips ToUCam
Pro 740 Webcam:
Although
usable as a guide camera through a guide-scope, it just doesn't have
the sensitivity to guide well on anything other than very
bright
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
looked backed.
Nikon
D50 DSLR
The
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
remote
"clicker". Canons or later model Nikons don't have these problems.
Nikon Infra-red Filter:
All
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.
Meade 8"
LX50 SCT
My
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
amount of
film-based imaging. Later, I mounted the OTA (optical tube
assembly) to a Celestron
CI700 mount for better and easier guiding.
Jason Schmidt-Newtonian
My
1st scope was an inexpensive one from a department-store, complete with
wobbly tripod.
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
the eyepiece!)
Comments
welcome: mark.eby@twc.com