LX10 Fixes
Contrary to conventional belief, the LX10 has a pretty good drive
system
and mount that is more than good enough for astrophotography (consider
the fact that for decades photographs were taken with early Meade and
Celestron
SCTs that had drives significantly inferior to the LX10's). There
are a few simple improvements that can be made, however, that can
improve
the scope considerably.
Note: I recently was lucky enough to be one of two main
developers
of a new small local public observatory. (See http://indianastars.us).
One of the scopes we have there is a 12" LX200, so now I've had a good
chance to compare the LX10 with the LX200. Mechanically, I
haven't
noticed a significant difference in stability, accuracy, etc.
Mostly
the LX200 has some computerized features (mainly periodic error
correction
and backlash compensation) and quartz regulated drive rates that
improve
the accuracy of the drive system. But the LX10 is still more than
good enough for photography. I took passable pictures with my
first
"serious" scope, an original classic Celestron C8, over 20 years
ago.
By comparison, the LX10 has hundreds of dollars worth of improvements
over
that scope (e.g., worm drive vs. spur gear, built in RA drive
corrector,
etc.) for essentially the same price I paid 20 years ago (price not
corrected for inflation!).
See also my page on how
to connect an autoguider to an LX10, with samples of my LX10
astrophotography.
Questions or comments? Email me at jmmahony@hotmail.com.
Tripod
The tripod normally sold with the LX10 is uncomfortably short if you
want
to use it from a standing position (it looks a bit weak too, but
I haven't had that much experience with it). Fortunately the
tripod
is sold separately so you can just get the standard adjustable tripod
(normally
used with the LX200) instead for a little extra money. For a
cheaper
and lighter solution, see if you can find one of the old "locked
triangle"
tripods that were made for the original classic Celestron C8.
These
were remarkably rigid and very light. The only drawback is that
for
storage, the legs fold up (over the head) rather than down, which makes
them a bit awkward to set up until you get used to it.
Fortunately,
the light weight makes that considerably easier than it sounds.
The
central hole in the head is only 1/4" rather than 1/2", so you'll need
a 1/4" bolt and a bushing (spacer) for the hole in the Meade wedge.
Wedge
This works pretty well. I replaced the tilt plate clamping/coarse
adjustment bolts with hand-knobs (see http://www.scopestuff.com)
since the tilt has to be adjusted slightly each time it is set up,
unless
you regularly set up on a level paved surface (which should be
avoided-heat
from a paved surface will cause image-degrading turbulance in the air,
and vibration-dampening is better on a dirt surface). I couldn't
find a hand-knob with a long enough shaft to replace the adjusting
screw,
so I just used a length of 1/4" threaded rod with the end bent over to
make a handle, which has worked very well.
RA Drive
The LX10 has a good worm drive with about 1 arcminute periodic error
(similar
to the LX200, before applying the LX200's periodic error
correction).
My only complaint is that it uses a simple DC motor with a
voltage-regulated
power source. Quartz regulated systems are cheap today so that
would
have been better. The system is stable enough for the time period
required
for a single exposures, but from night to night, as temperature
variations
and battery power affect the drive rate, you'll want to know about the
variable resistor (accessible through a panel on the bottom of the
drive
base) that can be tweaked to affect the drive rate. Since this
control
is hard to get to, you may want to remount it somewhere on the front of
the scope. See also this part
of my Autoguided LX10 page for info on replacing this 500 ohm
variable
resistor with a 200 ohm variable and 300 ohm fixed resistors for better
control.
Declination
In a recent review of several small telescopes, Sky&Telescope
commented
on how frequently simple, easily avoidable design errors show up in
telescopes.
Meade has a reputation for good optics, and their computer systems
generally
seem better thought out than Celestron's, but their weak point is
mechanical
design. On the LX10, this shows up in the small threaded part at
the end of the tangent arm (see picture). The arm itself seems to
be made out of a special, extra-stiff, aluminum alloy, but after going
through that extra trouble, the simple threaded part that the dec
fine-adjustment
screw goes through has multiple problems. First, it could have
been
made almost twice its diameter (for less play between it and the arm)
without
limiting the range of motion of the arm. But even worse, it is
only
threaded for about half of its diameter (the rest is bored out to a
larger,
non-threaded size). This leaves only about 1/4" of threaded hole,
which means the fit between it and the dec adjustment screw is sloppy,
causing some backlash. If you have access to a metal lathe, I
would
suggest making your own replacement part, but if not, a simple fix is
to
drill and thread a small hole perpendicular to the dec adjustment
screw-hole
in this part and put a small nylon thumb screw in it, so that this
screw
presses sideways against the dec adjustment screw. That presses
the
dec screw against the threads to remove the play. Using a
thumbscrew
allows this to be loosened for visual use, so that the dec screw turns
easier for easier manual dec adjustment.
Note the narrow inch long black screw parallel to the dec adjustment
screw and above it, on the tangent arm. This screw was loose in
the
box when I got my scope, and I only recently (after seeing someone
else's
LX10) found out what it's for. As you can see in the picture, the
tangent
arm is split at the end and the screw can be tightened for a better fit
between the split end of the tangent arm and the small part that forms
the connection between the dec adjustment screw and the tangent
arm.
I haven't experimented with this yet.
Dec Motor
For deep-sky photography, you'll need the dec motor (sold
separately).
Mine works well, with insignificant backlash. The only part I had
a problem with was the clutch. The motor tucks under the fork
arm,
and has a small gear on the shaft. You take off the rear dec
fine-adjust
knob and replace it with a plastic hub that has a larger gear on it
that
meshes with the motor gear. Like most such dec motor assemblies,
there is an adjustable clutch that allows you to use the dec knob
either
manually, or via the motor, or both. The clutch can be adjusted
tight,
for motorized control during photographic guiding, or loose, for manual
control during visual use, or partially tightened for both. The
problem
in this case is the way the clutch adjustment works. The large
gear
goes over the hub on the end of the dec screw, with a slightly loose
fit.
There is a plastic cap over the end of the hub that presses the gear
against
a rim on the hub, for clutch action. The cap has a small hole in
it that fits over a tiny 1/2" long #4-40 threaded stud that is threaded
and glued into the end of the hub. A nylon-insert type locknut is
threaded onto the end of the stud. If you tighten the nut, it
presses
the cap against the gear, which gets squeezed between the cap and the
rim
on the hub to increase the friction. There are two problems with
this: first, if you have it adjusted partly tight for both manual
and motorized use and turn the front dec knob, the clutch-cap tends to
rotate against the locknut and tries to turn it. This is why
Meade
uses a locknut, but the torque on the stud can end up breaking the glue
loose and loosening the stud. Second, the dec knob is a rather
"fine"
control, so it has to be turned a lot at medium or low power to make a
difference. The dec screw has a lot of friction when the clutch
is
"partly" tight, so using this setting will wear your fingers out
quickly.
Thus you'll be adjusting the clutch a lot to go from loose (fully
manual)
to tight (motor control). If you use a small wrench on the nut,
you'll
risk breaking the glue on the stud, so the end of the stud has a small
hex hole in it that you're supposed to put a tiny allen (hex) wrench in
to keep the stud from rotating. But with small parts, and with
very
little slop in the motor, it's difficult to keep the tiny hex wrench in
a fixed enough position. Further, using these small tools is a
pain
in general, especially when you're working in the dark. I
eventually
broke the glue (I think I forgot to use the hex wrench at least
once).
Rather than trying to reglue it, I used a small 4-40 screw that I
threaded
through a nylon wing nut first (with the "wings" toward the head end of
the bolt) and left out the locknut. The wingnut takes the place
of
the locknut, and is very easily switched from tight to loose.
When
it's in the fully tightened position for motorized guiding, it's tight
enough to not come loose (no glue or locknut needed). It's very
easy
to loosen for manual use, and I haven't had any trouble with the 4-40
screw
loosening.
In my case the stud had already come loose, so I figured using a normal
screw with a head would prevent the wingnut from ever fully unscrewing
and falling off and getting lost, but I've since heard from others who
left the original headless stud in and just put the wingnut on that
(minus
the original locknut, of course). They haven't had any problem
with
the wingnut coming off.
Finderscope
In a letter to the editor of Sky& Telescope, (in reference to the
above
mentioned article) a reader pointed out a manufacturing error in the
6X30
finderscope that Meade (and Celestron) uses. I discovered this
error
by accident: the field lens of the finder's eyepiece is installed
backwards. The manufacturer (some generic scope accessory maker,
not Meade itself) has apparently been doing this for years. The
finder
has a focusing adjustment, but the reversed lens affects the adjustment
range and may also (depending on your eyesight) make the crosshairs out
of focus. Fixing this is easy: unscrew the eyepiece end and
take out the plastic press-fitted retaining ring. Be careful!-the
rest of the parts slide out of the eyepiece tube easily then!
Make
sure you keep everything in the proper order and orientation.
Also
be careful of the crosshairs: they're made of extremely thin wires and
can be easily damaged. I don't recall the exact order of the
parts,
but the eyepiece has two lenses, and the field lens is the one further
from the eye (so it will be the first one you get to as you take out
parts).
Simply reverse the field lens and then reassemble everything.
Battery Pack
I suspect Meade realized too late that the 9V battery doesn't last too
long. They seem to have put in the AA(X4) battery pack as an
afterthought,
and you have to remove the bottom panel to get to it, which is a pain
(no,
it doesn't fit into the 9V battery compartment, at least not on
mine).
There's an easy fix for that: if you read my Autoguided
LX10 page, you know that the external power jack can actually use
any
voltage level down to 6V (it's wired identically to both the 9V and AA
battery sources-the first stage of the voltage regulator reduces any of
these to a common lower level that the rest of the drive circuitry
uses),
so all you need to do is remove the plug on the battery pack and put on
a plug that fits the external power jack (5.5 mm O.D., 2.5 mm I.D.,
readily
available at Radio Shack. The center pin is positive.) Now
you can just plug the batteries in to the external jack, and leave the
batteries sitting on the base plate of the wedge, or maybe find some
way
to attach the battery holder in a covenient place on the drive base.
Back to John's
LX10 Page