Most modifications and 'fixes' that I see on the Internet are primarily for 10" and larger scopes. I felt that there was a gap for the 8" that could be filled, so here we are. The Meade 8" Lx200 is a respectable instrument capable of great images with film or a CCD camera. With a few simple and inexpensive modifications, it can be even better!
(Catch his web site at easyweb.easynet.co.uk/~chrish/Lx200.htm)
Cool-down time for Lx200's can be significantly longer than other telescope designs because of the closed tube. This modification is a step toward improving that problem. A small computer CPU fan or case fan powered from battery (they are very low current draw) will push air through the OTA tube from the back (directly behind and flowing around the primary) letting the tube 'breathe'. This removes the stagnant air, replacing it with cooler ambient air, helping the tube and mirror cool faster.
A close-up of the mounting and airflow holes in the rear cell. The fan was selected for size (bigger scopes have more room for bigger fans) and then drawn out on the OTA as a template for cutting. Drill bits were used for the rough work after the corrector plate and primary mirror were removed for safety and to facilitate cleanup of all the aluminum shavings (see the 'You didn't really take out your primary, did you? section for details on the process of gutting your Lx200).
A Dremel tool finished out the slots nicely after drilling. Only the bare minimum of material was taken out based on the template of the fan's structure. 6x32 mounting holes were then tapped into the aluminum (a bit over 1/8" thick at this point) and short machine screws used to mount the fan.
The small 12v computer fan mounted to the rear of the Lx200. Airflow is small, but direct. Exhaust comes out the eyepiece hole (I must remember to remove the filter!). Fan is powered via 12v battery and the cord is set up with spade connectors for quick disconnect (leaving only a 3" wire attached to the fan). The fan cuts cool-down time to less than half of what it was (about 1/2 hour now).
The Telrad is a great invention, but my quest to eliminate some of the loose battery-powered equipment I had laying around led me to take it apart (never leave well-enough alone). I soldered connections to the internal battery pack and ran a cable out the rear of the unit. It terminates in a 1/8" mono plug that fits the reticule port on the face of the Lx200.
The Telrad was 3v and I didn't figure it would be hurt too much by the Lx200's 5v reticule port. Now I have 2 on/off's (Telrad and keypad) plus I can utilize either brightness adjustment. The other benefit of course is the lack of batteries needed. As long as the scope has power, so does the Telrad.
Telrad modification update: 11/1/00
After using the Telrad as shown above for a while, I have found a few problems with the design. Below is what I found, and how I fixed it..
First, the cord was originally routed through the back of the unit to shorten the wiring path, but this causes a complication in that the 3 collimation screws at the rear of the unit are very difficult to get to! Also, the knot of cord just inside the housing interfered with full motion of the mirror during collimation of the Telrad.
Second, because of the (small) difference in the voltages from the Lx200 control panel compared to the internal battery pack, I needed to remove the batteries when using the cord to avoid 'recharging' my alkaline batteries!
To fix the first problem, I simply rerouted the power cord through the side of the unit where there is plenty of space (and where it should have gone the first time). Another option would be to run out the front of the unit. I also added a 90 degree angled plug to the Lx200 end to avoid the tall plug sticking up there and possible interfering with the lower edge of the fork arm.
For problem #2, I used a low-profile slider switch (to avoid clearance problems on the outside and for the light-path inside) to connect both the battery and external power. 'L' is for Lx200, 'B' is for battery.
The image below shows the internal routing along both sides of the target projector.
The friction of the cast wedge base plate on the tripod head made small azimuth adjustments very difficult with the little knobs supplied with the standard wedge. Pictured here is a circle of 1/8" thick Teflon on the tripod head where it will be sandwiched between the tripod and wedge. Four holes were cut where the mounting bolts come through. The Teflon forms a very smooth surface for the wedge to rotate on and tiny adjustments are now a breeze, even with the large center tripod spreader knob securely tightened.
Much of the 'wandering' pole-star problems I encountered tracked back to the junction of the wedge and the tripod head. The 3 slotted adjustment holes in the wedge base plate are oversized and allow a lot of slop when the fine azimuth adjustment screws are used. The wedge never really pivots around a center point. It slides sideways as it rotates, and it never moves the same way twice. The supplied hex head bolts were also always a pain to work with.
The socket-head bolts supplied to hold the wedge to the tripod head were replaced with large thumbscrews for 'tool-less' operation in the field. They are stabilized in the oversized wedge slots by thin brass tubing (1/64" wall thickness) to get rid of some of the lateral 'slop' in the azimuth adjustment. Each slot was filed out by hand until the tubing would just barely fit, yet still ride smoothly the entire length of the slot. These thumbscrews are large enough to find and adjust, even in the winter when I'm wearing gloves.
Another cause of the excess slop and play when making azimuth adjustments to the wedge was the center hole in the tripod head that allows the bolt to pass from the tripod leg spreader to the knob/compass on the wedge side. The bolt is 1/2" diameter, but the hole in the tripod head that it passes through is 5/8" on the underside and 3/4" on the top, allowing a lot of play and slop.
I removed the retaining clip ( it was the 3rd one anyway, they kept getting mashed and bent inside the hole) and sanded out the hole from the top until a cut down bronze bearing (1/2" ID x 3/4" OD x 1" long) would fit snugly. A light tap to seat it was all that was needed. The hole from the underside had been factory cut almost 1/8" off center and needed to be ground down with a Dremel tool to align the two before the bolt would slide through. The spreader is now removable as there is no place for the clip, but the tight central pivot and lack of play in the wedge are worth the hassle. If the large knob that holds the wedge to the tripod is screwed back on after scope removal when breaking down the setup, the spreader is still held in place nicely.
Friction and play in the Latitude Adjustment
The 'deluxe latitude adjuster' on the standard wedge also bound and walked on the underside of the plate when turned causing inconsistent motion when making adjustments.
The latitude rod and bar were reversed so it would hold on the left side of the wedge plate instead of the right. A block of impregnated nylon was epoxied to the wedge plate on the left side as shown in the picture above. A 1/2" hole was carved into the block with an Xacto knife. I made the mistake of trying to use a drill to make this hole the first time. Let me tell you, even a sharp drill bit has trouble with impregnated nylon- it is super slick!. I then shaped the hole to just fit a ground down brass acorn-nut on the end of the latitude adjuster bolt (shown below).
It forms a deep ball-and-socket joint that has room for the angle to change if I ever move to a different latitude. This setup holds the adjuster steady and straight, and has very little friction. Adjustments are very smooth and fine.
I found that the last little tweaks I put on an alignment when cinching everything down always made the alignment star wander, sometimes completely from the field of view. I tracked this down to extra space between the sides of the wedge and the wedge plate where it swings between them. The was enough room to put a fender washer between the two without binding up the motion. This unfilled space allowed the sides of the wedge to bow together when the side knobs were tightened, deforming the wedge and throwing things out of whack.
Placing washers between the plate and side on just one side (as shown above) took up all the slack and now the sides do not bow or deform when cinched down. It would probably work a little better to use even thinner washers and put them on both sides of the plate.
The 2 upper pivots for the plate itself were held by threaded
knobs and had much play in the hole where they passed through
the side of the wedge. Since the side play when tightening the plate was
fixed (as described above), I really saw no need to have another tightening
point here, and thus another location for slop to present itself.
As shown above, I drilled out (1/4") the threaded portion of the wedge plate mounting holes and put bushings in the wedge sides to get all the holes to 1/4". Then a 1/4" stainless steel rod was pushed through the holes, making an axle for the wedge plate to ride on. There is just enough clearance to allow it to rotate on the rod without binding. The motion is very smooth and has no slop. After this image was taken, the 'axle' was cut to length and capped on both ends to protect clothing, car seat, and my skin!
The curved latitude slots in the sides of the wedge were also a point of loose adjustment so I filed the slots smooth and slightly larger to accommodate bushings over the knobs that hold latitude as well as the bar that holds the latitude adjuster.
In the picture above, one can see the bushings just before the assembly was tightened. The bushings are as long as the thickness of the side, they only protrude here for illustration. Along with the new 'axle' and acorn ball-joint, the motion of latitude is now firm and smooth.
I found that even when doing a careful leveling of the tripod when setting up for the evening, my alignment procedure (polar) was always off a consistent amount when slewing to the second star. The amount varied slightly, but was always on the same side of the Telrad bullseye, about a degree out. I checked the wedge bubble level, and found that it seemed to be a bit off.
To check/solve the problem, I ordered a small precision bubble-level from Edmund Scientifics. It just has 1 circle in the center, and a tiny bubble that fits perfectly within it. Smoothing the surface of the wedge, I super-glued the new level near the old one and set out to realign. As you can see from the picture above, the 2 levels do not show the same reading. I realize this may be due to many reasons besides incorrect calibrations (like paint thickness, level of glue, imperfections in the wedge casting, etc.), but my alignment is about 50% closer now when slewing to that second star. If this saves me even 10 minutes in drift-aligning each time I set up, It was well worth the price of the new level.
Wedge holding-rods design based on Ed Stewart's
'Equatorial Wedge Stabilizer'.
See Ed's 'Astro
Designs' for more details on this and other great ideas and modifications
- 
The rods support the overhanging wedge like pillars holding up a porch or deck. They reach from deep holes in the oak block that is clamped to the leg, to the cast holes on the underside of the wedge. This forms an inverted 'tripod' that holds the overhanging wedge quite securely. Vibration is normally a real problem when using the wedge compared to mounting the scope in Alt-AZ mode. The support rods are tightened by extending the rods upwards via the wing nuts until they take up some of the weight of the wedge. Vibration is reduced significantly (almost back to the Alt-AZ level), dampening out in less than 1 sec. The top of the rods are covered with rubber caps to protect the wedge and help a bit with vibration also.
Wedge Stabilizer update: 11/1/00
After using the stabilizer bars for a time, I found that while they kept vibration down to a minimum, they also prevented easy polar alignment during the azimuth adjustment phase. When adjusting azimuth, the wedge would try to turn in relation to the tripod, but would be prevented by the bars. Easy to fix by loosening one and tightening the other, but that also adjusted the upward pressure on the wedge differently each time and threw off the alignment. The fix was found on another web site I saw a while back (sorry, can't remember where) where an Lx200 owner was using the support shocks from a pickup truck camper-top door in place of the solid rods. His was on a 10" with superwedge so the size needed to be scaled down when converting to my 8" and standard wedge. I just modified my existing rods as shown below.
I shortened the rods to allow room for adding a very stiff spring and a capped copper pipe (3/8" pipe, soldered on end cap) to keep everything together. Assembled and disassembled versions are shown above. In use, they work even better than expected because they also dampen more vibration because of the spring loading. The spring motion also allows one to expand and one to compress while turning the wedge in azimuth during polar alignment. Spring compression allows about 1/2" azimuth movement before binding which is usually more than enough if the scope is set up close to north to begin with.
Shock Rods installed. The red area marks how far I need to compress the units when installing then for a session. It helps in keeping the same pressure on both sides, while keeping me from overtightening also.
Capped ends resting in the molded indents on the bottom of the wedge. They keep themselves pushed into the corners by the spring compression.
More to come !
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Copyright
2003© Anthony J. Kroes.
Last updated 06/13/2003
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