Meade Instruments Corporation
Telescopes · Binoculars · Microscopes


 
Meade LX50 Schmidt-Cassegrain Instruction Manual
 APPENDIX B: MAINTAINING YOUR LX50
IMPORTANT NOTICE! Never use a telescope or spotting scope to look at the Sun! Observing the Sun, even for the shortest fraction of a second, will cause irreversible damage to your eye as well as physical damage to the telescope or spotting scope itself.
[ toc ] 1. Keeping Your Telescope Clean

Prevention is the best recommendation that a telescope owner can follow in keeping astronomical equipment in top working order. Proper measures taken during observations and when storing the equipment between observation sessions can add many years of trouble free use.

Dust and moisture are the two main enemies to your instrument. When observing it is advisable to always use a proper fitting Dew Shield (such as the Meade #710, or #712). The Dew Shield not only prevents dew from forming, and dust from settling on the corrector plate lens, it prevents stray light from reducing image contrast.

Although dew shields go a long way to prevent moisture build-up, there can be times when the telescope optics will have a uniform coating of moist dew. This is not particularly harmful, as long as the instrument is allowed to let the dew evaporate. This can be done with a hair dryer, or just setting up the telescope indoors with the dust covers removed. It is also advisable that you let the foam for the LX50 dry out indoors for a day if the night was moist. Packing your telescope away in moist foam can result in giving it a steam bath later.

Never attempt to wipe down optics that are covered with dew. Dust and dirt may be trapped with the collected dew, and upon wiping the optics you may scratch them. After the dew has evaporated you will most likely find them in fine condition for the next observing session.

If you live in a very moist climate, you may find it necessary to use silica dessicant in a packed telescope to ward off moisture and the possibility of fungus growing on and within the coatings of the optics. Replace the silica dessicant as often as necessary.

Those living in coastal areas or tropic zones should also cover the electronic ports on the Power Panel and the Keypad with gaffers tape to reduce corrosion on the metal contacts. Apply a dab of a water displacement solution (such as WD-40) with a small brush on all of the interior metal contacts and the input cord metal contacts. The Keypad and all separate accessories should be kept in sealable plastic bags with silica dessicant.

A thick layer of dust will attract and absorb moisture on all exposed surfaces. Left unattended, it can cause damaging corrosion. To keep dust at bay when observing, the telescope can be set up on a small section of indoor/outdoor carpet. If you are observing for more than one night in a row, the telescope can be left set up, but covered with a large plastic bag (such as the one supplied with the telescope). The rear cell opening of the LX50 can also be sealed off to the elements by threading on the optional Skylight 1A Dust Seal. Eyepieces, diagonals, and other accessories are best kept in plastic bags and stored in cases, such as the Meade #50 Accessory Case*.

All of the non-optical surfaces of the LX50 should be cleaned routinely with a soft rag and alcohol to prevent corrosion. The cast metal surfaces and the individual exposed screws can also be kept looking new and corrosion free by wiping them down with a water displacement solution (such as WD-40). Take care not to smear the solution onto any optical surface, and to wipe up any excess solution with a clean dry cloth. The painted tube can be polished with a liquid car polish and a soft rag.

Surprisingly, the most common telescope maintenance error is cleaning the optics too often. A little dust on any of the optical surfaces causes virtually zero degradation of optical performance. It should be of no concern whatsoever to see some small particles on the inside or outside of telescope optics. Should the optics get more dust on them than you would care for, simply use a photographic grade camel hair brush with very gentle strokes. You can also blow off dust with an ear syringe (available from a local pharmacy).

There is a point, however, when the optics must be cleaned. This is when you can easily tell that there is a thin layer of fine particulates that make the optics look very slightly hazy. To clean the optics we must suggest that you make your own lens cleaning solutions, since it is impossible to know all of the ingredients used in commercial lens cleaners. Pure isopropyl alcohol (90% or better) will clean most residual film build-up on optical surfaces (and metal surfaces too).

For removing saliva marks, grease, fingerprints, or most any oily residue, the following recipe is advised: 1 part pure isopropyl alcohol, 2 parts distilled water, and 1 drop of biodegradable liquid dishwashing soap per pint of solution. This formula is safe for multi-coated, or even non-coated optical surfaces. Sprayer bottles make for convenient dispensing of the lens cleaning solutions.

It is advised that you avoid many of the so-called lens cleaning papers (many which contain fiberglass), lens cloths, or chamois. Use a white "Kleenex"-type tissue. The tissue can be formed into smooth pillow surfaces. Make several of these before starting the cleaning process. If the optics are small (such as viewfinders or eyepieces), the tissue can be rolled to the appropriate thickness and then broken in half to create two cleaning wands.

Before attempting to clean an optical surface with a liquid solution, it is very important that as much dust as possible is removed by using forced air and/ or gentle strokes with a photographic grade camel hair brush. The forced air can come from a rubber ear syringe, or canned compressed air from a photographic supply store. Be sure to hold the canned air in a vertical position and try spraying compressed air on your hand before aiming at the optics to see if any of the propellant (solid material) comes out. Propellant is very difficult to remove from optics, so take care not to tip the can when using it. If you have access to a compressor hose, be sure that it is filtered to prevent oil from being sprayed on the optics.

Once you are confident that you have removed most of the dust and large particles, begin cleaning with the pure isopropyl. Pour or spray enough solution onto a pillow or wand of tissue until it is quite wet. If you are cleaning a corrector plate, use radial strokes with a smooth pillow of tissue, starting from the center out using no pressure. If you are cleaning small optical surfaces, use the rolled wands of tissue starting from the edges then spiraling in to the center, again using no pressure. Never pour or spray the solution onto the corrector plate or eyepieces themselves, as the liquid may go behind or in between lenses, where it is difficult or impossible to reach. Never attempt to disassemble an eyepiece to clean the inner elements, as you will certainly not be able to properly center and re-assemble the optical train.

Use dry tissue to make the final clean up, again using no pressure. If there is still some sort of residue, use the the three part formula described above, again using the same cleaning techniques.

The inside surface of the corrector plate and secondary mirror may at some point become dirty due to particles falling inside the tube when removing or replacing the rear dust cover or threading on accessories. To reduce the chance of interior contamination, the Meade Skylight 1A Dust Seal is very effective. If the Dust Seal is not used, it helps to have the rear cell pointed downward when replacing the rear dust cover or attaching accessories.

Another more serious, but not damaging problem is the possibility of a hazy (usually uneven) film building up on the inside of the corrector plate. This can be caused by environmental pollutants, or temperature changes reacting with the interior paint, causing outgassing or water condensation, or combinations thereof.

It is possible to clean the interior of the optical system yourself or to have it done professionally. In the case of the former, take great care in handling the optics. Any impact or rough handling can damage the surfaces, which may require complete optical replacement at Meade Instruments at substantial cost. Meade Instruments assumes no liability for damage incurred to the telescope by the customer.

The cleaning techniques described above are used while cleaning the interior of the optical system, with one exception: Do not apply cleaning solutions to the front surface mirrored optics. Only use the soft camel hair brush and the suggested ear syringe for removing particles. The corrector plate can be cleaned in the normal manner. To remove the corrector plate, follow the instructions below:

1. Remove the six (for 7" and 8" models) or the eight (for 10" models) stainless steel screws that hold the plastic corrector plate retaining ring with the raised white lettering in place. This should be done with the Drive Base placed flat on a work bench, and the optical tube assembly pointed up at a 45 degree angle with the declination lock secure to prevent accidental dislodging of the corrector plate.

2. Remove the plastic retaining ring and locate the two white alignment marks, one at the edge of the corrector plate lens and one beside it on the black metal front cell. These two marks line up and serve as the precise rotational position of the corrector plate in the optical train. If no marks exist, make two yourself with a small paintbrush and some white paint, so that when you return the corrector plate to the front cell you are putting back on the same way that you took it off.

3. Remove the corrector plate from the telescope, holding it by the plastic central secondary housing. Flip it over so that the secondary mirror is facing you, then reinsert the corrector plate back into the front cell. This will allow you full access to clean the interior optical surfaces without touching them with your fingers.

4. When cleaning is complete, replace the corrector plate in its original position, carefully lining up the rotational index marks. Then replace the plastic retainer. Partially thread in all of the stainless steel screws, then one at a time snug the screws down to prevent the corrector plate from rotating in the front cell. Take care not to overtighten the screws as it will stress the corrector plate lens.

5. A final check of the optical system is to inspect for proper collimation (alignment) of the optics.

[ toc ] 2. Collimation (Alignment) of the Optical System

The optical collimation of any astronomical telescope used for serious purposes is important, but in cases of the Schmidt-Cassegrain design of the 8", and 10" LX50 , such collimation is absolutely essential for good performance. Take special care to read and understand this section well so that your LX50 will give you the best optical performance. Note: The 7" Maksutov-Cassegrain LX50 does not require collimation.

For final optical tests, every Meade Schmidt-Cassegrain is precisely collimated at the factory before shipment. Our company is well aware that through shipment and normal handling, the optical alignment can be lost. The design of the optical support system make the method of collimation easy to do. Even the uninitiated can make an alignment of the optics to the same high precision that is performed in the Meade Instruments Optical Laboratories.

To check the collimation of your LX50, center a bright star that is overhead, with the supplied 26mm eyepiece. To make a correct evaluation of the alignment it helps if the telescope has been allowed to either cool down or warm up to the temperature where the instrument is set up. Temperature differences between the optics and the outside air can cause distortion in the images.

With the star or hot spot centered, de-focus the image. You will notice that the out of focus star image looks like a ring of light (the dark center of the ring is the shadow of the secondary mirror). Turn the focus knob until the ring of light fills about 1/8th of the eyepiece field. Take note that if you keep de-focusing the star past about 1/8th of a field, that the ring will look perfectly concentric (even on all sides) even if the optics are out of alignment, preventing you from seeing any misalignments. If the ring of light does not seem to be even on all sides, or if the dark center seems to be offset in the in the ring of light, follow the method below:

1. To make collimation easy, the only adjustments possible on the 8" or 10" LX50 come from the three set screws (shown in Fig. 26) located at the edge of the outer surface of the secondary mirror housing.

DON'T FORCE THE 3 COLLIMATION SCREWS PAST THEIR NORMAL TRAVEL AND DO NOT LOOSEN THEM MORE THAN 2 FULL TURNS (COUNTERCLOCKWISE DIRECTION), OR THE SECONDARY MIRROR MAY COME LOOSE FROM ITS SUPPORT. YOU WILL FIND THAT THE ADJUSTMENTS ARE VERY SENSITIVE: USUALLY, ONLY TURNING A COLLIMATION SCREW 1/2 A TURN WILL GIVE DRAMATIC RESULTS.

Figure 27: Defocused Star Images

2. While looking at the de-focused star image and noticing which direction the darker shadow is offset in the ring of light or noticing which part of the ring is the thinnest (1, Fig. 27), place your index finger in front of the telescope so that it touches one of the collimation set screws. You will see the shadow of your finger in the ring of light. Move your finger (or an assistant's finger) around the edge of the black plastic secondary mirror support until you see the shadow of the finger crossing the thinnest part of the ring of light. At this point, look at the front of the telescope where your (or your assistant's) finger is aiming. It will either be pointing directly at a set screw, or it will be between two set screws aiming at the set screw on the far side of the black plastic secondary mirror support. This is the set screw that you will adjust.

3. Using the telescope's slow motion controls, move the de-focused image to the edge of the eyepiece field of view (2, Fig. 27), in the same direction as the darker shadow is offset in the ring of light.

4. Turn the set screw that you found with the pointing exercise while looking in the eyepiece. You will notice that the star image will move across the field. If while turning the out-of-focus star image flies out of the eyepiece field, then you are turning the screw the wrong way. Turn the opposite direction and bring the image to the center of the field.

5. If while turning, you feel the screw get very loose, tighten the other two screws by even amounts. If while turning the set screw gets too tight, unthread the other two by even amounts.

6. When you bring the image to center (3, Fig. 27), carefully examine the evenness of the ring of light (concentricity). If you find that the dark center is still off in the same direction, continue to make the adjustment in the original turning direction. If it is now off in the opposite direction, you have turned too far and you need to turn in the opposite direction. Always double check the image in the center of the field of the eyepiece.

7. You may find after your initial adjustment that the dark center is off in a new direction (e.g. instead of side to side off, it is off in an up and down direction). If this is the case follow steps 2 through 6 as described above to find the new adjustment screw.

8. Now try a higher power (e.g., 9mm or less) eyepiece and repeat the above tests. Any lack of collimation at this point will require only very slight adjustments of the 3 set screws. You now have a good collimation.

9. As a final check on alignment, examine the star image in-focus with the higher power eyepiece as suggested above, under good seeing conditions (e.g., steady atmospheric conditions). The star point should appear as a small central dot (the so-called "Airy disc") with a diffraction ring surrounding it. To give a final precision collimation, make extremely slight adjustments of the 3 set screws, if necessary, to center the Airy disc in the diffraction ring. You now have the best alignment of the optics possible with this final step.

[ toc ] 3. Adjusting the Right Ascension Lock

After a period of time, it is possible that the R.A. lock (7, Fig. 17) of the LX50 will not tighten sufficiently due to internal wear of the clutch mechanism. In such an event, remove the R.A. lock lever using one of the hex wrenches supplied with the telescope. Then, with a pair of pliers, tighten the shaft protruding outward from the drive base until you cannot easily rotate the fork arm in R.A. (Take care in this operation not to damage the cosmetic finish of your LX50). Replace the R.A. lock lever so that its handle points straight out from the cross-bar connecting the fork arm.

[ toc ] 4. Behind the Power Panel

The 1 amp slow blow fuse will sacrifice itself to protect the LX50 electronics in the event of a current overload. The illustration below shows the location of the fuse.

Figure 28: Reverse Side of Power Panel

[ toc ] 5. Factory Servicing and Repairs

Meade LX50 7", 8", and 10" models have been designed and manufactured for years of trouble-free operation and repairs should rarely be necessary. If a problem does occur, first write or call our Customer Service Department. Do not return the telescope until you have communicated with us in this way, since the great majority of the problems can be handled without the return of the telescope to us. However, should the occasion arise that the instrument requires factory servicing, a Meade Instruments Customer Service Representative will issue a Return Goods Authorization (RGA) number and give you full instructions on how to use it. Product returned without the RGA may greatly delay any servicing or repairs. When telephoning or writing, please explain the exact nature of the problem so that we may offer a prompt remedial procedure. Be sure to include your full name, address, phone and fax numbers where you can be reached.

Should you live outside of the United States, contact your Authorized Meade Distributor from whom you purchased the instrument.

You can reach the Meade Instruments Customer Service Department either by mail, phone, or fax at: Meade Instruments Corporation, 6001 Oak Canyon, Irvine, CA 92626-4205, telephone (949) 451-1450, or telefax (949) 451-1460. Outside of the U.S.A., dial your International Access Code, then 1, then the ten digit number above in the 949 area code.

Table 3: Specifications and Features

Feature 7" LX50 8" and 10" LX50's
Optical Design Maksutov-Cassegrain Schmidt-Cassegrain
Clear Aperture 178mm (7") 203mm (8"); 254mm (10")
Primary Mirror Diameter 209.6mm (8.25") 209.6mm (8.25"); 263.5mm (10.38")
Focal Length 2670mm 2000mm (8"); 2500mm (10")
Focal Ratio (Photographic Speed) f/15 f/10
Near Focus (approx.) 50 ft. 25 ft. (8"); 50 ft. (10")
Resolving Power (arc secs.) 0.64 0.56 (8"); 0.45 (10")
Super Multi-Coatings (EMC) Standard Standard
Limiting Visual Magnitude (approx.) 13.5 14.0 (8"); 14.5 (10")
Limiting Photographic Magnitude (approx.) 16.0 16.5 (8"); 17.0 (10")
Image Scale (degs./inch) 0.54 0.72 (8"); 0.57 (10")
Maximum Practical Visual Power 450X 500X (8"); 625X (10")
35mm Angular Film Coverage 0.52° x 0.74° 0.68° x 0.97° (8")
0.54° x 078° (10")
Optical Tube Dimensions (dia. x length) 9.1" x 19.0" 9.1" x 16" (8"); 11.75" x 22" (10")
Secondary Mirror Obstruction (dia.; %) 1.9"-7.4% 3.0"-14.1% (8")
3.7"-13.7% (10")
Telescope Mounting Heavy-duty fork-type; double tine Heavy-duty fork-type; double tine
Setting Circle Diameters Dec: 6"; RA: 8.75" Dec: 6"; RA: 8.75"
RA Motor Drive System 4-speed, microprocessor - controlled 9v. DC servo motor, 5.75" LX worm gear 4-speed, microprocessor - controlled 9v. DC servo motor, 5.75" LX worm gear
Hemispheres of Operation North and South, switchable North and South, switchable
Declination Control System 4-speed, microprocessor - controlled 9v. DC servo motor, tangent arm 4-speed, microprocessor - controlled 9v. DC servo motor, tangent arm
Slow-Motion Controls Manual and electric, RA and Dec Manual and electric, RA and Dec
Bearings Dec: Nylon; RA: 1 - 4" dia. And 1 - 2.25" dia. ball bearings Dec: Nylon; RA: 1 - 4" dia. And 1 - 2.25" dia. ball bearings
Hand Controller PIC16C54 microcontroller, 5 - button keypad; red LED speed - rate indicator PIC16C54 microcontroller, 5 - button keypad; red LED speed - rate indicator
Main Controller PIC16C57 microcontroller PIC16C57 microcontroller
Onboard Celestial Object Database N/A N/A
Slew Speeds RA and Dec: 2x, 8x, 16x, 32x sidereal RA and Dec: 2x, 8x, 16x, 32x sidereal
Materials: Tube body Aluminum Aluminum
   Mount Castings Aluminum Aluminum
   Primary & Secondary Mirrors [Note 1] Pyrex® glass Pyrex® glass
   Correcting Plate/Lens BK7 optical glass Clear float glass
Telescope Dimensions, Swung Down 9.25" x 15" x 33" 9.25" x 16" x 25" (8")
12" x 19" x 31" (10")
Shipping Carton Dimensions 38" x 22" x 14" 31" x 22" x 14" (8")
38" x 26" x 18" (10")
Total Net Telescope Weight 82 lbs. 71 lbs. (8"); 89 lbs. (10")
Heaviest Sub-Section for Field Assembly 49 lbs. 38 lbs. (8"); 55 lbs. (10")
Total Shipping Weight (approx.) 106 lbs. 91 lbs. (8"); 122 lbs. (10")
#1220 Field De-rotater N/A N/A
Equatorial Wedge Latitude Range [Note 2] 23° to 64° 23° to 64° (8")
15° to 64° (10")
Field Tripod Height [Note 2] 30" to 44" variable 30" to 44" variable
[1] All Pyrex glass used in Meade Schmidt-Cassegrains and Maksutov-Cassegralns is of Grade-A quality, fine-annealed.
[2] The standard equatorial wedge adds approx. 9", and the Superwedge approx. 12", to the stated tripod heights.

Related Topics:


| home | about meade | product information | dealer locator | Meade 4M |
| customer support | investor relations | dealer support |
| employment opportunities | site map |

® The name Meade, the Meade logo, and ETX are trademarks registered with the United States Patent Office,
and in principal countries throughout the world.
Copyright © 2006 Meade Instruments Corporation, All Rights Reserved.
This material may not be reproduced in any form without permission.