LX200 RA-axis OTA-axis alignment

My telescope ( LX200 12" ) had a bad pointing accuracy since the first date I bought it.

The most times I had to enable the hi-precision pointing in order to bring the desired object in the 35' eyepiece Field of View.

Making some test I discovered that my OTA-axis and the RA-axis was away of being parallel. 

Knowing that the coincidence of these axis is very important I started to applying some methods I read in the internet in order to improve the pointing accuracy ,  but I had no any success. 

Recently I developed a procedure based in real situations in order to bring the axis in parallel and I am glad to say that the telescope accuracy was significant improved. 

Bellow  I describe this procedure hoping , others LX200 owners with bad pointing accuracy to get help from my experience.

Test It :

 Set up the telescope on the wedge in polar mode . You don't need to connect any power or keypad or the declination cord. Align the viewfinder with the telescope OTA using a reticle eyepiece.

Set the declination setting circles to 90 deg as precise as you can and lock the declination knob. Rotate the OTA in RA in order the declination axis to came parallel to the ground and the viewfinder in the upper position as in fig 1. Set the viewfinder cross-hair x-axis parallel to the declination axis.

1. Using the wedge latitude and azimuth control knobs place the Polaris in the center of the viewfinder FOV as in Fig 2.

2. After that rotate the Ra axis 180 deg so the viewfinder to come in the lower position as in the Fig 3.

3. Examine the new position of the Polaris in the viewfinder field of view related to the finder axis.

Any deviation from the X-axis is not important since apparently you didn't set up precisely the OTA in the 90 deg. You can eliminate it by using the declination slow-motion control in order to place the star half the distance to the X-axis and then using the wedge latitude control knob to the rest till to cross the X-axis Fig 6

4. Repeat the procedure from the point 1 and now examine again the position of the Polaris.

If the star remain to the center of the field you are a lucky owner, the alignment is perfect and you have to search other reason for you bad pointing accuracy.

Any deviation from the Y-axis is due to the OTA-axis and RA-axis misalignment from being parallel. This is the point we are interesting in and we have to improve. 

Fix it :

There are 6 alien screw as in the Fig 7 , 9  (3 in each side ) that  attach the OTA to a plate mounted to the fork arms. The holes housing the screws , are elongated permitting the OTA to slide a while making possible some adjustment.

Now you have to examine which way you need to slide the OTA . A trick I used is to push slight the upper side of the OTA as the arrow in Fig 8 while watching from the viewfinder and examine how the Polaris is moved because of this push. This will guide you how to make the adjustments by examine what set of 3 screws you have to loose and how the OTA need to slide in order to move the Polaris to the center of the field close to the Y-axis.

After you will decide how you plan to move the OTA just loosing the appropriate set of screws bring the OTA in the 0 deg and using the edge of a  screw-driver move the OTA slight  to the direction you have decided Fig 11. Again you have to remember that the star need to move half the distance to the Y-axis

You have to repeat the procedure from the point 1  after each intervention and to learn by your error till to get a satisfied result. If you find the adjustment with the screw not so  effective you can try inserting the appropriate screws in the screwed holes you can see in Fig 10 .Turning these small screws you can push the big alien screw and to slide the OTA to the desired point.

If you have a small amount of misalignment or if you want to have a more accurate adjustment you can use a reticle eyepiece connected with a diagonal to the main OTA instant of using the viewfinder.

Finally don't forget to tighten again the screws in order to secure the new alignment.

So that's all folks and I wish you good luck

George Nikolidakis

       Fig 8

Fig 9                 Fig 10

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Last edit: 07.05.2001 .