 Supplemental Notes on Alignment Procedure
The following notes are to help improve and/or clarify the discussion by Mike Sparks on
This suggestion is completely optional, and if it isn't needed or desired, then just skip it and stay with the original writeup..... with the previous notes being used. Depending on how good you are at drawing really straight lines and getting very accurate perpendicular lines, you may want to consider these steps as minor alternatives. First, realize that instead of 'drawing' the vertical line, you could eliminate the drawn line altogether and simply buy an inexpensive four foot long straight edge. I purchased one at the local hardware for about $5.00. You could then tape it to the wall directly, with some white paper behind it, just to let the laser beam show up clearly. Next, using a long carpenters level, you could set the straight edge to be very accurate in being level when it is taped to the wall. Reverse the level to assure that it is definitely level. Don't actually put the straight edge in place quite yet, but be aware of how to do it. It will be mounted shortly. Since we're going to begin with a horizontal line that is quite level, and in order to make proper use of it, we need to have a means for making the scope level, right from the beginning. If the scope is placed on a table or stand that is level, we can proceed with this method. The table need not necessarily be level, so long as it is flat, but 'level' would be ideal.... especially for when the line is to be drawn along the fork to be adjusted. Next, insert three screws into the three screw holes in the bottom of the scope. Then set the scope on the table, resting on the three screws. Naturally, make the screws as even in height as can be done by eyesight before putting it on the table. Once there, mount the laser to the top of the scope as described in note #1. Aim the scope at the wall with the laser shining close to level, by eyesight judgment. Now, actually mount the straight edge and make it level, as just described, close to where the laser point is shining. To make the scope perfectly level, we would sweep the beam in azimuth (R.A.) along the straight edge. If the beam tapers from left to right, then the mounting screw on the right side of the scope would need to be raised slightly. If the laser describes an arc near the center of the straight edge, we would adjust the REAR screw up or down as necessary, to move the direction the laser is pointing up or down a bit. There will be interaction between the effects of the screws, but the final goal is to get the laser to be exactly the same height as the straight edge, and have its path to be perfectly parallel to it. This sounds rather difficult, but the first time I tried it, I found it to be just as quick as using the original method. The second time I used it, I found it to be faster than the original method. You now have a horizontal line that is near-perfect in being level, and a scope that is likewise near-perfect in being level. In order to make the vertical line that is perpendicular to the level, take a small washer or nut, attach the end of a piece of sewing thread that is six or more feet long to it, and attach a needle or tack to the other end of the thread. Now, take the needle or tack, hold it against the wall several feet above the straight edge, and let it hang down, with the washer or nut pulling it down. Gravity helped us to make the horizontal line to be horizontal by way of the carpenters level, and gravity is now creating a line that is perpendicular to it. When you run the laser beam up and down the thread, just as you did for the vertical line, you can use the shadow of the thread in the laser beam, showing against the wall, for determining when the laser is following it exactly. In fact, a very small 'niche' or irregularity in the laser beam can be used, and the result is extremely accurate. You may not wish to use this method at all, but you may wish to use part of it. For instance, you may wish to have the scope level, but not use the straight edge. That works too. If so, you can also use a drawn line for the vertical line, and possibly use the 'thread' idea to confirm that your drawn line is truly straight and/or perpendicular to the vertical line. Whatever works. Return to Optical Tube Alignment Procedure, page 3
The first thing that should be pointed out is the fact that there is a slight error in the method of aligning the scope so as to create a straight vertical line. In the procedure, it states that in order to create a straight vertical line at the closest point to the scope, is to move the vertical line, and therefore the OTA ... left or right as necessary, in order to remove the 'arc' in the path of the laser as it is moved up and down. Actually, moving the OTA to the left or right will have no effect at all on the arc. It will only move the vertical line left or right, arc or no arc.
To correct for the arc, what must be done is to change the relationship between the beam path and the mechanical axis of the forks.
Here, we see three angles that the beam might follow, depending on where the laser is aimed, as seen from a top view of the scope. The upper and lower lines are definitely not perpendicular to the bearing axis, and will result in an arcing path of the laser as it is moved in altitude, no matter where the unit is aimed at the wall. The central line is perpendicular to the bearing axis, and will describe a straight line as the scope is moved in altitude, no matter where the unit is aimed at the wall. Our need, then, is to correct for the arc, and also aim the laser beam in the desired direction.
Before beginning either of the following two methods, the laser is first taped so that it is on. The lower two images show the laser mounted as suggested by Mike, and so long as the plate the laser is mounted on can be rotated, it will work just fine. The upper example is another way of accomplishing the task, by using a thin length of wood similar in thickness and width to a wooden yard stick. Two paint stirring sticks glued together at the end will work nicely. The upper unit is assembled by first, taping the laser to the stick, near its end. The stick is then taped to the OTA on the top side, with the laser end of the stick near the corrector plate, and aimed toward the wall. A single piece of masking or duct tape will hold it nicely in place. At the opposite end of the OTA, near the eyepiece end, another piece of tape is applied to the stick to again hold it to the OTA. The beginning point of the taping is such that the stick runs fairly close to being parallel with the sides of the OTA. Now we're ready to make the alignment, for either method. Begin the procedure for the horizontal line, just as described in the writeup. Next, align the vertical sheet of paper as described, until the top and bottom of the line are intersected by the laser. Nothing in the original technique has changed as yet. After having gotten to that point, use the following procedure. Run the laser along the vertical line from top to middle. If the laser strays whatsoever from the line, then the LASER must be re-oriented. If the laser strays to the right and you are using the original mechanics, slightly rotate the laser so that it points slightly to the right. If you are using the 'paint stick' method, then untape the end of the stick nearest the eyepiece, and move that end ever-so-slightly to the LEFT, and tape it down again. (This, of course, also is moving the laser beam to the right.) Then, lock the altitude (Dec) clutch, unlock the azimuth (R.A.) clutch, and move the OTA until the laser again is aimed at the center of the vertical line. Lock the the azimuth (R.A.) clutch, unlock the altitude (Dec) clutch, and sweep the laser from top to center once again. This procedure must be repeated until the laser will follow the vertical line from top to bottom without even slightly varying from the absolute center of the vertical line. You may then proceed to the next step in the original writeup; that of deciding which arm is to be moved, and scribing the original position of the fork to be adjusted.
Return to Optical Tube Alignment Procedure, page 4
After having scribed the original fork position, you are then instructed to move the scope to a level surface for the adjustment. Do so, by all means. However, once you have the scope on that level surface, use your carpenters square and, using a magic marker or some white-out, draw along the fork to be moved, a line from the bottom of the fork to the top! In the procedure, there is no positive check to be sure that the fork doesn't twist. In theory, it shouldn't
matter if one twists some, but in the real world, it matters a LOT!!!!! Once you finish your alignment of the forks,
you will need to go back to these marks to assure that the fork did NOT twist! If it does at all, you must re-align the
fork to the line just described, then repeat the fork adjustment.
This note also may not be better than the original writeup, but I know that for some, making a setup for aligning the OTA to the forks is difficult, just because of having to make the plywood 'wedge' for the procedure. If so, this is an alternate way of mounting things.
Here, rather than tilting the scope, it is stood upright, and the laser is mounted on a camera tripod. There is just enough room to reflect the laser off of the corrector plate and on to a wall, by just missing the edges of the OTA. The laser would be aimed as shallow as possible and off to the side of center. The reflecting beam can reach a wall about 20 feet away, and still be low enough to be able to reach the spots, for marking on a sheet of white paper. Again, if you can use the original way, by all means, do so. Either way, the description on how to accomplish the adjustment, is in the original procedure. Spend as much time as you can on this adjustment to get it as accurate as possible. Many people have since discovered
that it has a very dramatic effect on 'GOTO' accuracy.
I hope these supplemental notes will help in getting your scope as accurately aligned as possible. Bruce A. Johnston Comments and questions are welcome. Please email me at: bjohns7764  |
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