The method has evolved over time of course. In particular, Robert Fields and Ralph Pass were involved in the discussions at that time and made contributions to the method.
More recently, Philip Perkins (email@example.com) posted an excellent message to MAPUG on 9 Jun 1996 regarding the procedure he uses to achieve Polar Alignment. I have included an excerpt from that post below. (I have omitted his steps 1 through 4 - they cover other telescope adjustments such as leveling, setting geographical coordinates, setting time, etc. You could refer to the MAPUG archives or perhaps send him E-Mail for that information.)
What I refer to as "iterative alignment" corresponds to his steps 5 through 8 in the excerpt from his post below.
I have used iterative alignment for all of my photographs since December 1994. I use only the 26 mm eyepiece for this and center Polaris and the "other" star by sight. I used to think that I needed to put in the 9mm eyepiece with reticle and work to get it REALLY, REALLY precise but I have found that not to be necessary even for 3 hour exposures.
a. Polar alignment is a complete process involving all steps 1-5, so this step assumes that all previous steps have been completed.
b. The tripod is already level and doesn't have to be shifted further to achieve polar alignment (fine adjustments can be done with the azimuth control).
c. You have a viewfinder of some sort (although this is not used for actual polar alignment).
d. You have a RA prism for the main telescope.
e. You have an illuminated reticle eyepiece. Seems a lot of people use a 9mm - OK, but this degree of magnification is not necessary (and may even make the process harder). I use a 12.5mm and this works fine.
f. You have 3.34 ROMs fitted to the LX200.
- "Mechanical Adjustments" - make adjustments using the Azimuth and Latitude control knobs on the Superwedge, only. Do not touch the keypad controls.
- "Keypad Adjustments" - make adjustments using the N,S,E,or W keys on the LX200 keypad. Do not touch the mechanical adjustments on the Superwedge.
Before starting ensure that the LX200 is firmly bolted to the Superwedge and that the tripod is level.
1) Align the finder with the OTA. First, fit the RA prism and illuminated reticle eyepiece to the telescope. Centre a reasonably bright star in the main eyepiece, then adjust the finder collimation screws to centre the same star in the finder. This is not a critical adjustment - it just helps in getting Polaris into the FOV of the telescope.
2) On the Keypad, select Telescope - Align - Polar. Set the Declination of the OTA to 90 deg and RA on the drive base to 00, as described under b) Polar on page 31 of the LX200 manual. However the description of the RA setting in the manual is somewhat obscure.
- Declination setting: rotate the OTA until pointing roughly toward Polaris. Then accurately align the OTA until the Declination Circle reads exactly 90 deg. Use a magnifying lens to accurately align the 90 deg mark with the pointer (I use a magnifier with integral red light). Don't be tempted to set this to 89.2 deg - you're aligning on the celestial pole, not Polaris - the LX200 knows the exact position of Polaris and will move the OTA to this position at the next step. Lock the Dec drive.
- RA setting: quite simple really - you are aligning three things:
1) The pointer on the upper (moving) part of the fork arm base.
2) The '00' mark on the RA setting circle.
3) The pointer on the lower (fixed) part of the drive base. First, align the '00' mark on the RA setting circle with the fixed pointer on the drive base. Then rotate the fork arm until the upper (moving) pointer is aligned with the '00' mark (and the fixed pointer). I recommend using a magnifier to check this alignment too. Lock the RA drive.
3) Press Enter on the Keypad and the LX200 will slew round to where it thinks Polaris is. Using the finder and Mechanical Adjustments *only*, bring Polaris near to the centre of the finder FOV. Next, through the *scope* eyepiece, continue using Mechanical Adjustments to move Polaris to the exact centre of the illuminated reticle.
4) Press Enter again, and the LX200 will slew to another star, usually near the southern horizon, for the second part of the alignment process. Use Keypad Adjustments *only* to centre this star in the illuminated reticle, then press Enter.
[Sometimes the LX200 selects a star that is obscured from view. If this happens, press Enter so that the LX200 escapes out of Polar Alignment mode**, then select a bright star that *is* visible, and 'sync' on this - see steps 5 and 7 below, for this procedure]
** With 3.30 ROMs I seem to recall that pressing 'Star' escaped out of Polar Alignment mode, but with 3.34 ROMs no key apart from 'Enter' escapes out of this mode (regression issue?)
5) The standard polar alignment procedure is now complete. Next comes an additional section which yields very precise polar alignment. As a precursor to this section, select a second star for the alignment process.
This can be the same star that the LX200 selects, but doesn't have to be (especially if the star is obscured or close to the horizon). Select a star that is as distant from Polaris as practical, which means that it will be fairly close to the southern horizon (but not so close as to get a significant atmospheric refraction error). Preferably this star will be in the LX200 alignment star library (but only for ease of selection). Just so we're not being too pedantic, there's no real difference to alignment accuracy if the star is a good bit east or west of the southern horizon. For example, in spring or early summer (at +51deg), Spica is a good star to select. We'll call this star the "Second Star".
6) Press Star - Name - Polaris - Goto. The LX200 will slew to Polaris. Note the position of Polaris on the illuminated reticle eyepiece. Draw an imaginary line between Polaris and the centre of the reticle. Carefully note the halfway point on this line. Using Mechanical Adjustments *only*, move Polaris to this halfway point.
7) Press Star - Name - "Second Star" - Goto. The LX200 will slew to the Second Star. Using Keypad Adjustments *only*, move the Second Star to the exact centre of the eyepiece reticle. Then "sync" on it (press and hold Enter button until keypad beeps).
8) Repeat steps 6 and 7 until the alignment error of Polaris is zero, or virtually zero. It should take no more than 3 or 4 iterations. With each iteration the alignment error of Polaris should be significantly reduced. At this point the polar alignment process is complete. The significant differences between this procedure and the LX200 manual are:
a) Don't go back into polar alignment mode each time to centre Polaris
b) Don't centre Polaris each time - halve the alignment error.
c) Don't wait 15 minutes between each iteration
I found a) and c) redundant, and merely add a lot of time. Also by not going back into polar alignment mode you can choose the second star. This method is a lot quicker than any other 'refined' method I've tried - it's sufficiently quick that it can be used before every observing session where a high degree of alignment accuracy is needed.
With this procedure I regularly achieve very precise polar alignment that cannot be further improved by the drift method. For example, with the illuminated reticle eyepiece (x200) centred on a star such as Arcturus I record no measurable drift due to polar alignment error over a period of 90+ minutes. This is perfect for astrophotography.
Two further things that need to be done for optimum guiding: Periodic Error Correction (under "Smart" menu) and Declination backlash correction ("Backlash" menu item). The procedures in the LX200 manual work fine for me, except don't make any N/S corrections during PEC training. Rotate the reticle so that any N/S drift occurs down the vertical centre line (but if done after the above procedure there should be no N/S drift anyway:-)
Feedback from Dick Green
> With 3.30 ROMs I
> never achieved good polar alignment using this same method, so
> I believe that 3.34 ROMs are very significant.
I believe this is due to the positional errors in the alignment ("named") star database in versions prior to 3.34. The precise alignment procedure you describe at the end will work on older versions with the 64K database if you select Polaris and the alignment star from the SAO database instead. Polaris is star 308 in the SAO database. I believe Spica is 157923 and Arcturus is 100944 (this is from memory, so probably not accurate.)
PP>>> Excellent feedback. There must be many users worldwide still on earlier versions who could benefit from this.
Copyright 1997, 1998, 1999, 2000
Howard C. Anderson
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