Many like myself have found accurate polar alignment very confusing based on various tech “how-to” tutorials found at various places on the web, many of which use refractors. Those of us with variations of Newtonians have it difficult to adopt many of them for use with our backwards and upside-down equipment. I use Envisage to accurately polar align my scope for imaging. Here is how I do it.
First, I would like to say thanks to Claude for developing a reticle that can be downloaded and used with Envisage 7.05. and the DSI II, (there is also one for the DSI I). Go to his web site to download the reticle.exe program. It can be found at this link.
http://lightpollutedskyobservation.generalcybersystems.com/ReticleSoftware.html
Start Envisage and then run Reticule.exe. If you have your DSI II as the first camera on your tabs, you should see the reticle on the imaging screen, (the cam used for alignment must be on the first tab). If your use the DSI II as a guide scope then make it your first tab (leave your DSI III cam unplugged while aligning). It does work with Vista before you ask. Be sure your alignment cam is oriented so that the North/South arrows move the alignment star up and down on your Envisage screen. Your RA controls may be reversed if you had to reverse them to get Envisage to properly guide. On the LXD75, the bottom of the camera should be pointed at the Meade LXD75 inscription on the tube assembly.
As I am setting up my equipment I use the polar alignment scope, (using the procedures in my LXD75 manual), to get a rough alignment. I usually get a pretty good rough alignment using the polar alignment scope. Once you have a good rough polar alignment, (where the star does not drift out of the target circle on the polar alignment scope for several minutes), set your scope to the “home” position as defined in your manual, (in the LXD75 manual it is shown on page 17). The polar alignment scope, (in the Northern Hemisphere), should be pointed at Polaris. However, Polaris is not directly in the “true” celestial north. True celestial north is offset three-quarters of a degree (48 minutes of arc, to be more precise) from Polaris in the direction of Alkaid (Eta Ursa Majoris) -- the star marking the end of the handle of the Big Dipper.
- From the home position, loosen your Dec lock, (the knob on the front of the mount under the tube assembly), and rotate the top of the tube assemble so that it is approximately horizontal, (with the top pointing eastward), or perpendicular to the RA axis.
- From this position we will use two stars to polar align the scope. The first star should be close to the meridian, (directly overhead), and point at or near the celestial equator, (earthly equator extended upward into the celestial sky). From the position that you have moved your scope in step one, loosen your RA lock, (knob on the side of the mount), and rotate the RA axis 90 degrees, (so that the counter weights are horizontal with the ground). The top of your scope should be pointed at or very near the meridian and close to the celestial equator.
- After adjusting focus, use your 497 hand controller and select a star and center it in the reticle cross hairs. And observe the up or down drift of the star being used for polar alignment. Use the RA controls, (right and left arrow keys), to keep the aligning star centered, (for right and left drift), and observe the up or down drift of the star. Be sure that the 497 is set to guide speed, (do this by pushing the number 1 button and it should tell you it is running at guide speed).
- Use the Azimuth fine control screws on either side of your mount to make adjustments for the up and down drift. For example, if the star drifts downward, loosen the right screw and turn the left screw inward in small increments to correct the drift. If it drifts upwards, loosen the left Azimuth control knob and turn the right on inward (clockwise). Retighten both screws. Make only small adjustments and observe the change. I usually center it back into the reticle and observe it for several minutes. If I immediately notice it drifting up or down, I make a further fine adjustment in the required direction. Once you have eliminated all up and down drift, then proceed to the right and left drift correction.
- Loosen your RA lock and rotate the RA axis so that your tube is pointing around 20-30 degrees above the eastern horizon, (your counter weights should be pointing downward at about 70-80 degrees from the horizontal). You should not have to change the declination axis. Find an alignment star and center it in the reticle using the 497 hand controller. Observe the left and right drift. Note: the left/right drift may make it appear to be making the alignment star drift up or down. The upward/downward appearing movement is due to your reticle orientation on the screen. DO NOT MOVE your Azimuth adjustment screws in response to this movement! Only adjust the Latitude adjustment screws, (on the LXD75, these are the T-handle screws on the front and back of your mount). You obviously will have to loosen one and turn the other. Retighten both evenly after making fine adjustments. Adjusting only the latitude fine adjustment should move the guide star back into the center of the reticle. Again, only fine adjustments should be necessary to remove the L/R drift. As you get closer and closer to the true polar north, it should take longer and longer for the star to drift out of the center.
- Note: if seeing conditions are bad, you should note the alignments star jumping all around the center of the reticle. In essence, it may be impossible to get an accurate polar alignment under such conditions.
- Return your scope to its “home” position and proceed to use the two star or three star alignment procedure.
- Shut down Envisage and connect your guiding/imaging camera and restart Envisage. You are now ready to take some beautiful long guided images!
I use the DSI Ic as a guide camera and it guides beautifully after going through the above process. My settings are 2 sec exposures and .85 or so on the gain correction. It usually takes about 45 minutes to complete the drift alignment procedure, but the pinpoint star images you get in the final image for long exposures are worth it.
Good luck and please leave me your feedback and let me know if this how-to was useful to you.
Kaos