Telescope Reviews: Nexstar 8se EQ Wedge Alignment Procedure

Hello Tel, and thanks again for the very kinds words :0) Your NCP question is a great topic to discuss here. I feel the best way to take advantage of polar alignment is to have your wedge as accurately positioned as possible. This will keep the scope tracking on your objects more accurately with little altitude adjustment from the computerized mount.
This is one of the strong advantages polar alignment has over Alt-Az mounting as the Alt-Az computer really needs to do a lot of math to keep an object in view as it passes near zenith. The Alt-Az computer must continually be moving both axes of the mount at continually changing rates to keep the object in view.

Polar alignment fixes this problem but is not always easy to obtain granted that the best indicator we have for the North Celestrial Pole (NCP) is the star Polaris which is ¾ degree off of the true NCP. Several methods were created to properly identify the location of the NCP but require more effort than most wish to endure when setting up their scopes. It seems that most folks choose to align their portable scopes with Polaris out of sheer convenience and forgo the tedious task of finding the NCP.

Unfortunately aligning your mount with Polaris puts a very small tilt in the axes of your mount. This small tilt can cause image drift simply because the mechanics of the mount are not that accurate to compensate for very small altitude movements. This is even more evident when small changes in direction are lost in drive gear backlash. In my opinion you will get the best tracking when the scope is continually tracking with right ascension and having minimal altitude adjustments.

Now it seems the trick is to get proper NCP alignment without spending half the night properly locating it right? Well I feel the Celestron did a great job with their “Wedge Align” function in their SkyAlign software. With this function you can locate the NCP and align the wedge accurately to it with minimal effort. The way the wedge align utility works is the computerized controller (once aligned properly) takes into account where the true NCP should be based on the virtual sky map it generates during alignment. The computer then slews the scope to the direction of Polaris which has been physically offset from the true NCP. In fact the scope will slew to Polaris and it will be ¾ degrees in the opposite radial direction of the true NCP.

This offset that the computer adds to the scopes position compensates for the location of the true NCP and allows you to realign the wedge to point the scope to Polaris (this of course is done without electrically slewing the scope’s mount). Once this alignment is complete the mount should be perfectly polar aligned (3/4 degrees from Polaris to the NCP). You can then perform an EQ north alignment for an accurate polar alignment.

Now the angle of declination for your wedge will always stay the same if you are viewing from the same location. This means that once you set your wedge altitude angle (using the wedge align utility) for your location you should not have to adjust it again granted that your tripod is level. My wedge is set for 34 degrees positive DEC. Unfortunately the wedge azimuth angle which points to the horizontal location of the NCP will need to be set every time you set up your scope. This will need to be done using the aid of Polaris and the wedge align utility.

I personally do not wedge align every time I use my scope. In fact I just level my tripod and use the altitude axes of my scopes to line up with Polaris. This alignment gets me close but is not really that accurate. This is because Polaris is continually rotating around the NCP and depending on what time of day or season you align with Polaris can put the NCP on the left or right (top or bottom) of Polaris. When I align my scope I try to use the position of the big dipper as a reference to what angle Polaris is to the NCP. This helps me to “time” my alignment as to keep it similar to previous evenings. However it is apparent that a new wedge alignment will be necessary as the seasons progress and the NCP will cycle around Polaris as each night passes.

Now I still am impressed with the alignment capabilities of the Nexstar’s computerized mount. Even with simple alignment on Polaris I can get great go-to accuracy granted the scope is positioned correctly on the meridian and altitude index marks before seeking alignment stars. This just goes to prove that Celestron really created a truly dynamic alignment system that can compensate for many variables.

Please feel free to correct me if I haven’t used the proper terminology, I am still learning this stuff :0P

Oh, here are a couple of images I took of the moon for fun....

Thanks for reading and clear skies!!!

Don G.