Nexstar 8 alignment problems - 2Star vs Auto

I have been having trouble getting any good alignment on my Nexstar 8. I have tried both the Auto Align and 2 Star alignment methods and the resulting goto's never place the object in the eyepiece (32 mm). (and sometimes around 5-10 deg off).

I have made sure the telescope base is level,
Align the stars with a 9 mm eyepiece,
Pick stars between 40 to 80 deg apart
Use the AC Adapter to ensure it is not poor batteries,
Tried various and different stars for alignment.


For those in the know, a few specific questions...

*Do I need to get a wedge to get better alignment on the goto? Would it make any difference. (or would it just make it even harder to get an alignment)
*Should there be any difference between the 2 star and auto alignment results? (I often use the 2 star since that eliminates location/time/date errors.)
* Do I need hyper accurate level on the base? There is no good spot to place a level on the base, so I have used various methods like using a small level that fits on the battery lid, leveling the tray below, using the same length tripod legs on a level surface...

Any other suggestions?

Thanks

Geoff

Geoff,
First, I have also experienced problems in the past that were repaired by replacement of the scope. Sending it in did no good as it returned with the same problems.
The leveling can be done by placing a round bubble level on the mounting base of the tripod before mounting the scope fork. These are available for about $3.
I always use the GPS alignment, just because it works, but I have used the quick alignment for Sun observing with good results.
The Go-to will always bring the object into the FOV on the 32mm EP that I use, usually close to the center of the FOV.
A wedge is not needed to get an alignment or for Go-t to be accurate.
One thing I did find helpful was using a X-hair EP for the 2 start alignment. I found that accurately fixing the star in the center of the FOV made the Go-To much more accurate as well.
Hope this helps.
Floyd

Geoff,

I've had better luck picking stars that are both on the same side of the meridian. With two star alignment at this time of year at my location, I use either Altair and Deneb if it's early in the evening and they are still above 20 degrees, or Capella and Rigel if it's later. Generally this gives me decent results, i.e., targets are always within a 40mm plossl, and usually within a 25mm. I don't have a wedge.

I read somewhere to avoid using Polaris as the first star; not sure if this is true, though.

I don't notice any difference between 2-star and auto align, FWIW.

I don't think it's necessary to be super accurate levelling the base, but it should be pretty close. I check with a small level along each of three axes, on the diagonal across from one tripod leg. I think what is important is that the OTA be orthagonal to the azimuth axis of the tripod, which is easiest to do if the tripod is already level and then the OTA is levelled on it.

Because of backlash, it seems to be important that the final movements in aligning the star mimic the final goto movements when the scope is slewing itself. Since direction changes between slew settings 1-6 and 7-9, you have to figure how to mimic the scope's final slewing behavior with the keypad (this varies depending on whether you use a diagonal, etc.). Experiment a bit and you'll quickly figure it out.

Is there any chance the clutch is slipping on your scope? This will ruin alignment.

HTH, Eric

Hi Geoff,

If you can align with a 9mm eyepiece you should have no problems. I usually use an 18mm radian. I use a cheap bullseye level on the battery cover. I use Polaris as an alignment star from time to time. Never have had a problem...except when I've entered bad data.

If you're off by 10 to 15 degrees its sounds like a data entry error may be your problem. DST vs Std Time? Time Zone? Storing the wrong lat/long in the "0" memory location?
Or whatever location you're using.

If you've tried all this simple stuff, then I'm at a loss.

Pete

Thanks to all, I finally got it working. I think it was a combination of taking too long to align the stars and the backlash.

Last night I had everything ready before starting a 2 star alignment (star choices, eyepieces, focus, ....) I also made sure to finish each align star using the up and right arrows (same direction when the scope finishes a goto). The objects I tried all appeard within the eyepiece.(32 mm) I used Rigel and Pollux and found that for objects around or 'between' the two stars, the aligment was better. A goto for farther away from the align stars seemed to be worse.

For Mauricio, the backlash effect is like the 'wiggle room' in the gears. If you are slewing to an object and change the direction of slew to the opposite (say up then down) you can hear the motor moving for a few seconds before the image starts moving (at slower speeds). You can imagine that the gear has tension on one side, then as you reverse direction, it unwinds the tension and then builds it on the other side of the gear before it actually moves. The net effect is some indeterminace in a position with respect to the gearing.
Not sure if that is exactly correct, but it is my understandign anyways. :-)
Not sure what to say about the photo's, but with the alignment last night, ojbects would mostly stay within a 9mm eyepiece after they were centered.

Thanks again to everyone that chimed in!

-Geoff