Celestron Nexstar 127 SLT faulty goto?

[ShellShock]

I have had my telescope since November last year, and I have never got it to goto with any accuracy. I am trying to be more careful in my alignment process each time I use it. Last night I did an auto two star align on Polaris and Betegeuse. Location, date and time correct (OK I have since discovered that the time was out by 10 seconds), tripod was level. After aligning on Betelgeuse, I did a goto to M42, which duly missed; using an 18mm EP, M42 was just outside the FOV. I then did a goto to Jupiter, which was way off.

I recently updated the HC and MC firmware, so I don't think that is the problem.

Am I doing something wrong, or is there a problem with the mount?

[Steep]

I always use three star align, even with that my SLT is not very accurate but does get the star I want close to the center of the fov. To miss M42 coming from Betelgeuse by as much as that something must be seriously out of whack, either on the scope or the setup.

[ShellShock]

Yes that is what I thought; they are so close the goto should be better.

I have checked my lat and long twice in Google Earth. Date yesterday was 02/02/2013, so I could not mix up day and month (why no international date format option Celestron?).

Could it be the weight of the EP? The stock EP weighs 1.5 oz, whereas the one I was using weighs 7oz. Also I use a Telrad rather than the stock finder. Next clear night I am going to devote some proper time to getting the goto working, rather than being distracted by the sights. If I still can't get it working then I will contact FLO who supplied it.

[Steep]

I regularly use mine with a Baader Hyperion Zoom which is like a small grenade and also have a Telrad on it. I did think about the date thing since it's a common mistake but your SLT wouldn't star align with the dates wrong so that's not it. I'm sure I've read on here somewhere about the gears in the GOTO being too tight in some versions, does your SLT sound like it's struggling when moving in a particular direction? Again mine is quite noisy but I think all GOTOs are.

[CSM]

It actually quite difficult to accurately center the stars as I learnt from webcamming. I would suggest that once you have got your first star in the center with a low power eyepiece, defocus it to get a larger image and see how that looks. Then change to a high power eyepiece and do the same again and repeat for both stars. Also, use the best alignment stars for your time and place as given by the Select Alignment stars program which you can get from the NexStar Resource site

[ronin]

Really I suggest that you check the instructions and every bit of data and make no assumptions.

Just about every problem with a goto comes down to what data is supplied to the system, computers are annoying beasts.

Have you entered the timezone, is DST Off, is Longitude correct - W/E or +/- whichever it wants.

As said assum that the scope has defaults and that not a single one is what you want.

If the alignmet uses Polaris and betelgeuse only then to my way of thinking it is only really one star alignment as Polaris is simply a start position and supplies no data to the computer system concerning the correction that needs to be applied.

[ollypenrice]

Yes, Polaris can provide hardly any information at all in RA because it rotates in such a tiny circle that having it the tiniest bit off centre would totally negate its value. In principle stars closer to the celestial equator will provide the most accurate RA data. Betelgeuse is clearly a good one in that case. I'd pick another on the other side of the sky but as far south of Polaris as possible.

Olly

[knobby]

Agree with you, polaris isn't ideal. Try to use 2 or 3 stars spaced roughly at 3rds of the sky and about triangular shaped ie: Sirius, Capella and something over to the right of the picture below.

Good luck

[ShellShock]

Thanks everyone, maybe it was because I was using Polaris then? I have just checked everything again: I have adjusted where I clamp the OTA so it is more balanced, moved where I tie in the power cable to make sure it is not rubbing on the mount as it turned, checked Lat and Long, time zone are OK, date and time was OK for last night, DST was off.

Next time I will probably use something like Mizar and Rigel. My south is obscured so I normally align and observe from North to East, or high in the south.