Celestron Nexstar SLT 127 MAK - Alignment

[Rajeev]

Hi Folks

My 6 month old (used 4 times) Celestron Nexstar SLT 127 Matsukov Cassegrain has always given alignment problems. It is difficult to align and once aligned, quickly goes out of alignment. Just this evening after using the Solar system align using Venus, I selected Mars (which is very close to Venus these days). The scope went about 5 degrees south of Mars.  When I sent it back to Venus, it didn't go there either.

I have had problems with the two star align as well. Once aligned, it held Saturn for about 15 minutes before going out of the field of view, but when asked to go to a different star, it gets quite lost. Sometimes it goes below the horizon looking for things !

I don't know what to do. Returning is not easy given that I am not in US

regards

Rajeev

Kingston Jamaica

[Cosmic Geoff]

It's possible that there is a fault, but first check all the things you are advised to do in other posts on GoTo problems.

Is the tripod levelled with the bubble level? Are the latitude and longitude entered in the proper format?  Is the correct time zone & daylight saving entered when entering the time?  Is the +12v DC supply stable? Most users abandon the internal batteries in favour of an external supply, but it is then essential to watch out for problems with the external power plug which can give poor contact. There are various things you can do about the power plug, including running the cable through a cable tie stuck to the mount, so that when the mount moves around and tugs the cable, the cable tie and not the plug takes the strain.

A wrongly entered date or Lat/Long could cause some of the problems you mention.

[ronin]

Would suggest to not use a planet for alignment. Reason is that the stars have a position that is effectively fixed from year to year, or century to century. Planets are not fixed and so in order to determine their position the system has to calculate their present position and that leads to small inaccuracies accumulating. Since the starting RA/Dec was from a batch of data that could be 10 or 20 years old. In effect the scope is trying to work out where Venus is now from what could be data 10 or 20 years old.

Check the power, they are a bit of a pain with regards power. They are rated at 12v but I have heard that 12v is a bit low, equally they have little protection in them so if you feed in 13.2 volts you could blow something. Batteries will start to drop the voltage almost immediatly they get used.

No idea which is better 2 or 3 star alignment, should be 3 but people have had trouble with 3 star alignment.

15 minutes in view is in my opinion good, the scope delivers higher magnifications so smaller fields and the planets move at a different rate to sidereal.

For alignment use a 30mm plossl initially and they are good for use each time a goto is completed, for you to get the object in the middle, I went and bought a 40mm plossl the morning after I bought my Mak.

The better the initial setup level etc the easier the scope will do things. If the scope is level then the softare has a smaller or lesser compensation calculate and then apply.

There is hidden well in the depths of the software an option to perform a "synchronistaion". This is like telling it to goto Betelguese, centering Betelguese then performing the Sync and the resets it's present position to that of betelguese. When you think about it the scope goes to something - as far as it is concerned that is it, it is where it should be. You then center the object but the scope counts that "centering" as movement from the specified position. The sync action simply tells the scope to forget where it thinks it is and use the position of the selected object as the position. The problem is on a Meade the sync is easy, on a Celestron it is not so easy, or may not be as easy. Have a read of the manual.

[Cosmic Geoff]

I disagree about 15 minutes of tracking being good. I've found that my SLT Goto will track for hours. I tried it once against the EQ5 with RA drive and the SLT won hands down after both were left unattended for two hours.

The 3 star align AFAIK is no better than 2 star - the difference is that with 3 star the mount identifies the 3 stars, with two star the user has to identify at least one.

[jimbo747]

Are you using batteries? My SLT tracks jupiter or the moon for hours, I can even park it and turn on next day and tracking is still bang on.

 

I always do 3 star alignment.