dovetail alignment ??

[hemihaggis]

hi folks , i have a meade sn10 with ldx 75 mount , which i purchased second hand for buttons , as it was broken , the ra motor was burned out , and the rest was in bits and a bad state of disrepair , i have fixed replaced ,bodged it back together , but my goto seems to be off in some sections of the sky and not others ,

i have aligned the polar scope to the mount ,

but do i need to align the mount to the dovetail ? or the rings that hold the scope ?

i have tried 1,2 and 3 star alignments , first it slews to vega ,always misses ,so i unlock the clutch and center , then it will pick mizar ,again misses , so i center on mizar , and it says alignment succesful , i then ask it to find vega ,and it will be just on the edge of fov , then try m13 0r 15 and it will miss it by quite a way , then try vega again ,and it will find it ! slew to m31 and misses ,well off target , then try ring nebula , at edge of fov , double check vega and it close to center ??

any genius ideas ????

[hemihaggis]

help ...... its so quiet out here

[Ant]

Hows your polar alignment? I would think that this is much more likely to be the cause than anything to do with the dovetail alignment (which as there are no encoders on the RA and DEC - the GOTO software doesn't know that you've moved them).

Also make sure that the date and time are correctly entered. Finally make sure that the power supply is good. The HEQ5 / EQ6's are real fussy on the power front - maybe the LXD is the same?

Good luck.

Cheers

Ant

[hemihaggis]

thanks for the reply , i have my polar scope aligned spot-on with the mount , my mount is set up with the date ect on the circles ,transit of polaris ect all looks good , put polaris in circle on polar scope and do two star align , this should be more than accurate enough for visual ... but it well off as above ....

[Martinus]

Hi hemihaggis.

You should not be unlocking the clutch to re-centre the star. When you do this the mount assumes that the last position it slewed to has not changed. Re-centre using the controls on the handbox.

How did you align the polar scope?

If the polar scope is properly aligned and you use the 'Kocab clock' method of polar alignment: The Star Deck Observatory Kochab's Alignment For The GEM

The dovetail does need aligned but I consider the dovetail that comes with the scope to be pretty poor - cheapo cast aluminium that's soft and chews up when you tighten the screws. Replacing it would be advised if you can afford to.

I will admit that I've only ever had reasonable performance of the GOTO with the SN-10 mounted. It's simply too heavy a scope for the mount.

I suggest you pick up the following book: Amazon.com: A User's Guide to the Meade LXD55 and LXD75 Telescopes (Patrick Moore's Practical Astronomy Series) (9780387364896): Martin Peston: Books It's a comprehensive book that should allow you to get the best out of both the scope and mount.

[Merlin66]

Could be "Cone Error" where the optical axis of the telescope doesn't align with the mechanical axis of the Dec shaft.

On many dovetails there's an extra two small screws below where the scope rings attach - ever wondered what they were for?? Well these are used to re-align the scope with the axis and remove Cone Error by slightly tilting the rings/ scope to compensate.

A Simple Cone Error Correction Procedure - How To

HTH

[soggybongo]

I know this is a little late but i have just adjusted my rings on the lxd75 mount.

To accurately polar align the mount with the North Celestial Pole the polar viewfinder

has to be in perfect alignment with the RA shaft.

if you have done this correctly, whatever you look at through the polar scope will stay within the little circle and not alter position when you unlock the RA shaft and move it.

If the object moves when you rotate the RA shaft then you need to adjust the three little grub screws on the polar viewfinder.

In order to obtain good pointing accuracy during tracking and Goto operations, the

OTA needs to be physically aligned in parallel with the RA axis. Also the Dec axis

needs to be calibrated with the Dec setting circle.

If you need help with this P.M me and i'll happily explain.

[Tinker1947]

When you align to a star the mount has chosen, center it and then use a high power EP to get it spot on....