getting an eq6 accurate on goto

[LeeB]

I am hoping this post will help afew people suffering from inaccurate goto mounts, mines an eq6.

I recently upgraded to a synscan and have been a little upset by its lack of accuracy on finding objects from different portions of the sky.

The following is my step by step proceedure.

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I tried to elliminate each error in turn.

polarscope align ---- check

mount level------------ check (don't trust the bubble on the mount mine was off)

polar align perfectly--- check

retest whiole set up and still not good (depending on the area of sky up the half a field of view out at 75 mag.

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checked for mount cone error normal way ( results indicate a fault)

so checked using a laser ij place of a scope and a target at 50 feet ( target consisted of two x 's exactly a distance apart to coincide with the distance the laser moved when slewed 180 degree in RA.

(mount was spot on no cone error)??

Checked scope for cone error ------- fault indicated. ( ie. optical path does'nt run straight down centre of tube)

I must point out at this point that its collimated perfectly.

Checked scope again in a pair of v cradles and spun, error, funnily enough more than half field of view at 75 mag.

Checked in mount , when the tube was not spun to allow easy access to eyepiece the three star alignment to elliminate cone error worked and the accuracy was ok.

But its a newt and you spin it in the cradles. so the cone correction by three star alignment was making it worse.

Recollimate the newtonian , this time primary first with laser replacing the secondary to align optical path to tube , then adjust only secondary to get perfect collimation. ( this requires using the spider the move the secondary as well at the screws to set angle.)

retest in jig and spin tube , spot on no cone error with ota.

retest in mount, Eureka!!!!!

it works on one, two and three star alignment and was near perfect.

Have now realigned three newts and all showed error in the same goto mount until optically aligned with tube.

Hope that helps ....