PEC... how to?

[joshman]

hey guys, well i managed to get the scope out for a few hours tonight in the light polluted skies of brisbane, i also managed to do a decent polar alignment without an illuminated eyepiece, which is next on the shopping list, (and i realise that there is trailing in my image) which i though was a decent effort, though i have noticed a fairly prominent amount of Periodic error with a 350D at prime focus. so my question is this,

how do i go about correcting this?

preferably with out going down the expensive road (for now :D)

attached is a sample pic of what i'm talking about

350D prime focus through skywatcher ED80 on skywatcher HEQ5 89s, ISO400

(see what i mean about light pollution?)

[vash]

I did this with my EQ6 pro not long ago, (unsuccessfully might add, own fault though)

You will need an illuminated eyepiece though, and a Barlow or 2, ( I used my 5x to do this which worked really well as the PEC was easily noticeable.

Once you set up like normal, would be best to just drift align it, then go to a brightish star near the meridian and center it in the cross hairs.
go into utility functions and choose PEC training and press enter.

select your R.A guide speed I can't remember what they are I think 1 is .25x, press enter on which speed you want (this is just for the button correction speed so it isn't too important but I guess the slower speed would be a little bit better for accuracy).

Once you press enter the controller will beep and your of on a marathon of looking at a bright dot for 10 minutes and 30 seconds for the HEq5 ( 8 minutes for the EQ6) and as you see the star start to drift off the center of the cross hairs press the corresponding button to move it back to the center.

After the cycle is complete the hand controller will beep and your finished. As a warning your first attempt will be crap, so it pays to have a couple of passes at it and this will be helpful as you will start to know where the errors are.

once your happy with it just go back to the setup menu and scroll down to set tracking and select PEC + sidereal. and thats it.

Now I did all this but I made the mistake of disengaging the clutch on the RA and once you do that the PEC is then out, I was wondering why the star kept drifting all around the place, so make sure you use the goto, and park the scope when finished.

[joshman]

oh...ok...maybe i forgot to mention the non-expensive option...

(read: mine is just a straight motorized HEQ% mount, no goto or anyhting, not even a laptop (yet))

[Zuts]

If its not computerised i dont see how you can reduce PEC, short of the obvious which is to strip down the entire mount and regrease it with good quality lithium grease. Also there is a good writeup on cloudy nights about someone who got their not so expensive mount working like a charm, enough to get 3 minute unguided and over 10 minute guided exposures.

try this http://www.cloudynights.com/item.php?item_id=1736

Paul

[joshman]

over the christmas break i'll look into regreasing the gear box, until then, i have negatory time to play with all my toys :(

[Zuts]

Take a sickie :)

Paul

[vash]

whoops my bad,