Drift alignment and periodic error

[Vega]

Just pondering and now wondering if I've been doing my drift alignment properly over the last year

Here's the thing... I got drift alignment in azm sorted, easy as pie. However when u swing over to the East at a star about 20deg for alt drift aligning I have a small query. If the movement of the star goes up, you adjust the alt bolts so the star moves down. And vice versa if the star moves down, adjust the alt so it moves up. I get that. BUT... is it not true that this star movement is so heavily affected by Periodic error that its just pot luck that you make the right adjustment. I mean, using k3ccd tools, the star moves up and down of its own accord (sometimes by up to 25+ arcsecs) over longer periods (taking in to account that a full rotation of the gears on an EQ6 is around 8 minutes).

I'm hoping you don't all say to me the periodic error movement should be right/left and not up/down. As this means since me using a reflector on this alt drift malarky, i've been orienting the webcam 90 degees the wrong way As much as I don't wanna hear it, please let me know if I was doing it wrong!

Matt

[themos]

when u swing over to the East at a star about 20deg for RA drift aligning

Isn't that for Altitude adjustment, the star in the East/West?

[Vega]

Whoops yes sorry I mean alt adjustment (i've edited the post accordingly)

Matt

[themos]

is it not true that this star movement is so heavily affected by Periodic error

I don't think so. if you turn the tracking to fast, that's the direction of the periodic error, you want to look for movement in the perpendicular direction to that.

PS: Have you seen my video on YouTube on this? http://uk.youtube.com/watch?v=4OtelWKWntc

[Vega]

it's as I feared then... all this time my webcam has been orientated 90deg out on alt adjustments and I've been observing the wrong movements. So this means that on both azm and alt drift aligning, periodic error does not affect the star movement that we observe for adjustments. Great stuff, that means I can drift align as accurately as possible for my unguided setup.

Thanks Themos!

[Edit: Now I think about it, it would have been easier just to ask what orientation people put their webcam at when alt drift aligning with a Newt (Those who drift align with webcams!). My now educated guess is webcam head facing North as opposed to East ]

Matt

[Kaptain Klevtsov]

I just set mine up so that the left / right buttons on the handset move the star left / right. Up and down movement is then what you are looking for.

BTW, if you're using K3CCD try the drift explorer. It takes a measurement and tells you how fast the star is drifting. This gives a clue quickly if you're twiddling it the right way.

Kaptain klevtsov

[themos]

I have the really cheap RA motor for EQ1 which has a knob for adjusting the sidereal rate (smooth changes not 1x-2x-4x). I fear this will make the drift explorer quite tricky to use.

[Kaptain Klevtsov]

Au contraire, use the RA explorer error rate to tweak the drive and the Dec. error to get the alignment. Should be good.

Kaptain Klevtsov

[themos]

KK, I'm all excited now, I better read up on the docs!

[George]

Just turn your tracking off and orientating the webcam will be easy.

[Vega]

Thanks KK. I do use drift explorer, its fantastic and picks up movement that you just wouldn't notice visually. I also use it for PEC training.

I went out last night and had another go at drift aligning. Managed to get both alt and azm staying within 1 arcsec for 5 mins . However I wont reveal my stats for periodic error. Lets just say that the blue RA line on the drift explorer graph was making large mountain shapes! . (saying the words 'guidescope', 'guiding' or 'guidecamera' is prohibited from this point onward)

Matt