Polar Alignment, where am I going wrong

[Glenhuon (Bill)]

I've just spent another 3 hours trying to drift align my EQ5 GEM following the How To from the articles section. The mount is level and roughly set to true South with a compass, I set the reticle so the RA and Dec adjustments track down the lines, find a star to the west and adjust the altitude so the star drifts straight down the E/W line on the reticle. So far so good. Then I find the star on the meridian to adjust the azimuth. Thats when it goes pear shaped. No matter which way I swing the mount it seems to make little or no difference to the drift. I'm going wrong someplace. Help!

Bill

[JohnH]

Bill,

It sounds like you have not made the correct adjustment there should be no drift once the mount is correclty adjusted...unless you are referring to the slow E-W oscillations due to PEC.

What I do is :

Get your mount level - not to critical but get close.
Get your mount to point S using a compass - remember to offset for Magnetic VARIATION in your area - you need to point TRUE S not MAG S.
Set the ALT scale on your mount to match your LATITUDE.

Now slew to a star on the Meridian in the N (or close) and adjust youe AZ settings to remove drift.

Finally do the ALT setting using a start in the E.

This might help too:

http://www.petesastrophotography.com...alignment.html

[edwardsdj (Doug)]

Hi Bill,

When you say "No matter which way I swing the mount it seems to make little or no difference to the drift" is the drift always in the same direction?

My gut feel (as JohnH is suggesting) is that you are initially pointing at magnitic South and not true South. Consequently, you will have to make a large adjustment in azimuth in order to become aligned. You are probably making small adjustments around magnetic South and not seeing much difference.

Hope this helps.

Have fun,
Doug

[Glenhuon (Bill)]

Just rechecked the initial settings, alt was set OK at 34 deg but az was way out as suspected. Reset using compass and length of wood along the east/west tripod legs with 11deg offset to my left looking south. Should be close enough for starters. Now all I need is a clear sky to try it out, thats the hard part

Cheers
Bill

[Zuts]

Originally Posted by Glenhuon

Just rechecked the initial settings, alt was set OK at 34 deg but az was way out as suspected. Reset using compass and length of wood along the east/west tripod legs with 11deg offset to my left looking south. Should be close enough for starters. Now all I need is a clear sky to try it out, thats the hard part

Cheers
Bill

When i was starting out and just to be sure, i used to plonk it down in roughly the right direction then make quite large adjustments until the direction of drift changed from Nth to Sth. Then I knew I had at least crossed RA for SCP and would begin making the finer adjustments.

Paul

[edwardsdj (Doug)]

Originally Posted by Zuts

When i was starting out and just to be sure, i used to plonk it down in roughly the right direction then make quite large adjustments until the direction of drift changed from Nth to Sth. Then I knew I had at least crossed RA for SCP and would begin making the finer adjustments.

This is still how I do it. I always try to find two azimuth positions with the drift in opposite directions and keep refining to the desired degree of accuracy.

[Zuts]

Originally Posted by edwardsdj

This is still how I do it. I always try to find two azimuth positions with the drift in opposite directions and keep refining to the desired degree of accuracy.

I usually still do it as well, it gives me confidence that I am at least in the ball park.

I think what happens is that when you start out everything re drift aligning is a mystery. You get used to doing it a certain way and after a while it is no longer a mystery and you just do it

Just keep at it Bill and eventually you will get there

Paul

[Glenhuon (Bill)]

Without moving the tripod legs the EQ5 has limited adjustment in Azimuth, so you have to be in the ball park to begin with. Mine was somewhere up in the stands
I think what I did was offset for true south in the wrong direction when I initially set it up. I'm getting the hang of it, just need a bit of practice.
Thanks for the advice gents, its much appreciated.

Bill

[Zuts]

Hi,

I do move the legs. After finding a star and checking which way it is drifting I grab the whole kit and kaboodle and rotate it maybe an inch or two. Then find a star and look for drift. Then move it again find another star and check for drift. Once it starts drifting the other way i move it back a little bit and then start using the adjustment knobs. Before I start i ensure that the mount head is in the middle of the adjustment range.

Remember, it may be a precision optical instrument/mount etc but really it is not made of feathers and is quite strong and short of having it tumble over is quite hard to damage.

I dont have a permanent setup so have to start from scratch in the park each night i want to image.

Thats how i do it anyway, your mileage may vary

Paul

[Glenhuon (Bill)]

No permanent setup here either Paul, but I have a spot in the garden where I can see most of the West a bit of North and another for East and the rest of North (lots of trees around). Once I get the mount aligned in each spot I intend putting some cement filled PVC tube into the ground with indents for tripod feet. That will give me rough S alignment when I cart the mount out of the shed and plonk it down.

Bill

[edwardsdj (Doug)]

Yeah, if you can mark or remember the position it helps heaps.

I have the wedgepod. It was a really budget mounting option for the C8 in the late 90s. At the time this suddenly made the C8 affordable for me. The wedgepod has no fine altitude or azimuth adjustments at all so I have no choice but to rotate the tripod

[Glenhuon (Bill)]

I did a Google on the wedgepod and found this page where the owner had modified it. Would only need minimum tools and most of the materials he used are available from the local hardware shop.

http://members.aol.com/__121b_u5kDZQ...ORa3J/TkygTDIj

Bill

[edwardsdj (Doug)]

Hi Bill,

Thanks very much for that link!

Several really good ideas there

Have fun,
Doug

[Glenhuon (Bill)]

Just taking some pics of M42 (Orion Neb) at 60 secs exposure, tracking 100 times better. Thanks for the help gents

Cheers
Bill

[Glenhuon (Bill)]

Images turned out much better for exposure but got spoiled by heavy dew on the objective . Next purchase is a hair drier

Bill