Need help

mdgodf (Mark) · #1 01-10-2007, 06:59 PM

Greetings,

I’ve been lurking around in the forums and on the site for a couple of weeks now and have gathered some really useful information for getting into this great hobby. But I have a problem (a question really) about rough polar alignment as in the article by Geoff Smith http://www.iceinspace.com.au/index.php?id=63,405,0,0,1,0. For the rough azimuth adjustment I’ve figured out true north after adjusting for mag dec as given for my location on http://www.ga.gov.au/oracle/geomag/agrfform.jsp - 12.516. So I get true north is about 347.5 degrees – correct?

I read another post about a method of finding true north (well south really) using the shadow of a stick at solar noon. So I found out when solar noon is for my location from here: http://www.srrb.noaa.gov/highlights/sunrise/sunrise.html and set up a stick making sure it’s perpendicular and I find that true north comes out to about 342 degrees. So is the difference between this and the mag dec method due to ‘methodology error’ or have I made a fundamental mistake? Which should I use or doesn't it matter that much?

Thanks for your help and thanks to the creator and participants on the site for a great resource!

Cheers, Mark

acropolite (Phil) · #2 01-10-2007, 07:46 PM

I use the stick at solar noon method. Magnetic north varies from one location to the next, I can recall one location, not far from where I live, where compass readings are wildly innaccurate.

Lee · #3 01-10-2007, 08:18 PM

I'd trust the stick too - assuming it was plumb, and the shadow projected on a level surface..... and your time was spot on accurate....

Karls48 (Karl) · #4 01-10-2007, 11:35 PM

Hi, your calculation is correct. But don’t trust the compass, unless you have paid few hundreds dollars for it.

rogerco (Roger) · #5 01-10-2007, 11:38 PM

I'm setting up an EQ5 with drive for the first time, and having similar problems. I used a compass and found my house had been built to what appears to be true north south.

But when I took a few photos I still had problems, I took two shots. The first a stationary shot got me intentional star trails 38mm long. The second with drive engaged got me trails 8mm long. Both were time exposures of about 35min.

My question is is this due to DEC or polar alignment errors (or both).

Regards
Roger Cooper

JohnG (John) · #6 02-10-2007, 08:45 AM

Quote:

Originally Posted by rogerco

I'm setting up an EQ5 with drive for the first time, and having similar problems. I used a compass and found my house had been built to what appears to be true north south.

But when I took a few photos I still had problems, I took two shots. The first a stationary shot got me intentional star trails 38mm long. The second with drive engaged got me trails 8mm long. Both were time exposures of about 35min.

My question is is this due to DEC or polar alignment errors (or both).

Regards
Roger Cooper

Hi Roger

You are going to have to learn to Drift Align if you want to take astro photo's, you require that sort of accuracy to achieve any decent shots.

There are a number of different ways of achieving this, Webcam, visual.

Here is an article from the IIS Projects and Articles page:

http://www.iceinspace.com.au/index.p...63,405,0,0,1,0

If you don't have an autoguider, for shots as long as you have stated, you will need to hand guide by using an Illuminated Reticle and the telescope hand controller.

Cheers

mdgodf (Mark) · #7 02-10-2007, 03:35 PM

Thanks everyone for your comments.

Cheers Mark

CoombellKid · #8 02-10-2007, 04:41 PM

Actually I too think the stick at solar noon is pretty good. Just google
solar noon and it should spit out the info for your location somewhere
in the list of links. I found it is more to do with timing and having the
correct time to align/mark it with. After that and once you have marked
it out on the ground or whatever you can setup during the day and if
need be tweak with drift align.

regards,CS

[1ponders] (Paul) · #9 02-10-2007, 04:57 PM

Getting your azimuth close using the stick is great but it doesn't help your altitude adjustment. Never trust the altitude adjustment readings on the side of your mount. Apart from not being accurate enough in their divisions the scale are more often than not, incorrectly place on the mount head.

If you want to image then you will need to learn to drift align. By all means use the stick shadow to get close, but it won't be accurate enough for imaging.

CoombellKid · #10 02-10-2007, 05:17 PM

Quote:

Originally Posted by [1ponders]

Getting your azimuth close using the stick is great but it doesn't help your altitude adjustment. Never trust the altitude adjustment readings on the side of your mount. Apart from not being accurate enough in their divisions the scale are more often than not, incorrectly place on the mount head.

If you want to image then you will need to learn to drift align. By all means use the stick shadow to get close, but it won't be accurate enough for imaging.

I should of also mentioned, knowing your correct latitude and the use of a
protractor and a spirit level works pretty well

for the altitude adjustment.

regards,CS

[1ponders] (Paul) · #11 02-10-2007, 05:29 PM

Ahhh yes, visual observing. I remember doing that

rogerco (Roger) · #12 02-10-2007, 11:09 PM

Thanks for the replies, I'll ready up on drift alignment and have a go at visual tracking. I was going to get one of those spirit levels that let you set large angles to check the side of ount scale.

Roger