where to buy an accurate compass?

icytailmark (Mark) · #1 03-01-2012, 01:32 PM

does anyone know where i can buy a good accurate compass online? My old compass broke i dropped it

i need a compass that tells me 12.5 degrees east of south for polar alignment just so my mount tracks.

g__day (Matthew) · #2 03-01-2012, 01:49 PM

Hmm, Sydney - I'd try the boating stores around Pittwater / Newport if you want a really accurate compass. Not cheap but if you want real accuracy - a maritime graded compass will probably be the best you can buy.

Mind you if you drift align - you don't need the expense of a super accurate compass.

icytailmark (Mark) · #3 03-01-2012, 01:52 PM

i only need a good enough alignment for planet imaging. cheers

g__day (Matthew) · #4 03-01-2012, 01:57 PM

Then Dick Smith Electronics or Jaycar will sell a reasonable one for around $40!

Shark Bait (Stu) · #5 03-01-2012, 02:06 PM

I have purchased some navigational items from this business based at Kelvin Grove in Brisbane, QLD.

Scientific Instrument & Optical Sales www.sios.net.au/category/silva-compasses

They sell a good range of silva compasses. I use a Silva Expedition 54/6400 and it is very accurate but not cheap. Sighting compasses make life very easy. It is used for navigating in remote bushlands as well as setting up scopes. It has never let me down and is very accurate. These compasses can also be purchased at camping and disposal stores.

You are probably already aware of this but ensure that it is balanced for the Southern Hemisphere.

icytailmark (Mark) · #6 03-01-2012, 02:48 PM

would any of these compasses be accurate enough?

http://www.raysoutdoors.com.au/onlin...08#Description

http://www.raysoutdoors.com.au/onlin...82#Description

rainwatcher (Peter) · #7 03-01-2012, 03:13 PM

I also use my Silva flat hikers compass. It accurate enough for prep work prior to drift aligning and in most cases when i am just casual viewing with friends and family its fine on its own.

scagman (John) · #8 03-01-2012, 03:19 PM

Quote:

Originally Posted by icytailmark

would any of these compasses be accurate enough?

http://www.raysoutdoors.com.au/onlin...08#Description

http://www.raysoutdoors.com.au/onlin...82#Description

These aren't as cheap as the ones you point out but they are aligned for the sth hemi.
http://www.prospectors.com.au/p-3412...phere-a10.aspx

mikerr (Michael) · #9 03-01-2012, 04:57 PM

Mark, you might be better off using the Solar Noon plumbob shadow method. Very accurate and no compass needed.
AlsAstroClock can be downloded from the IIS files here....

http://www.iceinspace.com.au/files.html

Als files are toward the bottom of the page.

Yell if you need more info to do this setup using Solar Noon.

Michael.

CarlJoseph (Carl) · #10 03-01-2012, 05:58 PM

Quote:

Originally Posted by Shark Bait

You are probably already aware of this but ensure that it is balanced for the Southern Hemisphere.

What does this mean? I thought a magnetic compass pointed north. 180 degrees from that would be south.

Or is there more to it?

skysurfer · #11 03-01-2012, 06:17 PM

For polar alignment you don't need a compass at all.
When there is iron and steel in the neighborhood (telescope tube, mount parts) a compass will get inaccurate.
Just use the celestial south pole or the drift method.
I found out myself an alignment method with a bubble level and a wedge with an angle equal to your latitude. No compass, visible north or south pole needed.

http://sky.velp.info/eqmount.php

Or otherwise google for 'polar alignment telescope'.

Shark Bait (Stu) · #12 03-01-2012, 07:20 PM

Hello Afro Man,

The compass needle (or card) needs to be 'balanced' to suit the Northern or Southern Hemisphere. You are right they all point to Magetic North, but if I take my compass too far north of the equator the needle (or card) is going to be out of balance and drag along the compass housing. To complicate it a little more, some specialised compasses like the Silva Expedition models are balanced for magnetic zones within the hemispheres.

hickny (Peter) · #13 03-01-2012, 08:08 PM

Mark,
You could try here http://www.wellingtonsurplus.com.au/...RION+COMPASSES

naskies (Dave) · #14 04-01-2012, 07:46 PM

I just use the compass in my iPhone and handheld GPS for a rough alignment, and drift align using PHD. My phone's accelerometer (gyroscope?) is accurate enough as a bubble level that I usually just drift align azimuth and leave altitude alignment alone between set ups (good enough for 5 min subs at 924 mm on my SLR).

icytailmark (Mark) · #15 05-01-2012, 03:02 PM

just bought a new compass. Decided to buy this one.

http://www.wellingtonsurplus.com.au/...s+-+Model+9020

just hope its accurate enough.

Shark Bait (Stu) · #16 05-01-2012, 08:02 PM

I think the Silva Voyager Model 9020 looks like an excellent compass. Being Silva you can rely on it being a quality product and if you do have any problems Fiskars will honour the warranty. It is far superior to the cheap copies that are little more than toys.

As you can probably tell, I have an interest in navigation. GPS is a great tool, but when the batteries run out nothing beats a map and compass. I would like to know what you think of this particular model when you have had a chance to use it.

Regards,
Stu.

alocky (Andrew lockwood) · #17 06-01-2012, 01:03 PM

Just saw this thread - I, like almost everyone else in the geological sciences, own a Brunton compass which I've had for over 25 years. Apart from being very accurate sighting/survey compasses, they have an inclinometer built in with a vernier scale. I usually get a rough polar alignment within a couple of degrees with it. However, having seen the price of these things now, you might have to wait for a geologist to die so you can buy one second hand...
http://www.legear.com.au/Brunton-Geo...ton-f-5009.htm

regards,
Andrew.

Quote:

Originally Posted by Shark Bait

I think the Silva Voyager Model 9020 looks like an excellent compass. Being Silva you can rely on it being a quality product and if you do have any problems Fiskars will honour the warranty. It is far superior to the cheap copies that are little more than toys.

As you can probably tell, I have an interest in navigation. GPS is a great tool, but when the batteries run out nothing beats a map and compass. I would like to know what you think of this particular model when you have had a chance to use it.

Regards,
Stu.

Yogie-One (Paul) · #18 07-01-2012, 12:06 AM

For what it's worth, I recently bought a Digital Compas (via Ebay) It didn't cost the earth. At a reasonable cost, it digitally displays to fraction of a degree. When I use mine, I view the telescope from a distance, and line North up with a distant object, with the scope in between. Thus no effect from any close metal. I then line the scope up on the distand object, which is North from the scope.

Irish stargazer (John) · #19 07-01-2012, 08:21 AM

I picked up a map reading compass from Kathmandu (the shop

) a few days ago on sale with 50% off. Its quite adequate.

adman (Adam) · #20 07-01-2012, 09:16 AM

Mark - are you always setting up in the same place, or do you move your gear around a lot?

If you are mostly in just one, or a few places, the solar noon/plumbob method works very well, and you know that it is accurate. I never trust compasses unless I know they have been properly calibrated. My father is a sailor, and from memory, he had to draw up tables of his compasses error for each direction. This not only allowed for magnetic deviation that changes at different points on the earths surface, but also for the local magnetic interference of where the compass was sited - he almost exclusively sailed in steel boats, so the interference was significant. I have found compasses that can be up to 10-15 degrees out.

Another method I have used is google maps. Their grid is aligned (I think) true north/south, so you can project that line onto your observing site, and get within a few degrees.

Hope that helps

Adam