Compass for aligning.

[batema (Mark)]

I ran an imaging session for my 11 physics class last night that was a disaster. I used an app on my phone to take a bearing of where I wss pointing at home with good guiding and aligned my set up to the same bearings at school. I had to set up before the sun went down and when I tried to drift align before the stidents arrived I was so far away from the direction I should have been pointing phd2 wouldn't drift align.

Can anyone recommend a good compass.

Mark.

[hobbit]

suunto make good compasses

[pfitzgerald (Paul)]

Are you after an app Mark? Or ye old analogue type compass? If the latter did you remember to take into account the magnetic declination for where you are (about 11 degrees). +1 for Suunto.

Paul

[doppler (Rick)]

A quick align good enough for viewing is to set the scope up level and altitude set, then do a 1 star align to a star low in the east or west, then manually rotate the mount head until the target star is in the field of view. Finish with a 2 star align as normal to set the GOTO. Magnetic compasses are hard to use because the metal etc in the mount interferes, My iphone has a compass app that works ok.

[LewisM]

If you use a compass app you need to treat it EXACTLY like a real compass - you hold the phone/compass NO WHERE NEAR the mount, otherwise it will be influenced by the magnetic field of the motors, any ferrous material in the mount etc. IF I use an app, I stand about 5 feet behind the mount and eyeball it. If I use a compass, I have come to know the usual amount of deflection next to my mount, so compensate for it. I made a special plastic jig to hold the compass in a repeatable position on my mount dovetail during setup, starting with a hand held rough align with the tripod, followed by the compass in the jig with azimuth bolt refinement.

I have used both in the field to good success. I also use SharpCap to run an alignment routine to nail it after the rough compass alignment.

I take it you remembered to subtract the magnetic declination from the app display? (silly question,but I have seen it where people have forgotten). One or two of the better compass apps lets you switch between TRUE and Magnetic. No brainer to use TRUE. (as I recall in Sippy Downs/Sunshine Coast area, you need to subtract 11° from the magnetic - compass or app needs to show 169°)

[ZeroID (Brent)]

I do a Google maps or Earth check before I go and get a visual indication of where it lies.
Last effort at Titirangi Beach I just dropped the tripod down, eyeballed it a bit and was within a degree or less. lucky I know but preparation helps. And once you can see a few stars it's easy enough to figure out where SCP is approximately and correct any major deviation.

[batema (Mark)]

I'll go for a suunto. I was just so far off that I couldn't even get go to goimg and tjat was taking into consideration variation. We should get the man arts kids to build us a pad thst would make it so much easier. z

Tjanks

Mark.

[Wavytone]

Forget the compass. Your mount probably has a better solution built-in - the declination setting circle, plus the a=stars above you - and this beats drift aligning too.

My sequence:

1. Level the mount using a bubble level.
2. Choose a bright star on the meridian, near the zenith. Set the dec circle to read the dec of this star, clamp the dec axis and adjust the mount altitude to get the star centred in the scope (at low power).
3. Choose a bright star near the east/west horizon, the lower the better. Set the dec circle to read the dec of this star, clamp the dec axis and adjust the mount azimuth to get the star centred in the scope (at low power).

Check a few stars around the sky to confirm that their decs read correctly from the circle - if not repeat steps 2-3.

Doing this should align the mount on the south celestial pole within the resolution of your dec circle or better, and its a lot quicker than drift aligning. If you have encoders ... nirvana.

There is one issue to be aware of - whether your dec circle and scope are aligned - they may not be. To test this, you set up the scope and do the following in daylight:

a. Choose a target on the horizon and point the scope to this and centre in the FoV. Record the dec circle reading as A.
b. Flip the scope over the mount so its on the other side of the polar axis, and align on the same target. Record the dec circle reading as B. Lock the axis and do not move the scope.

The correct reading is the average i.e. (A+B)/2.

Adjust the dec circle or the scope cradle so that when the scope is on the target, the dec axis reads this value.

[LewisM]

AP 1100GTO doesn't have setting circles by memory

[raymo]

If you have a reticle eyepiece do a manual drift align.
raymo

[Boozlefoot]

Rough enough........ I use this first to get within a degree or two with the scope at horizontal in the dob mount, otherwise scope interferes magnetically, then go for Alt with the inclinometer. Not overly accurate, but enables me to get the sector fairly quickly to start using the finder with illum reticle. Works surprisingly well for minimal cost.

[batema (Mark)]

Thanks for all the suggestions.

Mark.