Idea for temporary 'polar scope'

[Stub Mandrel]

Excessive drift on my last AP session shows I need to get a polar scope, and making one seems unlikely to be easy or cheaper.

I've been lining up polaris with the 'middle' of the hole in my mount and this has worked quite well. I thought I'd be clever and guess 1 degree in the direction of Cassiopeia but I now realise I greatly over-estimated the distance it. How to get a more accurate idea of what 1 degree looks like when gazing through a hole?

Allowing for my glasses my eye is about 240-250 mm from the far end of the hole through my EQ3 mount. A quick bit of trig showed that a circle about 3.9mm in radius (7.8mm diameter) would give me an accurate distance from the centre. I've bored a hole in the cap for my mount's centre hole and printed a circle on OHP film and glued it in.

<edit> of course I've just realised I can make a simple;e cap with a hole in it to make sure my eye is reasonably centred.

I can estimate 'just to one side of Cassiopeia' to within an hour or less. Now I know I can't guarantee my eye is dead centre with the tube, but hopefully with my little mod I can do a bit better on my alignment than dead reckoning until Santa brings me a polar scope.

A similar idea could possibly be used to make a stopgap wide-field finder while he elves make a telrad or a big-aperture finderscope* :-)

*I made a finderscope from a cheap 50mm x350 scope - it worked OK but the FOV was tiny, fine for birdwatching, useless as a finderscope :-(

[xtreemchaos]

cool mod mate,i love to hear good ideas. thanks for sharing. charl.

[Gazabone]

Great idea. You could download Jason Dale's app to make it more accurate but I think you would have to add (or subtract!) 12 hours from the clock position the app shows for the correct position of Polaris as I think polar scopes reverse or invert the image; someone please correct me if I'm wrong.

[Tinker1947]

You could use a Telrad, it has a 1 degree circle, you put Polaris on the right part of the circle job done....you also get to use it for star hopping.....

[Stub Mandrel]

Telrad costs about the same as a polarscope - both on the shopping list - but this was quick and free!

[RLWP]

Telrad costs about the same as a polarscope - both on the shopping list - but this was quick and free!

And clever!

Richard

[Steve Ward]

Why not just get somewhere near by guessing and the do a 'DARV' drift-align ... 

[Stub Mandrel]

Why not just get somewhere near by guessing and the do a 'DARV' drift-align ... 

Surely the closer you are to start with, thre better, whatever way you do it? I want to be able to take 2-minute unguided subs and I think this will get me close enough. Long term plan is guiding.

[Tinker1947]

I run through the Handset Polar align routine 2 twice on different alignment stars, but roughly where i intended to images a 3 minute test showed nice round stars (NEQ6 + 250P-DS) .......