Aligning polar scope

[dawson]

After spending over an hour the other week trying to align my polar scope to the mount, and after pulling out what little hair I have left (arm pit, eye brows), I decided their must be an easier way as the little grub screws holding the polar scope reticule in place are so small and sunk into the polar scope mounting and need an hex key to alter them (undo two, tighten one; undo another one, tighten the other two....)  AAAAAGGGGGGHHHHHH  Any my neck was killing despite the mount being at full height and the dec set to about 10 degrees above the horizon.

 

So, I fired off several abuse text messages to Felix to vent my frustration and he suggested I get some grub screws with thumb grips on.

 

I found some on ebay (3 for £1.20 I think) and being sold just for this purpose.

 

I've just changed the existing grub screws for these, and I have to say aligning the polar scope has been so easy (but still a pain), but much much quicker and FAR FAR easier.

 

This was the ebay item but it seems he has run out. You can probably get 10 million of them from screw fix for the same price, but at £1.20 and free P&P I didn't care.

 

Here is the polar scope with the new screws. I'm just waiting for Leigh to come over and have a look through to see if he thinks it's aligned too or not. (It's also very hard to keep your head/eye still as you rotate around the RA axis).

 

James

Edited May 19, 2013 by dawson

[dawson]

The guy recommends putting a blob of superglue on the join to stop slippage, but Felix says he hasn't and I agree that they feel firm. I think if they do slip I will do that next time.

 

James

[dawson]

For the Skywatcher polar scope mounts, they are M3 screws, and mine are 10mm long, but the 8mm ones would still work and be less proud; I think any less than 8mm would be difficult to use as there is a slight shoulder which would knock against the thumb screw head.

 

James

[Brantuk]

Not to rain on your parade James - but you might still find some error remains if the rest of the mount isn't set right. They are the polar scope collimation screws, and though the polar scope may be aligned with the mount - the polar scope itself might be out of collimation......

 

You need an "L" bracket to check the collimation of the polar scope.

[catman161]

I think he was just realigning the reticule Kim as it had fallen out. As its a brand new mount I can't imagine the polar scope itself is out by much? Unless of course you have removed the entire polar scope since you bought the mount James??

[dawson]

No, I've not taken the polar scope out; I don't know how but I might have a go now to see what it looks like

 

No Kim, I wasn't expecting to get unguided tracking for 30 minutes now, I just wanted to reduce my polar alignment errors as much as possible, and as Felix said, the whole reticule fell out (I didn't really remove all three screws at once) and it was so out of alignment with the mount, I might as well have pointed it south and the polar alignment would have been as accurate

 

If we get a glut of clear nights I will try the drift align thing, which I know nothing about, but I superficially believe will give me some idea of how good or not my polar alignment is. Yet more of Dion's videos to watch ("Hello again").

 

But for now, I'm happy I'm starting from an OK position; apart from the cone error.

 

James

[Brantuk]

I wasn't going to mention drift aligning - but when you've mastered it you can show me how to as well. lol

[Orion]

I wasn't going to mention drift aligning - but when you've mastered it you can show me how to as well. lol

As far as I can remember, you choose a couple of stars (separately), and have dec set at 90deg. Watch the star drift with the RA off. If it drifts N, do an adjustment on one axis (can't remember which), and watch again. If it drifts S, you've gone too far. Interpolate adjustment in between. When there is no drift, one axis is aligned. You do this for the E/W alignment with the other star (chosen as a different place in the sky best suited for that axis). Once aligned, with RA on, the star should sit neither drifting E or W nor N or S.  I think it's something like that.  Ron Arbour did a good article on alignment in Sky and Telescope quite a few years ago, using film to show the star trails you get both with and without RA on.   I have the article but can't find it. I have a copy of another version of the method somewhere but you may already have it.  I don't think it's a timely investment method if the scope is taken down each time because the alignment has to be done every time unless the scope is in an observatory.

[dawson]

Sounds complicated.

 

I think I'll stick with crappy polar alignment

 

James

[Orion]

[Brantuk]

Thanks Derek - I'll try and remember that but the odds ain't good lol.

 

(I'll download Ron Arbours article)

[dawson]

I seem to recall Ron telling me about drift aligning when I went to visit him, but he saturated me with so much information my brain overheated I think he was telling me to just leave the scope tracking, with a star on the cross hairs of the reticule of something like backyard EOS, and the star should do something, but I can't remember what. I'll ask Ron to contribute.

 

James

[+RonC]

Try this video from Ast Shed http://www.astronomyshed.co.uk/forum/viewtopic.php?f=19&t=3867

Explains it better than I could!

 

Ron

[Orion]

The star will drift either N or S of the cross hair horizontal line if the alignment is out. You can then make the appropriate adjustment for the N or the S. Then recenter the star and watch it drift again. To be quantitative, you time the star to see how far (or how long) it takes to drift. You'd need a reticule with some divisions on it to be able to see how long it takes the star to drift a given distance. If the drift takes longer, you're closer to alignment. You can then interpolate between the measurements for the next incremental adjustment to be made.  Once the star sits on the line and doesn't drift N or S after a reasonable time, then you've done it.  I can't remember how the E/W is aligned/adjusted, but I think a similar way.  I'll have a look at that video in the AstroShed.

[Orion]

Thanks Derek - I'll try and remember that but the odds ain't good lol.

 

(I'll download Ron Arbours article)

[philjay]

If you are just doing visual James then dead accurate polar aligning isnt really that necessary and drift aligning is just OCD.

My heq5 polar scope is aligned so when I use it for visual I just make sure polaris is somewhere near the middle, if I want to waste observing time I set it using the reticule but there aint a great deal of difference between the 2 methods and even if there was a tweak on the handset button soon brings the object back into the centre of the fov.

Its very easy to get bogged down in technicalities when sometimes it doesnt really matter that much

However if you are after accurate unguided tracking for as long as your mount will allow then aligning the polar scope, getting accurate pa using the scope and then drift aligning is essential. But by the time youve got that right its probably clouded over and youve missed the clear skies :-)

[dawson]

That time I used the mount at Wymeswold when Mike set it up for me, I managed to get 6 or 7 minutes of unguided images when I was messing around with the Dumbbell Nebula. I've only had the mount out four times since, but each time the polar alignment hasn't been anywhere near as good. I've since aligned the polar scope with the mount, and now I understand how in principle to do a better polar alignment that before (without drift aligning). So, I'm hopeful next time I'm out I can polar align better and quite quickly, before the clouds set in....

 

James

[Orion]

I guess accurate polar aligning isn't needed or not so demanding with modern CCD astrophotography where relatively much shorter exposures are needed compared to film - where only one frame was taken over a long period, and without autoguiding methods but standing there keeping that guide star on the cross. My recollection of alignment by drifts methods was in the days of film work.