CCD Drift Align (North is South)

[tileys]

Can I just clarify what I think was aluded to in a previous thread(s) (re-read it/them but not 'entirely' certain) but the CCD Drift Alignment method of achieving a price Polar Alignment as seen here:

http://www.cloudynights.com/page/art...ert-vice-r2760

Cannot be taken wholesale as a Southern hemisphere approach as when it says to point South at 0 degrees DEC it should (for us Mexicans) say point North at 0 degrees DEC ?

i.e. you should find a star somewhere in the region of the junction of the celestial equator and meridien (e.g. Arcturus tonight will be on the Meridien at about 10pm - a little away from the equator (abt 20 degrees) but close enough for your Altitude adjustment step ?).

Was given these instructions as a guide for Drift Alignment with no mention of the inapplicability of the second step for our locality and just thought I was missing something (surely 0 degrees South is over there....North ? :-\ )

Wasted the rest of a good evening trying to read up on exactly where 0 degrees DEC actually is in the sky before me - not just on a screen...

I have used Alignmaster and the polar align feature of a handset and it puts me very close but over a series of subs I notice a slight drift and coupled with an imprecise focus my images looked a bit rubbish ;(

Time to tighten up the alignment I thought - but I fell at the first hurdle

[kens (Ken)]

Yes - zero dec is the celestial equator. I've never had a problem finding a star within a degree or two. I just set the scope to 0 degrees using the setting circles and look through the finder for a likely star a little east of the meridian and then down near the horizon

[tileys]

Thanks Ken.

Since I am pretty sure it was already close (from my previous efforts with the Synscan s/w and also with Align Master (I found it a bit hit and miss), I allowed the display of the celestial equator and meridian in Stellarium and just chose a star that looked like it would be a good candidate (Sirius).

I had good fortune with the first set of adjustments - in fact a 120second to and fro showed no deviation (but since I was using Sirius it was actually quite a fat bright streak so prob not the best candidate - certainly for the ISO I was using). Then clouds moved in and I didn't get to do the second set of adjustments

[tlgerdes (Trevor)]

That cloudy nights post is the clumsiest drift method I have ever seen. May as well use an eyepiece and guess how much your star has moved.

[tileys]

I think the adjustments in that post look a bit 'hit and hope' as opposed to calculating with a reticle exactly how much you need to adjust according to a scale but I think as a way of checking how close you are (if you are already set up for imaging) it's got merit.

[tlgerdes (Trevor)]

If you Google PHD and Drift Aligning, you will find lots of better methods that are quicker and more accurate.

I use the PHD graphs and can make iterative changes every 10-30 secs in the first instance, out to every minute as I get closer. The graph gives you intra-pixel view of movement of stars through your guide camera.

You don't even need to know North from South, just follow the red line.

On a clear night I can be drift aligned within 20 minutes from a standing start.

[tileys]

Thanks Trevor - I downloaded PHD the other night (something else to learn so I'll have a look at how it works in there. When the skies clear I'll try to complete the CCD challenge and try some longer subs - see how close it's getting.

If I end up getting an Autoguider I guess I'll have to get to grips with something like PHD anyway though so maybe I have a play with it now anyway.

The alignment option in Backyard EOS is always greyed out for me - I'm assuming that's because it's either a, a trial copy or b, it knows my camera has no live view and that's what it uses ?

Cheers,

[chuckywiz (Ben)]

I find alignmaster to be quite a quick and useful tool.. you just need to input more stars into its database as its a bit lacking. the only other thing i do is tick the box at the start that says move in both axis at same time. or something to fact.

im usually done after 3 iterations with no dramas.

[tileys]

Ben,

I really had mixed results with AlignMaster - even with Peters extended star list (the sterne.txt list) for the Southern Hemisphere I found that I could narrow down the missalignment fairly quickly (within a degree) but then I would have trouble with susequent iterations - some would get slightly closer (e.g. 15-20 mins) while others would get further apart (over a degree again !). I found that a lot of even the extended list would suggest stars that were way down in the sky behind houses or trees and there were some that I couldn't even find with Google (the one with the really long Arabian sounding name I spent one evening going backwards and forwards between Suhail and Acrux and each time it would struggle to get closer. Also - some pairings could be done only in one direction without adding again to the list.

I had better luck (or so I thought) with the 3.37 version of Synscan but that seemed to drift between subs from what I could make out.

I have some good ideas on what to try next though based on the information here though so thanks guys.

[chuckywiz (Ben)]

just a thought when you used alignmaster did you go into eqmod and in the drop down box under sync theres an option for dialog based. if you used the other option youd find alignmaster getting worse and worse.

also tick the box at the start to adjust in both axis. that way all you need to do is centre the star after each iteration.

and as for stars you can always input your own into that list of stars that you can see regularly.. and the one star Rasalmutha somthign or other.. yes took me a while to find.. its not called that hahah

i leave it on dialog based all the time now and find after proper polar align i find i dont even need sync poins at all. i use stellarium and everything is nicely centred in my dslr.

[tileys]

Yes - those are the settings I've got Ben. I'm still at the manual Sync stage though when I have to move across the sky to a new target.

Rasalmutha or whatever lol - yes, that's the fella - although thinking again now - I should have just tried to xref the coords with another program to find out which star it was because it was in most of the pairing options I was given.

Cheers

[chuckywiz (Ben)]

That star is called Atria. its the brighter star halfway between Hadar and the horizon. is easy to spot in the little starfield as even though its not hugely bright it is the brighter one in that area.

once you have your polar align down you prob will never have to manual sync again... i havent done sync points in ages now.

[tileys]

Lol - in that case I have actually used it inadvertently in pairings - that's a good star for me as it appears down the side of the house for a while

Looking fwd to not having to tell Cartes Du Ciel that it's close but not quite on the money. Thanks for your input Ben

Steve