Ever had one of those nights when everything was going so well, until...
I was trying to perfect my polar alignment on the pier mounted Vixen Atlux. Of course my house (two story) is to the East, blocking view lower than 30 degrees, and my observatory roof doesn't let me see straight up (whoopsie on my first design) - so that's just to make things more challenging.
I started at 9pm and finished at 4:30am. To cut a long story short had I finished at 12:30am I would have been a much happier boy with alot less work to do!
My starting point was a mount that is say within 1/2 a degree of perfectly level and I believe its aligned within 1/2 a degree off the SCP (according to MaxPoint). My goal was to do a 400 second unguided shot on a 9.25" SCT and get close to perfectly round stars - no trails whatsoever.
So at the beginning of the run I note that my Canon 400D when it snaps the moon as a 6" x 4" shot well the Moon almost completely fills the length-wise frame. S I estimate that 6" or 150 mm equates to 30 minutes of arc. My star trails for a 400 second (6 and 2/3 minute) shot (chosen randomly) started as about 5-6 mm. By just after midnight star trails where down to I estimate just under 1 mm - that would have been a perfect place to stop and start again fresh.
Instead I pushed it too far and too clumsily and managed after much effort to undo most of the good work I'd achieved! I gave up when I realised that hovering helicopter was actually Venus - time to go to bed!
My beginners mistake was of course to correct for movement in both Alt and Az (measured as movement from the Canon's central viewfinder focus point). Oh yes that's exactly what I did!
And of course as I started losing alignment I kept digging the hole deeper! I started with Archenar when it cleared the house - until it was almost vertical - not bad alignment. Then I continued with Sirius and managed to undo most of my good work.
Here's the question - do anyone else do daft things like this or is it only me? When your short circuit starts to fail do you tough it out or continue to dope it through until its clear your an idiot?
Well - I might try again tonight (the right way). Does anyone have a shot of what a long duration, unguided shot of a star on a long focal length tube looks like? Or can you mention what perfect alignment should look like?
I presume it will show no trials but maybe slightly blooby or football like stars if PEC isn't enabled. With PEC turned on I expect the stars will look closer to textbook points of light?
Here's four shots showing 1) size of the Moon in a frame and the rest are 400 second, unguided shots of Achernar 2) starting alignment 2) almost right alignment and 3) heading backwards oops!
PS
Given that 5 mm drift in a frame where the full 150 mm is about 30 arc minutes (width of the moon) it follows that 5 mm / 150 mm equals 1 / 30 of 30 arc minutes. So 1 mm of drift in my frame is 1 arc minute of drift. If I get 5 arc minutes drift in a 400 second shot this equates to 1 arc minute every 80 seconds - how far off the SCP am I - to any budding mathematicians?
PPS
Anyone local ever want to visit and help me really get this thing spot on - I'd be eternally grateful!
I've done things like align on wrong stars - so I printed out from Starry Night accurate finder scope field of views centred on every single Gemini alignment star (for both correct image and straight through finders) and had them bound into booklets....
I just drift align now - very painless once you work out basic directions.... from unaligned by a degree or two to getting within 5 minutes of arc now would only take me an hour or so.
I do have a burning question - how can an observatory not allow you to see straight up??
I can't easily see straight up because as a newbie I build a hyperbolically curved (to keep under councils 3 metre height rule) dome roof that only provides a viewing window from 15 degrees above the horizon to vertical. You really need to go 15 - 20 degrees past vertical to allow a German equatorial mount to see vertically, as the scope is of course not directly above the mount but in my case almost 30 - 35 cm away!
Yep we. or at least I have done things like you explained in your very informative story above.
But i just put it down to experience and, let it all go, and lay in bed and think how i will tackle the problem tomorrow.
It is surprising, but true, if you think about a situation long enough, the answer will all of a sudden hit you, and it will look so much easier to fix.
Can you photograph the area of CSP... if so try a time exposure with the scope in home pos. and move the mount until you get a circle... sounds funny but I have gone back to that when everything seems to go pear shaped...er yes pear shaped stars that is.
Some like the approach some say it is crazy but often it will point you in the right direction.. if not get it spot on...
Also I used to correct movement but it was the drive running slow.
and that will send you crazy.
Matt I would be happy to call by depending where you are in Sydney but no promises that I would have any greater chances... but I have done it heaps of times some good some bad.
alex
Now what Alex has said is true, I actually did that sort of thing when i was aligning the G11, and it really did work.
It was considered by some to be crazy, but it worked for me, and was one of the many strange ways i do things, but at the end of the day, it works, and is still working .
This is how i see the SCP if i take a 10 minute through the Tak in the home position, after a nights imaging and i put it to bed .
I spent three hours polar aligning with no sucess. Normally a 20 minute task after remounting the scope in the observatory. The next day I realised the reason for the remounting the scope was that it had returned after being in for repairs. I checked all the settings to find the scope was int ALT /AZ mode not Polar mode.
but it worked for me, and was one of the many strange ways i do things, but at the end of the day, it works, and is still working . 
