I cannot use the polar scope in my NEQ6 - it's not that I don't know how - I DO - it's the fact that where I view, seeing sigma octanis is like winning Gold Lotto. I will eventually move to the Dark Spot (I am your father Luke...), but for now I mut make do.
So, I have been going it the old fashioned way - compass, carpenters level, and a bubble level. Compass to orientate the mount to True South (mag south minus mag dec.) Bubble level to first level the mount (the NEQ6 has it built in - I used a seperate one in the HEQ5), then a carpenters inclination level to set the altitude to my latitude. On doing this, I get to usually within 30' - rarely has it ever gone over 1° (though tonight I stuffed something and it was 4°E out in az.) Close, but no cigar, though a 3 str alignment works wonders - though I am STILL getting star trails (unguided) if over 30" exposure.
So, is there ANY better way of aligning, considering I cannot see Sigma Octanis, a drift alignment is nigh on impossible thanks to Westerly arborial obstruction up to about 45° above horizon and excessive light pollution westerly, plus NO north view AT ALL (did I mention I have to move??? )
Short on getting an inertial reference system or something, is there ANY software or digital hardware that will ACCURATELY point celestial south? Something GPS driven? I want accuracy, but I am NOT getting it, and it is driving me insane!
To drift align you need to point the scope low in the east or west and straight up, so I don't see how obstruction to the north would hurt. Light pollution should also not be an issue, I can drift align from my place at twilight with barely any stars visible. I use my autoguider to watch the star for me, but you should be able to see something in a reticule even with lots of light polution.
I have no visibility west or east due to trees (arborial obstruction as I put it) - the gum trees west are up to about 45° elevation and the east is blocked by a street light, a damned European myrtle and usual horrendous skyglow thanks to "city" lights (I can barely even see Betelgeuse until it is 45° up or so)
Solar noon and a plumbline is your best Nth\Sth starting point. that gets you one pretty accurate alignment direction ( and is not subject to any error in magnetic Nth Pole measuring ).
Then I use my Android tablet with a free Inclinometer application to get pretty damn close to the right dec angle. Then refine by observation and drift alignment along the ecliptic line. Phones will work too but the tablet has a longer straight edge to be more accurate.
When I was setting up each night before the Ob I marked out three spots on the driveway where the tripod would sit. I also had a levelling strip made of a length of 2 x 4 shimmed to counter the drives slight downward slope. As long as I didn't move the mount head on the tripod I could carry it out, add the scope and be viewing within 15 minutes with reasonable accuracy.. The one meter long builders level was far more accurate in setting up the length of 2 x 4 than try to balance it on the mount head edges.
Heres a pic of my 'Driveway' setup. Might explain it better.
On doing this, I get to usually within 30' - rarely has it ever gone over 1°
just to clarify, are you talking here of goto error after 3 star alignment? If you are talking of PA error, how do you measure it?
though I am STILL getting star trails (unguided) if over 30" exposure.
that is actually pretty good unguided. stars will trail on longer exposures due to periodic error in the RA axis, which is going to be maybe 30 arc secs over the worm period of the mount - that will translate into maybe 60 pixels at that long a focal length, depending on your camera. Nothing to do with PA. A few options include a tuneup of the mount and maybe PEC, but the best way to fix this is by guided imaging and you should get OK results if the PA is within a degree. Your signature implies you do guided imaging - what results do you get?
Got that too (in the beta form some time back) I run it, do the adjustments, and really not much different.
again, how do measure how well the Synscan PA routine performs?
Have you googled or tried polar alignment using PHD. I have a similar issue with lack of E or W Or S horizon or North actually so I use slightly higher stars and keep tweaking till I am happy with nice round stars (guided) at five minutes.
I could never see Sigma Oct through the polar scope of my NEQ6 either, and i have dark rural skies.
So...I use the Alignmaster software for polar alignment. Basically gives you pairs of stars (like a two star alignment) - you just pick one of the pairs that is visible in your sky, the mount will slew to the first star, centre and click ok and it moves to the next star. Centre again and click ok, and the software will display the alignment error. It then moves the mount slightly, and you recentre the star using the AZ and ALT screws as instructed.
You dont need to have a view of the SCP to use the software, and there are instructions here on IIS for adding additional southern stars to the database (which otherwise is skewed to Nth Hem stars) so you have more star pairs to choose from.
After iterating 4 or 5 times through the star pairs, I will generally get my mount to less than 30 arcsecs of the SCP. Takes about 30mins max, but I have marked the pavers where i use the scope so that I can set it up as close as possible to the correct position from the start of my session. Doing this usually sets me to within a degree or so in AZ and 10 arcmins in ALT before i even start the alignment process.
(just remember to change the settings on EQMOD from "append on sync" to "dialog based" whilst using Alignmaster, otherwise it messes up the whole process, and you'll be left wondering why after 3 hours at the scope it's still not aligned properly - been there done that... - then remember to change it back once your finished the polar alignment... been there done that too!)
With limited vision myself at my place I find alignmaster not great. It is very good when I can see the stars, but my obstruction to the south hinders me. I would bet that the reason you have out of round stars is as stated earlier that you have differential flex.
You are imaging at 1800mm on a mount with high periodic error, I doubt you will get round stars with perfect polar alignment (guiding turned off). If you then turn guiding on and cannot get round stars it is due to differential flexture, which would be prominent because of your image scale. If I do a quick drift align and take a minute unguided exposure my stars will not be perfectly round (800mm focal length). But as soon as I start guiding the stars are perfect, and I have exposed to 20 minutes. With a relatively large steel tubed scope and a focal length of 1800mm I would have thought an OAG would work better, it certainly is better for me. Of course I have no experience at long focal length. (I imaging finding a guide star will be a pain)
Short on getting an inertial reference system or something, is there ANY software or digital hardware that will ACCURATELY point celestial south?
Align master after a few iterations will. And there are more than enough pairs of stars to choose from in the database. It's very simple to use and accurate enough.
I've tried a few methods including the phd drift align, alignmaster, but have settled on the CCD method described here http://www.observatory.digital-sf.co...nt_CCDv1-1.pdf
I haven't measured how close I am, but unguided exposures seem quite good.
one major reason for me to use this was balance.
you need to drift align using the main scope and if you're using the guide camera in a guide scope, then you need to remove it and fix it in the main scope which throws it out of balance.
so the CCD method works for me since I'm using the main CCD in the main scope and don't need to change anything.
Other two methods I'm to try are using PolarAlignMax that uses plate solving with Maxim and EQAlignmax. Not sure how good either are.
With Alignmaster, I have replaced the sterne.txt file but find that the star pairs are usually very low.
I use EQAlign to polar align my mount. It's basically a combination of drift aligning and Alignmaster. You pick a star near meridian and use a camera to watch drift in DEC. After about ten minutes, the software guides you as to how far you need to move the mount East or West. I generally do this twice and I get very little drift after ten minutes. I don't bother aligning in altitude because it generally doesn't change between sessions.
If you have to wait 10 minutes for dedicated software program's to help you drift align for each axis then don't bother with them. Get as close as you can using manual hairy eyeball methods and remember that auto guiding will deal with the rest.
Be pragmatic. Meridian and celestial pole for drift alignment, don't worry about being "exactly" 30 degrees, go higher of you need to but provided you can still get north/east stars you will be fine. You are autoguiding.....for tweaks, use the functions available in your preferred guiding software such as phd or whatever else exists.
)
- then remember to change it back once your finished the polar alignment... been there done that too!)
Sigma Octanis
