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Old 03-01-2015, 11:30 PM
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FrankyT (Frank)
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Help With Polar Alignment For Astrophotography

Hello I have a 3 month old Skywatcher Neq6. I have the slightest most annoying problem with drift even after numerous polar alignments. I get star trails in my photographs after 30 seconds. I do not have auto guide set up but am expecting to at least get a 2 minute exposure with no star trails. I would have hoped this would be reasonable with all the money I have spent. Firstly I am in the southern hemisphere and do not use the polar scope. I line my mount true south and ensure the tripod is level in all directions. The bubble level on the mount is not reliable. I have ample power and have good steady supply. I end up doing the 3 star alignments followed by polar alignments and have 0.00.00 readings. However the drift still occurs and any exposures of more than 30 seconds star trails appear.

I have a X5 barlow on a 12.5 mm reticule eyepiece. After a few seconds you can see star beginning to drift ever slightly but enough to ruin the photographs.

As yet I have not tried the drift align as described on these threads and am embarrassed to say I do know if its right ascension or declination that's drifting or both. It started raining and I had to call it quits tonight. The software with the Neq6 has a polar alignment procedure but it or I am failing. PEC prevents star wobble but my error is worse than that. When you zoom in on a photo you see the trails.

I thought levelling, good power supply and repeated polar alignments would hone it in but it doesn't. I am using the exact time to the second and longitude and latitude from GPS in the set up of the synch scan.

I have been told to keep persevering but I seem to think there is an issue somewhere with the gear but cannot prove it.

Thank You In Advance
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Old 03-01-2015, 11:40 PM
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mswhin63 (Malcolm)
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I had been struggling with alignment for a while, but now i have finally settled with Drift Alignment as the method that provides me with the best accuracy. If it is possible for you to do it then have a go. I used PHD2 for drift alignment as it can pick the best stars for alignment based on my camera.
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Old 04-01-2015, 12:35 AM
alphanull25 (Niall)
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Hi Frank. I was very interested in your post as I am having very similar problems. I have a 8inch F5 reflector on a HEQ5 mount. I have got everything perfect, even the polar align function reports zero error. But as soon as I move to an area to photograph, the alignment is off and 30 seconds causes slight movement in the stars. Any longer than 30 seconds then forget it. This has been going on for 6 months. So I might try the drift alignment method, if the sky ever gets clear again
Niall
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Old 04-01-2015, 01:59 AM
raymo
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No one can help you without knowing what focal length scope you are using, and whether you are attempting prime focus work, or eyepiece
projection. At what stage are you using a 12.5 mm reticle EP? and why
the barlow? If your scope is around 1000mm F.L. with good P.A. you
should expect to get around 90-120 seconds without star trails.
raymo
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Old 04-01-2015, 03:24 AM
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jsmoraes (Jorge)
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This issue, polar alignment, is more complicated than you are thinking.

1) For astrophotography you must have high precision. Therefore the visual procedure for drift analyse isn't a good option. You need to use a camera. Webcam for example. You don't need to have beautiful images. You must have a star only as a dot spot. The best software to do polar alignment, for me, is EqAlign: eqalign.sourceforge.net/index-en.html

It tells you what and how much to adjust. It is interactive. It has some problem with freezing the camera image, but you can work well with it.

2) NEQ6 isn't a good mounting with respect to Periodic Error. No problem for visual observing, but for astrophotography it is terrible. The file PEC (Periodic Error Correrction) will not work fine with NEQ6, since the Periodic Error of this mounting isn't repetitive. You haven't identical senoidal alike shape with many cicles.

3) it is normal you get only 60 seconds and sometimes, due to position of gears, a bit more up to 2 minutes.

4) if the grease of the NEQ6 gears is very old, the Periodic Error will increase very much.

5) if there is some gap between the gears ... you can't get a stable performance.

Conclusion:
With NEQ6 you need a guinding camera system. And this is another problem, also.
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Old 04-01-2015, 03:48 AM
adman (Adam)
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Hi Frank!

Drift alignment is one of the best ways to get a decent polar alignment, but it does take a bit if practice. It is best done with a camera using something like PHD / PHD2 or backyardEOS or astrophotography tool (APT) as you can very quickly determine which way the star is drifting so you can make your correction. Have a google around and you will find some good resources.

I found it was useful to have a good mental picture of what you are doing at each stage of drift aligning - basically there are two imaginary lines that you are trying to line up. Imagine for a moment that your telescope is a giant laser, then imagine the arc it would describe in the sky as you rotate it around its RA axis. That is your first line. The second line is the actual track of a star, and the arc it describes as it moves from east to west.

The only adjustments you have at your disposal (assuming your mount is level) are azimuth (spinning your mount around a vertical axis) and elevation (the angle your RA axis makes with the horizontal). Then imagine how those two imaginary arcs would differ if you are misaligned in either azimuth or elevation.

To align your mount in elevation, point your scope to a star lowish in the east. If your are properly aligned in azimuth the arc your telescope would describe will be the same as the star. If your elevation is too high your telescope will start to point to the north of the star - so the star will appear to drift south. Conversely if your elevation is too low, the star will appear to drift north.

Then to align in azimuth, point your scope to a star on the celestial equator near the meridian :ie straight up and a bit to the north. If your mount is pointing slightly west of South, the star will drift south, if it is pointing slightly east of South, the star will drift north.

There is a good description on IIS (google basics of drift alignment) of this and some good youtube videos that help you to get the mental picture right - once you have that it all makes sense. Keep at it though it does get easier

Cheers
Adam
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Old 04-01-2015, 05:59 AM
glend (Glen)
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Frank there is nothing wrong with the NEQ6 being used for imaging. A good polar alignment and orienting to exactly true north helps alot. Try downloading the new version of the handset software as that has the polar alignment correction routine in it and that's a big help for correcting PA if your mount is setup each time you use it.

If your serious about imaging you will eventually wind up autoguiding the mount for long exposure accuracy. An autoguiding setup is not expensive and you save alot of time with messing around with drift alignment etc.

Autoguiding software is free (Metaguide and PHD2), you just need a guidescope and a guide camera with an ST4 port - all of which can be had for less than $500.

Once you can guide your mount things get much easier.
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Old 04-01-2015, 06:34 AM
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skysurfer
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For short exposures, this method suffices.

I foud out how to align your EQ mounted telescope without polar scope to the pole.

http://skysurfer.eu/eqmount.php

With this setup I can expose up till 4 minutes with a 85mm lens of a full frame camera (50mm equivalent on APS-C).

EDIT: For those who do have a polar scope: Last year I found out that when you center BQ Octantis (+6.9) you are rather accurate. That star is only 10' from the south pole. I did this and I got trail-free images of 4 minutes with prime focus of the Genesis (500mm).

Last edited by skysurfer; 04-01-2015 at 06:55 AM.
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Old 04-01-2015, 11:03 AM
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Somnium (Aidan)
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I have a NEQ6 and i do a drift alignment, as outlined in this video (starting at about 31 mins)
https://www.youtube.com/watch?v=zQB6UnrTEEM

i only do a 30 second drift because otherwise it would take a long time to align, but i have an autoguider so absolute precision is not as much of a priority. you may wish to do short exposures (15 -30 second) for a rough alignment and then long alignments to tweak, this will save you time. Without a guider i can usually get around 60 seconds (focal length of 1000) without star trails, 2 mins is probably pushing the limits of the NEQ6. I also only drift aligned the altitude once and then each night i just focus on the azimuth alignment. this saves a lot of time and provided your mount is level there is no reason why you would need to adjust the altitude every night.

with this process and some practice i have been able to get a a good polar alignment in about 5 - 10 mins
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