Polar Alignment

[Zuts]

Hi

I finally got my wedge set up and my reticle arrived so i tried to do a drift align in my back yard. This is difficult as i cant see the SCP and there are trees everywhere. Anyway after 5 hours i was absolutely nowhere and getting very very frustrated. Then i found this link http://www.aussiepeople.com.au/ASIGNobservatory/driftalignment.aspx and followed the drift alignment procedure for RA (but with tracking on) and in 5 minutes had a star moving along the horizontal reticle with no up or down movent for at least 15 minutes. It was not properly aligned in DEC as there was still some slow horizontal movement in the reticle.

Anyway i was so excited and since it was nearly 3am i decided what the hey, lets take some photos even though the DEC is a bit off. I have a meade ed 80 piggybacked on a nexstar 11 gps and a eos 300d. Usually if i image through the ed 80 i get star trails in about 45 seconds. This time i got nearly 4 minutes with minimum trailing. I cant wait until the next clear night to do a full drift align and see what happens.

For any beginner out there like me struggling with drift align the above drift align article is fantastic and actually seems to make sense for me. It will still take me ages to hone my technique but at least i have made a start.

I have attached 3 images. All are 4 minute exposures at prime focus F6. The first is without a filter and shows how bad the light is in Glebe (3km from Sydney GPO). The second is the same star but taken with an Orion broadband filter and the last is the first image run through photoshop.

I have heaps of questions but am insanely happy that i finally managed even a RA align.

Man, where are those clear skies...

[leon]

Zuts, you have done well, I to had troubles getting all aligned and stuff like that, but once i learned and mastered the art it is the only way to go.
Keep up the good work and of coarse you realise now that you are
hooked. :D

Great effort, and I'm glad you are now insanely happy. ;)

Leon :thumbsup:

[montewilson]

Hmmm - that site seems quite good. Don't forget there are probably some software/camera tools you can use to help with polar aligning. Being a drifter is cool but these days computers make it so much easier that you may be punishing yourself unecessarily. That said you should know how it is done to better evaluate the new tools on the market.

Its a bit like when I was a kid and my Mum wouldn't buy me a digital watch until I could read an analogue one. ;)

I'm in Sydney and happy to give advice where I can. I've been doing it for about 15 years. PM me if you need anything.

[iceman]

Great work Zuts.

There's also a great drift alignment / polar alignment article by Geoff Smith, here on IceInSpace (http://www.iceinspace.com.au/index.php?id=63,405,0,0,1,0).

I've found that trying a few different techniques and adapting to what suits you, works best.

[Zuts]

Hi All,

A bit dissapointing. I managed to get it sort of aligned, enough to do a 3 minute exposure but it took me hours and hours. The next night i tried again and thought it was polar aligned but when i turned on tracking it just wasnt. I guess I have to rethink.

Here is my procedure, are there any glring problems with it?

Initial
(1) Get fork arms pointing roughly south at roughly 34 degrees.
Azimuth
(2) point scope at intersection of meridian and equator. OTA at right angles to fork, fork arms horizontal.
(3) Align reticle so left/right/up/down on controller matches reticle lines.
(4) ensure have enough play on the wedge. By hand move wedge all the way left and then then all the way right. At each end ensure that star moves a different direction. Up at one end, down at the other. Then center the wedge.
(5) turn off tracking so i can pick up drift quicker.
(6) Find any star in the reticle within a few degrees of the meridian/equator intersection.
(6) watch for up/down drift and use the azimuth wedge controls to adjust accordingly until the star does not drift up or down any more. As the star drifts from one side to the other use hand control to move it back to the other edge. If there is no up or down drift for at least 10 times accross the FOV of the reticle then assume polar aligned in azimuth.
Declination
(7) with the ota aligned on the equator, rotate towards the east to about 20 degrees above the horizon. This is difficult as there is a big tree so i am probably 5 or 6 degrees off the equator.
(8) repeat step (3)
(9) find a star in the reticle within a few degrees and repeat step (6) with the declination wedge controls.

Finally repeat all the above for both axes to fine tune.

When in Azimuth the wedge/tripod bolts are loosened but when i do dec i tighten everything up.

Anyway i did all the above and then turned on tracking and did a two star align and i was nowhere near polar aligned as i got star trails after about a minute.

So i am very confused. Maybe doing the 2 star align (which is all the hand controler allows) which has the scope pointing at very funny directions caused the wedge bolts to loosen, i dont know but i guess i will try again.

[bloodhound31]

Hi Zuts, Is your Celestron balanced with a counterweight? If you have that heavy ED80 on top. alignment will throw off depending on the position of your scope. The fork arms will flex unevenly with the extra weight if it is not balanced.

If you dont have a counterweight, you can make one yourself if you are handy with a few basic tools.

There is one example here....
http://www.aussiepeople.com.au/asignobservatory/CounterweightBar.aspx

Baz.

[Zuts]

Hi Baz,

Thanks for the advice.

I dont have a counterweight so maybe i should get one. I have two dovetail bars so can easily mount one.

The problem is I went from one night getting 3 minutes and was very happy with minimal trailing. The next night i had it aligned (i thought) far more accurately in both axes but when i actually used it; it wasnt!

I guess if i persevere ......

In declination i have to be about 5 degrees away from the equator and probably about 30 degrees above the eastern horizon when i drift align, because of trees, the west is totally blocked. Is this a problem?

[montewilson]

Don't forget you don't point the scope at the magnetic pole but at the true pole which in Sydney is at about 348 deg. This will help you a get a lot closer before you get serious with drifting.

I do this with my mount and sigma octans is always in the field of my polar scope.

Don't forget I am in Sydney and happy to help. PM me if you want to and don't give up.

[Zuts]

Thanks Monte, being able to pm a knowledgeable bloke is great.

I did roughly align with true Nth and am sure I was Polar Aligned until i moved the scope. Drifting in Azimuth and Dec showed no up down movement.

One problem is the wedge I have does not fit the tripod with the supplied bolts. If i use the supplied bolts and holes the wedge controls are unuseable, so i use the other set of 3 holes on the tripod and got some wing nuts. I have talked to celestron Australia and they say this is a known problem and that inserts are available so that the supplied bolts can be used in the other set of holes.

Any other Nexstar wedge owners with this problem?

I am also thinking of getting an EQ6 and then selling my Nexstar and buying just a C11 OTA.

How do you think an EQ6 would go with

C11 OTA as guidescope
Meade ED80 for imaging
EOS 300D
2kg of other stuff, reticle, telrad, losmandy dovetail

Would it be stable enough for imaging?

Anyones help is greatly appreciated

Thanks Paul

[Doug]

Hi Zuts, an EQ6 should handle an 11"ota, but wait off for a little while yet. It is true what Baz said about balance, though my experience with a Meade 12" classic (fork mount) is that balance effects tracking 'big time', but has little effect on actual goto. This is because even if the load on the mount varies and requires more pulses to get where it is going, they will be supplied. The mount does not only calculate how many pulses to send to the motors to slew a given distance, it also looks at the shaft encoder outputs. The shaft encoders only report actual motion, not guesstimated motion based on theory( if you follow my drift) so as long as balance is not excessdively out, any balance issues are mostly eliminated in a slew (goto) operation. Tracking is a different issue altogether; Even auto-guiding will not cure a poorly balanced setup. When Goto fails, it is almost allways due to incorrect setup.

Doug

[montewilson]

The EQ6 is pretty good value middle of the road mount. I don't have one but they seem to have a good reputation. I know Mike (IIS name Sculptor) has a set up almost exactly like you are describing and he is getting pleasing results.

I am fairly sure you will get superior results with a GE mount over a fork. Unless a fork has been custom made for AP work it will rarely have the rigidity or performance required.

[Doug]

I suppose selling off a large dia fork mounted SCT in favour of buying an EQ mount and an SCT OTA would only leave one a few thousand dollars out of Pocket?

[Zuts]

Hi Doug,

I am hoping to be able to nearly swap my fork nexstar 11 for a new C11 OTA if i sell. Then i have a few bits and pieces, like a JMI case and a wedge. Also I think I can get a deal on a EQ6 with goto, new for around 1300.

So I am seriously considering it.

[Zuts]

Thats what I am hoping Monte, maybe I should PM sculptor and ask him a few questions.

I really like visual as well. Does anyone think I would be making a big mistake swapping a nexstar 11 fork, for a C11 OTA and EQ6 goto for visual. The nexstar is very simple to set up for visual, if a bit bulky.

[Doug]

Zuts, if you can do a deal you are happy with, go for it. I have an EQ6 and am very happy with it. It gives good performance for imaging and therefore obviously it is a good platform for observational Astronomy, and I doubt that the Nexstar would out perform the polar aligned EQ6, BUT.................
The EQ6 or any other GE mount is not easier to set up than the Fork.
For observational work, the Altaz mounted Nexstar has it all over any portable GE mount. For Imaging, the GE mount is probably overall better, however there is one drawback that is not an issue with the fork mount and that is 'meridian flip' this means that if you are imaging an object that will cross the meridian during your imaging session and you are using a GE mount, your scope will need to invert, you will need to re center the image and guiding, the images you will want to stack will need to be inverted, and in realignment, you might loose a little more of the fov that you would wish. errors in polar alignment will also (I think) result in a reversal of any field rotation from pre meridian to post meridian exposures. Sounds like I'm dead against it doesn't it?...not really, it is just something to keep in mind...nothing comes without a price.
On the other hand, fork mounts are not as rigid and tend to flex, also though they do not suffer from 'meridian flip' like the GE, as they cross the meridian, the fork balance alters causing RA backlash issues for your guiding/tracking enjoyment....nothing comes without a price.
It is possible to take excellent images using a fork mount. Usually as people progress with their imaging skills, they seek out better and better equipment, and this invariably means a good sturdy GE mount. Frankly, unless you can do a really good deal on a swap/upgrade, I think you would be better off waiting till you have more experience. Then you can make a more informed decision.
Just remember that Polar alignment is just as difficult/easy with either mount. Sure some would argue that the GE with a polar scope is so much easier. But for you and I who can not see the SCP, a polar scope is a waisted resource.

hope this helps,
Doug

[Zuts]

Thanks Doug,

Very sound advice again, you have been a big help as always and i didnt know about meridian flip. Us fork mounted guys dont get meridian flip but sometimes we can get meridian flop, good old sct's :) .

I agree about my lack of experience; and know i should persevere but depending on the deal i may still get the EQ6. One slight issue with the Nexstar is that it is not really a grab and go. The EQ6 is not that light but i would not be afraid of dropping it like I am afraid of dropping my Nexstar when it is hanging off the wedge.

To keep on using the wedge i really need to get those sleeves i mentioned as otherwise i think there is too much movement when slewing the scope, as i need to use the alternate bolt holes.

The EQ6 would be more than adequate for my meade ed80 and maybe i can pick up a small cheap scope for guiding.

Visually i am very happy with my nexstar, though not with Glebe skyglow. How is Cambeltown skyglow where you are?

I have another polar alignment question :) . When i drift align my current setup it is via the Nexstar and a meade 9mm reticle. I am getting about 300 by through the reticle so when i can locate a star it is easy to pick up any drift quickly. If I try and drift align through the meade ed80 for short unguided exposures on the EQ6 will it be practicable since the meade has a FL of only 480 mm and so my reticle gives only about 60 by. Is this enough to pick up drift reasonable quickly or will i need to barlow the reticle?

Paul

[Doug]

G'day Paul, I can certainly identify with the fear of dropping large scopes. I have as I'd previously mentioned, a Meade 12" classic. It is too heavy and the lift points are way off the C of G which makes thing worse. The EQ6 is comparatively light and even with an 11" OTA, the carrying around weight is split up so that is a big plus.
If you are going to drift align using an EP, you would be well advised to obtain a good barlow or powermate This is so regardless of which scope you are using.
Another way you probably should consider would be to put the money that you would use on a guide scope and barlow/powermate into a webcam and
'Lumicon easyguider'; why?
With the Webcam you can:
image moon and planets better than with the 300D
Use it to drift align either the 11" or the ED80 much more efficiently that using a reticule EP.
Used with the Lumicon Easy Guider* you can auto-guide the ED 80 or the 11"
*note that the Easyguider comes as suitable for either SCT or Newtonian/Refractor scopes, though the later should fit into a visual back. The Sct model would not be any good for a refractor. Also you would need to get a 2" model not the 1.25" one to accommodate the T adaptor for your Canon 300D.
On the matter of drift aligning, no matter how much money is thrown into a mount, guiding will still be essential for long exposure imaging. The EQ6, (mine at least) has too much PE for imaging. Even with Pec training which can easily be lost with the EQ6, long exposures are merely wishIcoulds. Auto-guiding is a must.

The attached image is a single 15min auto-guided exposure using the EQ6 and the setup I have outlined above.
Without auto-guiding, even though my EQ6 is pier mounted and very well drift aligned this image result would be an impossibility. This series of images were ruined B.T.W. by light pollution. I would have been better off using shorter exposures + LP filter, but it does illustrate what can be achieved using an EQ6 mount.


Light pollution here in smoggy downtown C'town is bad, probably not much better than Glebe, depending on exact location. I have some annoying Sodium lights and not too far away a sports field that can really make seeing the night sky a challenge....but you learn to cope.
cheers,
Doug

[Zuts]

Hi Doug,

A 12 inch Meade, how come you sold it? I was thinking of getting that or a C11 to put on the EQ6 mount. Did you have the Meade on your EQ6 and if so was there any room to spare for a guidescope and camera? Man it must have been a lovely scope and given you some stunning views.

I was asking about the barlow for the Meade ED80. The reticle i have gives me over 300 mag on the Nexstar and already the image is very dark. On the ED 80 I can use my 2 by Powermate but even that will only give me around 90 mag which may make it tough to drift align. Maybe I need a 3 by barlow?

I did consider getting a Giant easyguider and actually ordered one from OPT corp. I didnt get it in the end because I decided the expense was too great. Around 500 AUD including postage. Rather than spend that on a guider I got the Meade ED80 and a reticle which I felt was far better value as i can image through the ED80. Bloody hell if i had the money I would have got the lot.

I think that image is great. I wish I could get my stars like that. Its discouraging but when you see what is possible from photos like yours and others on this forum it makes you want to try and try again.

I am interested that you took that image from light polluted skies. If you look down the bottom of this post you can see some of my images. The first shows how light polluted Glebe skies are. The second is taken using an Orion skyglow filter. If you look carefully around the bright star you will see a diffuse ring of light. I cant imagine what causes this but guess it is something to do with the filter. All my bright star images have this ring. When you image from Cambeltown do you use a filter and if so do you get this strange diffuse ring around bright stars?

Anyway, enjoying chatting with you m8 and clear skies.

[Doug]

Paul, I still have the 12". It is not in use at present because at the moment it is too difficult to manage ...I'm waiting on a total knee replacement and in the meantime putting up with some rather severe osteo-arthritis. So much for the sob story; I did have it mounted inside my dome, on its tripod and wedge. Polar aligned also without being able to see the SCP, that is why I'm reasonably confident the Nexstar will align ok by my method as well.
I did not mean the 'Giant easyguider', there are others that are about $300, they are an off axis guider with the ability to move the guide camera around a bit to enable finding a decent guide star.
I don't use filters, and my 350D is un-modded. I did/do have some 1 1/4 filtewrs that I could use with the Meade DSI, but I have given up trying to image with that thing, and the filters are somewhat undersize for use with the 350D.
I think you had an upload problem with those images.
Light polution can be a problem Paul, the challenge is to overcome it. attached image is a stack of 12 frames each one 15 mins or for a total of 3 hours. It was as I said a waist of time, but it served a purpose. The image has been streched and shows some of the nebulosity of the reagion, but mostly washed out by light polution.
well I'm off to brave the cold and see if I can snap a galixy of stars.
cheers,
Doug

[richard omeara]

i have a eq6 and having trouble finding south pole.i am in perth city.is their a easier method?

[iceman]

Hi Richard, :welcome: to IceInSpace!

Get yourself a digital compass. I can't see the SCP from my location either, but using a compass with the magnetic deviation built in, just align the mount accurately as possible and then drift align for the ultimate accuracy.

[Zuts]

Lol, it is funny to see an old thread woken up. When I read this and look at my questions .........

For anybody new reading this, just perservere like me and in the end drift alignment will be no big mystery, after a few months like me you will be able to do it and then you can look over all your old threads at your questions and have a good laugh :)

Paul