Arghh! Polar alignment and goto etc.

[duzzy]

Hi all,

My name is Jason and I have been fighting with my HEQ5 pro for nearly two months and I am getting a little bit frustrated.

I aim to image DSO's and have an SC1 modified Philips SPC900NC and K3CCDtools + CDC, EQMOD, registax etc.

The tripod wasn't stable enough so I have replaced that with a pillar. I have made a motor focuser.

All good apart from polar aligning the mount. I have trawled the net and read all I can on the subject.

The problem I have is that I can only view NE to SE and only to about 75 degrees above the horizon. Moving home to accomodate better viewing is not an option.

Last night I attempted to drift align on Mintaka as it is near 0 degrees dec and I as cannot point south I figured getting at least one axis aligned would be better than none. Eventually I managed to get the star to drift only slightly in dec.....but the mount now reads that I am at about 56 degrees latitude (I am actually at 51 15 16N). I have read that these latitude scales are not particularly accurate but could it really be that far out?

Another problem I have is that of goto accuracy. Am I correct in assuming that if my mount is accurately polar aligned then goto's should be fairly close? How about when I first start the mount and do a one star align?

After tweaking last night I parked the mount and started again. I told it I wanted to do a one star align on Mintaka. Not even close (unless I am expecting too much) in the finder scope I could see Anilam and Alnitak but had to slew quite a way to get Mintaka centred. Having aligned on that I told it to goto Betelguese. Once again I couldn't even see it in the finderscope it was that far off.

Obviously I have some major alignment problems but due to my location I am out of ideas as to what to do. One thing I have yet to try is to use my tripod down the end of my garden so I can see polaris behind my house and use the polar scope to align. Assuming I have levelled the tripod, when I then move the mount back onto the pillar (which is as level as I can get it, I checked again today) then even if E/W aligment is out N/S should be in?

Anyone have any other ideas?

Sorry for waffling on.

All the best,

J

[Breakintheclouds]

Another problem I have is that of goto accuracy. Am I correct in assuming that if my mount is accurately polar aligned then goto's should be fairly close? How about when I first start the mount and do a one star align?

You can't expect the first alignment goto to be particularly accurate, as that would not only require the mount to be perfectly level, perfectly polar aligned, and so on, but would also require the two axes to be EXACTLY in the park position when you set the mount up, which isn't likely to happen. I use three-star alignment and find that the first star is usually a few degrees out and then the second and third are really close.

After tweaking last night I parked the mount and started again. I told it I wanted to do a one star align on Mintaka. Not even close (unless I am expecting too much) in the finder scope I could see Anilam and Alnitak but had to slew quite a way to get Mintaka centred. Having aligned on that I told it to goto Betelguese. Once again I couldn't even see it in the finderscope it was that far off.

Can you use two- or three-star alignment? It should help considerably, and only takes another 30 seconds.

Good luck!

[steppenwolf]

Another problem I have is that of goto accuracy. Am I correct in assuming that if my mount is accurately polar aligned then goto's should be fairly close? How about when I first start the mount and do a one star align?

The key to this is to do something different with the first star alignment that ensures that the PARK position is accurate:-

The EQ6 mount does not have digital optical encoders so it does not have any feedback system to determine where it is pointing so it is necessary to start the session with the telescope in a known position called the ‘Park’ position.

This Park position is with the weights pointing downwards and the telescope pointing upwards but this is a purely subjective position although the mount assumes it to be an absolute position and makes its first slew on the basis that the mount was accurately parked at the start. Many mounts work on this basis and it is a reasonable method of controlling the mount but the accuracy of that first slew can be greatly improved by NOT making adjustments using the hand controller. Instead, I issue the slew command and when the mount stops moving, I carefully unlock the clutches on the RA and DEC axes and manually push the mount around until the alignment star is in the centre of the field of view and then I clamp the clutches to lock everything in place. At the end of the session when I issue the ‘Park’ command, the mount will park to exactly the correct position all ready for the next session. This means that I always find my alignment star at least somewhere on my sensor thus greatly speeding up the set-up procedure.

[SteveP]

Duzzy

Welcome to SGL

What are you using to align the scope? EQMOD or the Synta software?

Whichever software you use, I'd recommend the 3 star (or N Star) alignment rather than 1 star. It's much more accurate since you're using more points of reference. Your experience with Mintaka is to be expected unless you were really lucky with the initial positioning of the mount. After all, the mount doesn't really know where it is to begin with. Further alignments WILL improve things.

The altitude scale on the EQ5/EQ6 mounts is incredibly variable in its quality. I use an EQ6 and it's 3-4 degrees out so your experience is not unusual. But once you have it adjusted to the 'right' angle and you maintain the level of the mount during subsequent alignments, it shouldn't need much further adjustment if you then use drift aligning.

I tend to use drift alignment when i'm wanting a more accourate alignmnet. I found that Ian King's site has the best explanation including where to stand when looking through the diagonal. If you've not seen it previously, have a look here

- Ian King Imaging

Good luck

Steve

[duzzy]

Hi,

Thanks for the replies.

At present I am using the synta handset to do a one star align. I cannot use it to do a three star align as it wants to use the other stars that are outside my viewable area.

I have tried eqmod but as the mount is so off it is quite troublesome unless I am using the CCD and am at the computer (I did try getting my bluetooth PS3 handset to talk to eqmod as a handset (so I could use a low power eyepiece and zero in that way) but had no joy whatsoever.

Thanks for clearing up that the initial goto is never going to be that great and I understand about loosening the clutches and manually aligning the first star. If the next goto is out I am assuming I should then use the handset/eqmod to slew and correct?

I did start tweaking the E/W alignment sort of using that idea.

My original park was set using a spirit level on both axis. Then I told it to goto and unlocked the clutches and manually aligned. Then told it to park , shut down and saw how far off the original 90 degrees it parked to. Worked out which way it needed to move to roughly remove the error, unlocked the clutches and moved it. Restarted and said yes start from home. Rinse and repeat. I have a feeling that I got fairly close using that method but then I changed the tripod to a pillar and had to start again. Haven't tried the above again yet as I got hung up on attempting drift alignment.

Would a digital protractor help with setting the latitude? (would it be accurate enough?)

One more stupid question. If my polar alignment is out, when I first goto a target why unlock the clutches and adjust that way. Why cannot I not align using the mounts N/S and E/W adjusters?

Thanks for all the input. I knew it was going to be hard....possibly not this hard. Until I trust my mounts alignment imaging DSO's is going to be impossible. Fairly chuffed with the seperation of Almach I got though...

http://www.duzzys.demon.co.uk/images/almach.jpg

Cheers

J

[themos]

EQAlign can be used to help with polar alignment by the drift method. I did it last night and it worked quite well.

EQAlign Astronomical Suite

[Breakintheclouds]

I should say that I use the handset to correct the first star's alignment and haven't found any problems with doing so.

[SteveP]

Duzzy

You're not alone in not having 360 degree observing so welcome to the club!

If your HC is similar to mine on the EQ6, then you can cancel the alignment star which it suggests and select your own from a longer list of targets for the 3 star alignment. That ought to get you round your viewing difficulty

[Breakintheclouds]

It's times like this we SkyWatcher owners can envy Celestron's system where you just point the scope at three bright objects -- any three! -- and it works everything out itself.

[arad85]

It's times like this we SkyWatcher owners can envy Celestron's system where you just point the scope at three bright objects -- any three! -- and it works everything out itself.

Unfortunately, their all star alignment is only available on the alt/az mounts as far as I'm aware (my 6SE had it, the CG5-GT didn't...).

[duzzy]

The Celestron system sounds like bliss!

What's getting to me is that mine is a permanent set up. Once it's aligned I should be away. Last night I spent two hours trying things and to be honest I have no idea whether I have improved the situation or made it worse.

No doubt I will now have to wait ages for another clear night when I can start again!

Yellow pages list piano tuners but I cannot find any telescope tuners

Mind you if it was too easy I'd probably get bored.

J

[dark knight]

Hi and welcome to SGL Duzzy. K3ccd also has a drift align procedure which can be used. That said I spent from 9.00pm last night till 6.30am this morning trying to drift align and was still not happy with the results, in fact I gave up and kicked the dog...(well ok I didn't really kick the dog, he was snug indoors asleep). Drift alignment can be so frustrating especially if like me you get the RA and Dec mixed up, I was chasing my own tail for most the night... Whereabouts do you live, maybe there is someone close by who can help....

[Tim]

You may find it easier to use the goto to get your polar alignment correct.

You absolutely must have a level base/pier. I am not entirely certain of the technique, but a google for GOTO ploar aligning should get the result in the end.

Hope you get it sorted

[johnb]

Hi all,

The problem I have is that I can only view NE to SE and only to about 75 degrees above the horizon. Moving home to accomodate better viewing is not an option.

J

I have a similar problem due to trees and things, I level my mount point it North I have a line on the floor and have the elavation set to 51Deg and that seems to work ok with my with Goto after a 2 star alignment

Regards

John B

[dark knight]

Here's a link to a walk-through for K3ccd3

Using the K3CCDTools Drift Explorer for Drift Alignment - IceInSpace

I still struggled though...

[duzzy]

I was using the drift explorer in K3CCDtools last night.

I think I have worked out the directions correctly. (Note I only think so.....Rotating the CCD 90 degrees would change it all).

After two hours I had Sirius (Mintaka went too far West in the end, though it was still in the East if you see what I mean) hardly moving off the cross hairs for 5 mins or so.

So I assumed at least something must be aligned with something somewhere? Goto Betelguese.....way off. 11pm. Give up.

So (possible light dawning) maybe my polar alignment is improving as stars are not drifting as much (5 minutes is a great improvement on the 20 secs for the whole of the chip I started with), but that means nothing to my goto accuracy which I may be better setting in CDC with EQMOD and n-star alignment. Then if I park using EQMOD and don't fiddle with anything (always a temptation) when I next have a clear night and unpark my goto's may be close but I will still have to re-align anyway?

J

[duzzy]

Aha I thought, google 'goto polar alignment'.

All good and info I have not seen before but the instructions still want me to look at Polaris or near Polaris or Kochab. Or opposite sides of the sky and the zenith. Basically I can look East. Only.

Have I missed something or is goto polar aligning not going to work for me?

Cheers

J

(Basingstoke,Hampshire, by the football ground, with the massive spotlights. Seriously I doubt you could pick a better observing site )

[Tim]

Just because the drifting stops, or slows, that doesnt really mean that the mount actually knows where it is pointing.

Once you have the drifting under control, then re do the three star alignment, even if the stars are closeish, and you will be much nearer the mark.

[Tim]

just posted that same time as you

Whereabouts are you? sounds like a little hands on help wouldn't go amiss!

Do you have no southerly view at all?

[SteveP]

Jason

There is a little confusion creeping in here. Polar Alignment and 'Goto' or Star Alignment are different and useful for different purposes.

Let's deal with Polar Alignmnet first. Its purpose is to point the axis of your mount at the Celestial North Pole so that when it is TRACKING, the mount's axis is revolving in the same axis as the earth's movement relative to the stars. For visual purposes, PA does not have to be perfect. However, for AP purposes, it has to be as close to perfect as possible otherwise you will have star trailing on the images, ie the object is not being tracked perfectly. PA can be achieved by using software with a CCd or webcam, using a polar scope (so long as you can see Polaris!) or using drift alignment.

On the other hand, the function of Star Alignment is to improve the mount'sGoTo capability. It maps your mount's own assumed position onto its 'electronic' star map. To the extent that those two views are different (and they will inevitably be to some degree), your mount will then make corrections having gone through some form of Star Alignment. In simple terms, this is akin to a triangulation process whereby it has been told where 3, say, alignment stars are and from those points it can determine where the GoTo target is and slew accordingly. This is not dependent on an accurate PA. Software such as EQMOD when used with planetarium software can be further aligned (or Sync'd) thus creating more alignment points (as many as you want in practice) and therefore having more points from which to calculate subsequent GoTo's

HTH

Steve

[TheThing]

Andy's Shot Glass has a very good video tutorial for drift aligning. Although I have never needed to do it, I watched it so that I knew what people were talking about when that phrase came up! I understood it clearly first time.

I don't have a link for it at work - it's on the home PC - but I'm sure you can google it. He does a good video tutorial on collimation too.

[duzzy]

Hi all,

Steve thanks for that. I was assuming that polar alignment and goto accuracy were more closely entwined than they in fact are. I'm guessing if I pointed my polar scope east and told it to goto it would be way off however having it accurately aligned north does not mean my goto's will be spot on.

So I think my polar alignment is getting better (much less drift).

This is my viewing area (the doors slide open and are curved at the top)

http://www.duzzys.demon.co.uk/images/east.jpg

Cheers

J

Now I need to work in CDC and EQMOD to get my goto's more accurate.

Then goto somewhere and watch for drift.

[Starflyer]

As previously mentioned the altitude scale is not at all accurate on most of these mounts, you could be a mile out in altitude and not know it.

Can you setup (using your tripod) temporarily somewhere else where you can see Polaris? If so get the mount level, don't rely on the bubble level on the mount - it's as bad as the alt scale on my EQ6 Pro mount. Use a spirit level and get it as level as you can, then use the polar scope to polar align the mount.

This way when you go back to your usual area and setup (again with a spirit level if you aren't sure your pillar is dead level) you'll at least know that the altitude is close. WCS is the best software I've used for drift alignment and it's free to try for 30 days.

Cheers,

Ian

[Vega]

As a footnote to the polar alignment and GOTO alignment thing... If you're scope is poorly polar aligned and then you do a successful GOTO alignment.. you'll find the accuracey of the goto is still pretty good to start off with but then after a few minutes, the goto's false assumption of the sky begins to creep in. As the true sky moves over time, the goto becomes more and more inaccurate due to the mount being poorly polar aligned. Unfortunately they are two seperate things. Jobs which have to be done seperately if you want to use goto with any accuracy :-(

I do sympathise with the drift polar alignemnt procedure... its a real pain. Even though I have a clear view of polaris, I still used to polar align for photographic reasons (since then I started using guiding instead thanks goodness!).

Matt

[dark knight]

In K3ccd you do not have to worry about the orientation of the ccd camera, put a star on the ccd chip and select it, turn the mounts RA drive off, press the Angle button in k3ccd drift explorer, let the star drift across the screen for a sec or so but not off the screen and press the Angle button again, restart your RA drive, drift explorer then does a clever calculation and calibrates the RA and Dec directions, simples............

Unless of course your me, I was using the indoors pc so had to keep doing it, run outside to turn the drive off, run back inside to press Angle button, run back outside,,,,you get the picture, gave up at 6.30am and then spent an hour just using my eyes,,but all that running kept me warm at least....