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polar alignment is way off??


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I have a question for anyone that uses a goto EQ mount. Mine is a Bresser exos2. So everything I've read is basically start by pointing the polar scope north. Then for me 45° is my latitude. Now after that I've read you look through the polar scope to get Polaris to be inside a small circle according to how some other stars appear. Anytime I've done this it's been way off. Like by 30° longitude off. Last night I set up scope to point true north with a compass. That happens to be about 33° longitude away from Polaris. When I went to object I was about 1-3° off longitude. So my question is... Is this normal? If so then my Polaris view scope seems worthless.

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Looking it up I suggest you do not use a compass. The difference between true North and magnetic North for Salem OR is just over 15 degrees. So if you aim it North by a compass you are aiming it about NNE as best I can tell. Whatever it is 15+ degrees wrong.

The "easy" way will be to level the mount fairly well, then set the Latiutude to 45 via the scale on the mount ( the mount has to be level for the scale to be meaningful), assuming the scale is correctly fixed, then rotate the mount and polar scope to get Polaris in, then adjust so polaris is at the correct poition on the reticule via the fine Alt+Az adjustment bolts.

As at the start the problem is a compass: http://www.magnetic-declination.com/#

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2 minutes ago, ronin said:

Looking it up I suggest you do not use a compass. The difference between true North and magnetic North for Salem OR is just over 15 degrees. So if you aim it North by a compass you are aiming it about NNE as best I can tell. Whatever it is 15+ degrees wrong.

That's a big variance! As you say, best to ignore a compass if that's the case and just visually point the scope at Polaris with the correct latitude set and it should appear within the polar scope allowing you to set it accurately

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Will also say that seeing where Salem OR is situated there is further North Vancouver Is and on the main highway North there is a big stretch where a compass flips completely and if you are driving North it indicates you are heading South. All caused by igneous rock deformation where the rocks were moved but they maintain their now incorrect magnetic field. Just thinking you could be in a similar area/experience owing to the rockies formation.

On a drive to salmon fish I spent too much time looking at the in-car compass. To "fix" it (once out the magnetic anomoly) you had to drive in a circle 3 times it was suggested.

Will say 15 degrees is one of the biggest "general" ones I have seen, when anyone has asked. By the way do not trust a mobile phone as they often use magnetics also, even my tablet with GPS uses the magnetic aspect. Which is annoying.

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Just point the body of the mount to Polaris by eye, adjust the altitude of the mount to roughly your latitude, then look through the polar scope and Polaris should be there, then centre Polaris (if you want a very rough and ready polar alignment, just put Polaris anywhere near the centre of the polar scope reticle. If you want a really tight alignment, you'll have to make sure the polar scope is perfectly aligned with the RA axis of your mount and then polar align (but this is advanced stuff).

 

Bresser EXOS2.png

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I find it much easier to identify Polaris while its still just light, it becomes very hard once it is completely dark and so easy to pick the wrong star. I have a DIY polarscope illuminator on my mount and often turn it up to make sure.

Alan

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Thanks. Yes, for some reason I felt pointing north is good so pointing TRUE NORTH must be really good. Haha. Now that spring is here in about a week I won't even have a view to Polaris as my neighbors tree is filling out. As soon as I find a good spot that has really good alignment I'll have to mark the legs on the ground. It's not often that I find a target. Even when I was using the Polar scope to align with Polaris in the past

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Yes, once you've got a suitable polar alignment, you will need to do a star alignement else you won't be able to GOTO anything. I'm sorry if I'm going over the basics which you know but others may be reading this:

- polar alignment allows you to track objects in the night sky,

- star alignment teaches the mount/telescope where things are in the night sky at that moment in time (that you do the star alignment); it then remembers this and the internal software will allow you to GOTO any target in the database.

 

Clearly the better your polar alignment, the better your tracking will be. The better your star alignment is [and potentially the more stars you do an alignment on] the better your GOTO accuracy will be.

 

There are very many caveats to the last sentence, but I won't go there for now.

 

James

 

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Thanks. I know sometimes I get into a rush since Oregon weather is often horrible when it comes to viewing the skies 10 months out of the year. Thus skipping crucial steps. Thanks for all the help 

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It's always worthwhile getting together with others at star parties and the like and getting direct help from them and picking up tips. The one thing which is worthwhile is to type out a flow diagram of your setup routine, like a check lick. Print it out and get it laminated, or just print several copies so when it gets damp by the end of the night it doesn't matter.

Have fun, it looks like a lovely mount, and keep asking the questions.

James

 

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Marking the position of your tripod legs and adding (additional) 'liquid paper' (Tippex) index marks on your mount after finding Polaris (and hence a successful Polar Align) can be helpful for the NEXT time when you CAN'T see Polaris.  But what if you are away from home, or have just laid (say) artificial grass that you don't want to mark with blobs of paint and/or stakes? I had the latter problem.

I devised a very simple triangular 'polar alignment jig' made from three pieces of wood to which I affixed three caster cups; plus a compass. I align the jig along the meridian using the compass; drop my tripod legs into the caster cups; adjust my latitude (I use a wedge) and invariably I am under a 2° PAE in each axis with Polaris in the FOV of my Finderscope. Even if I can't see it due to cloud, I know it is there! It's as easy as setting up the red balls on a snooker table.

I then do a EQNorth/EQAutoalign + Polar Align using a NexStar + HC; then do a StarSense Auto-align (e.g. on a Celestron mount with wedge; where I swap over HCs) and get fantastic results measured as a few minutes PAE. I use this 'dual HC' routine to get around a current 'bug' in the StarSense polar align routine. Provided wedge = yes in the StarSense HC (via Menu); its final auto-alignment works a treat on a prior polar aligned mount.  The PRIOR rough accuracy of using my jig means that the NexStar + HC routine then keeps my Cal stars within the FOV of my 9 x 50 RACI Finderscope making the initial (two star) EQNorth/auto-align step very easy. After that step, it is as easy as it comes, even with quite clumsy wedge adjustment.

Polaralignjig.JPG.5e363f1e61f5b730d576d7e32185f3a9.JPG

 

 

 

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So last night I had a clear night and decided to see how close I could get my mount aligned. I did the polar alignment then tried 3 star alignment, 2 of the 3 stars were behind trees, so I tried a 2 star alignment and the only 2 I could visual see was Spica and Vega. Well it wouldn't list Vega! Apparently that wasn't an option. So I used Spica and Arcturus. Both were fairly close in the eyepiece and easily centered for alignment. It did its beeps and said it was aligned. Cool. So I went to Jupiter and it went right to it. Then I went to m101 which I can't see but it went basically where it should be in the sky. Then I tried M51 which is not far from m101 on the opposite side of Alkaid. But it didn't go anywhere near that it slewed almost horizontal with the Horizon. I thought crap. I must have hit m31 as that is more likely where that might be. Nope I checked it 4 times. I went back to Jupiter dead on, Spica dead on, Alkaid dead on then back to M51 and it goes horizontal. I tried a 2 min exposure when I went back to M101 and have no idea if that was even dead on as nothing showed up in the image but stars. I'm really getting frustrated with this. I've changed the power cord for a brand new one from factory, a brand new battery in the hand controller. Ughhhh. So frustrating to have to spend 3 hrs just trying to find an object. I ended up just getting a few 2 shots of Jupiter and packed it up

17991765_10155730480017565_4530389011824303580_o.jpg

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As best I know the Bresser data came from the Meade mounts as does the ES, Vega is in Meade star data and as I didn't check first it is in the Synscan +Celestron data. I took a copy of Meade's from the Weasner site some time back. Not sure if there is a best month for Vega in Meades, there is in the Synscan (=July). Not 100% sure Vega is an alignment star as in the data they are marked with an "a" and I cannot locate that table, but I would seriously expect it to be, as it fits all the old MEade requirements of big bright and single on its own.

I am beginning to think that there is some incorrect data in there somewhere as what you describe makes little sense. The big question is which bit of data. I know on my 2 Meades I have at times given up, reset the whole thing and sat down and reentered it all over again. One of mine decided one night that it was no longer an Alt/Az mount but an Eq mount.

The "easy" wrong data is Timezone and DST, at a guess you are UTC-8 and DST = On.

My only suggestion is to write down all the data for your location, then Reset. Then reenter it all again taking care, too easy to repeat a problem.

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Hi Mercona

Spica and Arcturus aren't ideal alignment stars as they are quite close in RA, Vega would have been good but as you said it wasn't an option.

However, you managed to GoTo Jupiter, Spica, and Alkaid several times, so alignment was good enough for that southerly part of the sky.

So I think your time and location  settings are correct, and I can see no reason why it wouldn't GoTo M101 and M51, which are both very close to Alkaid.

What makes you think you didn't?

Both objects could be there in an eyepiece at the usual GoTo accuracy, but be just out of frame of your imager, depending on your imaging scale.

Also M101 was only just visible on my 5 minute exposures  on a F6.3 scope at ISO800, so 2 minutes may be insufficient to show it.

If your Bresser does have Meade data in it, then these charts of the alignment stars for each season should help:

http://www.weasner.com/etx/buyer-newuser-tips/starcharts.html

Good luck

Michael

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Sorry, just realised I posted this as a comment not a new thread.   I recently bought a second hand Skywatcher 150P on 3-2 mount.  Bought a new polarscope for it (the new pattern one) and have downloaded the appropriate app for my phone to use it with, but have had nothing but problems trying to set it up.  The main issue I think is my "heavy handedness" when trying to get the reticule set up.  If Im honest, Im not exactly sure what Im doing, I have replaced the polarcope in its entirety (there was already a bracket attached to the mount).  I contacted SW and they advised to remove the original bracket and replace with the new one, in addition to replacing the allen screws with the grub screws from the original.  I removed the OTA and weights, adjusted the mount so that it was at 0 degrees elevation and tried to use the corner of a roof of a row of houses behind my house as a "fixed point". Heres where the problems started.  Rotating the mount through 180 degrees threw it wildly out.  So I tried to adjust the corresponding screw to get it to about half way, then realised that everything had gone out of focus and the reticule had seemed to have "dropped".  Im not sure what to do or where to go from here.  It seems that I only have to adjust the grub screws a small amount and the reticule drops.  Is this a fault with the scope, its operator or maybe both.  Appologies if this is duplicated elsewhere, I tried a search, but all the links seem to be in relation to EQ5/6 mounts and synscan.  

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The thing that you need to remember with polar scopes, is that they need to be properly centered as well.  I'm not sure how to do this on a given mount, but it's worth looking up and doing it.   In addition, the position of polaris changes based on the hour angle. there are apps that can help determine this for you.

Once these two things are done right, it should help to get your fairly close in your polar alignment.

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If the Goto set-up criteria are anything like the ones on the Goto on my telescope, and I can see a guess that they might require similar data.  The OP might find the use of SynscanInit 2 app. on a mobile phone with GPS switched on useful to check that they have the correct location, date and time data entered into the Goto unit? 

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I put this app on my phone..thought it was really good and it showed the long/lat at the location...decided to change my handset as it was slightly different..first star was in totally different part of the sky...so as in all apps don't rely on in being 100% accurate

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3 hours ago, newbie alert said:

I put this app on my phone..thought it was really good and it showed the long/lat at the location...decided to change my handset as it was slightly different..first star was in totally different part of the sky...so as in all apps don't rely on in being 100% accurate

Perhaps all the various systems are different, but with mine I have to choose the location of the first star in the calibration process myself after setting the location, time & date etc. I wouldn't be in a position of letting it find the first star.  If I updated the location I'd then have to re-calibrate it myself and therefore locate my own first star.  I guess all the systems are different.  Also the relative position of the star you use would change from night to night, even hour to hour so I guess I'm a little baffled! LOL  It always seems to work with my location (you do need your GPS switched on, on the phone), and you can always double check the lat and long on Google maps.

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