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Atlas GoTo Alignment question

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#1 rigel123

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Posted 17 March 2011 - 09:30 AM

I just started using my new Atlas EQ-G and love it. One question I have is when doing the 2 star alignment after I have it fairly well polar aligned, is it normal that on the first star that it picks that you have to slew it quite a bit to get the star lined up? Once I do that, the second star is always close to the cross hairs and the Go To seems to be fine, I just wondered if somehow I'm entering the time wrong when I am first setting up. I'm in Cincinnati so I enter Time Zone as -5, then the 24 hour time, and yes when it asks about daylight savings.

I'm use to my LS6 and now that I think about it, even when it is aligning itself when it looks for the first star it typically has to slew a bit after taking the first image even though it has built in GPS and knows it's location and time, North, tilt, etc.

Just wondered if this was inherent in all Go To mounts.

Warren

#2 EricJD

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Posted 17 March 2011 - 09:37 AM

I have the same thing happen with me. What I've noticed is that it seems to be very particular about the 'home' position. Seems the closer to the 'real' home position I get it, the closer it is on the first calibration star. It's not a big deal to me though.

#3 rigel123

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Posted 17 March 2011 - 11:54 AM

I have the same thing happen with me. What I've noticed is that it seems to be very particular about the 'home' position. Seems the closer to the 'real' home position I get it, the closer it is on the first calibration star. It's not a big deal to me though.


Thanks Eric, I was wondering if it was just me. I get the feeling it's inherent in most GoTo mounts that it gets to an approximation of where it thinks it should be and then you tell it where it actually is. It's always fine once you hit that second star. I guess otherwise we wouldn't have this step, would we!

Warren

#4 Skylook123

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Posted 17 March 2011 - 02:50 PM

No Warren, sorry to say, you're not unique, at least in this particular experience. What you are seeing is the result of true home and true level being part of true polar alignment getting you to the first star. All three need to be fairly tight onto perfection for a close approach to the first alignment star.

Here is my home grown algortihm after six years, four to 10 setups a month, each away from home at a public outreach.

1. Set up tripod. Level tripod with a bulls-eye level.

2. Add mount head. Add the counter weights to compress the looseness in the mount and tripod. Use something like an inclinometer on the top dovetail slot to set the latitude as close as possible. I got my inclinometer (a large protractor kind of thing used to measure wall angles or shelf angles) for $8 at Home Depot. Being level to start is essential here.

3. Add the OTA. Now level is even more important.
3a. With the full up assembly, ready to go (so that the CWs are in the right spot, this goes along with balancing the OTA), loosen the RA clutch and roll the assembly in RA until the CW shaft is level. I use the bulls-eye level on the front face of the mount, not the CW shaft which may have a slight shift. Lock the RA clutch. With the CW shaft level, set the RA setting circle to an easy number to remember like "6" or "0".
3b. With the mount locked in CW horizontal position, now loosen the DEC clutch and use the bulls-eye level to set the OTA parallel to the ground in DEC. Lock the DEC clutch. A bit of magic here; DEC ranges from +90 down to 0 and further to -90. Same as your latitude! So, now that you are CW level and OTA parallel to the ground, set your latitude into the DEC circle. Use the side of 0 that will allow the setting circle to read "0" when rolled back to North later on.

3c. Now, roll the mount in RA so that the CW shaft is down. Center it so the circle reads 6 hours in RA different from where levelled the CW shaft. I lock to "6" on level, "0" when CW down. Your value should be 6 different from level, whatever you used. Lock the RA clutch.

3d. Move the OTA to "0" on the DEC setting circle. If you used the right numbers when leveling, the OTA should be pointing straight North. Lock the DEC clutch. This is now your home position, with adjustment needed for polar alignment. Note - from installation of the mount head onto the tripod until this home position setup is complete usually runs about four minutes in my outreach setups.

OKAY, now need polar alignment to complete. I do an iterative alignment. This setup should be fairly good right now, but a few degrees of on polar alignment becomes very wide on stars near the celestial equator. So,here is my iterative alignment procedure.

4. Do a 1-star alignment to a star that is at least four hours different from Polaris (RA = about 2hr 46 min)to minimize human and system errors. Once aligned, Do a GOTO to Polaris. See how far off you are. Remove HALF of the error with the mount azimuth/latitude bolts. Not much more than half, because the trig functions and signs give multiple solutions, and if you try perfect on the first adjustment you will be chasing your tail all around Polaris.

5. Redo the 1-star alignment. Redo the GOTO Polaris (the iterative alignment). Should be much closer, maybe enough to get Polaris into the polar scope and put Polars onto the big circle at the clock position that the hand controller tells you it should be. Pay no attention to little circles and constellation pictures. Use the Hour Angle from the hand controller.

It takes me four or five more minutes to do the iterative polar alignment part after dark. IF I do the home position setup (the mount head will shift axes a bit in storage, so best to do this every time out if you move the mount), and IF I don't take out too much offset on the iterative movements, the doggone scope is bulletproof from here on out. Maximum I'm aware that it took me was total of 14 minutes because first, I aligned on the wrong star the first time for iterative alignment, so when the pointing at Polaris was huge I took out about 80 percent. When I aligned on the star on the hand controller, bang, one more iteration and home.

Good luck, lots more complicated to write than do, and this mount pays you back with tight GOTOs.

#5 rigel123

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Posted 17 March 2011 - 04:18 PM

Thanks Jim, that's a great description of what needs to be done. I have been level at the beginning (I use both a bubble leveler and the one on the mount) but the other iterations I can see should help it get even better. Typically after my two star alignment the object is in my FOV but towards the North. This should help on those really dim objects I hope to go for.

Thanks,
Warren

#6 EricJD

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Posted 18 March 2011 - 09:44 AM

This may help you, it has helped me tremendously. I stopped beginning my calibration steps from the home position entirely. Instead I aim the thing at a known star right off the bat and sync it there. The second calibration star is typically much closer to center than when I start from the home position.

#7 rigel123

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Posted 18 March 2011 - 12:41 PM

Thanks Eric. I think I have heard that from someone else on CN but on a different mount. I'll have to try that.

Warren

#8 rmollise

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Posted 18 March 2011 - 04:58 PM

This may help you, it has helped me tremendously. I stopped beginning my calibration steps from the home position entirely. Instead I aim the thing at a known star right off the bat and sync it there. The second calibration star is typically much closer to center than when I start from the home position.


The bottom line? It really doesn't matter how far off the scope is from the initial alignment star. What matters is that you center the correct star.

#9 rigel123

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Posted 18 March 2011 - 05:57 PM

[/quote]
The bottom line? It really doesn't matter how far off the scope is from the initial alignment star. What matters is that you center the correct star. [/quote]

Good point!! One of the things I really need to do is study up more on my star names!

Warren

#10 Phil Sherman

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Posted 18 March 2011 - 09:10 PM

I too, do quite a bit of outreach and use a setup procedure slightly different from Jim's. Most of our star parties start before dark so Polaris isn't available for polar alignment.

When I setup the scope; the legs are set on anti-vibration pads. This avoids the tripod's leveling changing as the mount is loaded up with equipment. The tripod's basic North alignment is done using a compass, while standing 3-5' behind the tripod.

Once everything is attached to the mount; I do a goto to the first object to be viewed; usually a planet or the moon, unlock the clutches, push the scope to the object and relock the clutches.

Once it's dark enough to see Polaris; I park the mount, power it down, power it up; then use the Polaris hour angle information from the hand controller to do a quick polar alignment using the polar scope. I return the scope to the home position using the setting circles then do a single star alignment. Instead of positioning the star using the directional buttons; I again use the loose clutch technique to center the star then accept the alignment.

This technique gives me gotos that almost always place all objects in the FOV of my finder - good enough for star parties.

I haven't tried Jim's technique but I do wonder what he does when Polaris is below he NCP. On my Atlas mount; there's at least 3 months of the year where a goto Polaris would smack the scope into the tripod.

Phil

#11 Skylook123

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Posted 18 March 2011 - 11:27 PM

Never had a problem, Phil, probably because our school star party season ends in early May, and the SCT goes away until Fall.

Early in my experience with the Atlas, I went through a succession of compasses that were flat out bad. I never could seem to get Polaris into the finder from a cold start. When using the mount for satellite tracking I found I needed precise alignment, so I started playing around with starting from a good home position, and since I was using the mount for school adventures I needed a good polar alignment to hold objects in the FOV.

Nice luxury to be able to set up before sundown. Most of our events are scheduled so setup starts at sundown, and the "customers" are standing around tapping their feet waiting for us to rock and roll. I used to cut corners excessively, and had awful GOTOs. Now that I frankly overkill on the setup, I can use a 9mm Nagler for nearly 300X on the galaxy candy, and nail them constantly within 5 arcminutes. BUT, the setup does not REALLY need to be as intricate as I do it. But it's like the story of the police officer seeing the gentleman in Times Square, tearing newspapers in shreds and scattering the debris about. When the officer asks the gentleman what in the world he is doing, he says "Keeping the tigers away." "No tigers in Times Square!" says the officer. "See, it works!" When I had the bad luck with compasses for over a year, I was so frustrated on the setups that I started the uber-precision process. It worked. But down here in Tucson we have the Mexican Monsoon that brings thunderstorms nearly every day from early June through to September, so Polaris is never down low when I use the scope.

Best setup procedure is like the best scope. What ever works. For me, level, home position set, and iterative polar to start are my shredded newspapers. Totally Off Topic, noting your location, I grew up between W.45th and W.48 off Detroit Ave., moved to Brunswick, went to Cleveland State its first two years (1965-67), and my wife is from Willowick. Small world.

Back on topic, I hope everyone with an Atlas or EQ6 or NEQ6 tries different approaches. No one right answer, just whatever works. I've heard recently about the growing subculture around the first goto (or 1-star alignment) and unlock the clutches method. Sounds much easier, never tried it, just might some day. Me, I can't ever seem to get Polars into the polar scope at the start. So, as I said, I shred my newspapers and the tigers seem to stay away.

#12 rmollise

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Posted 19 March 2011 - 06:52 AM

I just started using my new Atlas EQ-G and love it. One question I have is when doing the 2 star alignment after I have it fairly well polar aligned, is it normal that on the first star that it picks that you have to slew it quite a bit


What is "quite a bit"? A technical term? :lol:

Seriously, what matters as I said elsewhere in the thread is that you center your alignment stars correctly and carefully.

What affects how close the scope comes to the alignment stars? Correct time/date/time-zone/DST entries. And polar alignment.

What's more important to most people is the final quality of the alignment. With this mount, the key to that is, in addition to carefully centering the correct stars, that you pick good stars. This mount is fairly touchy in this regard. And don't just accept the first two stars the HC presents. Some mounts offer alignment star candidates in order of how acceptable they are. Not the SynScan. It just gives you a list of possible alignment stars, it is up to you to choose good ones.

Stars should be away from the horizon, widely separated in azimuth and _separated in RA_. I had fairly ho-hum alignments with the Atlas until I figured out (by reading the cotton picking manual) that the first two stars needed to be separated in RA by several hours. Observing that allows my mount, after a three star alignment, to routinely place anything I want from horizon to horizon somewhere in the field.

#13 rigel123

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Posted 20 March 2011 - 04:39 PM

Hey Uncle Rod, I guess I should have said originally I was probably off by at least 15 degrees. Having said that I took some time last night and polar aligned, picked a star and aligned to that, then went back to polaris and corrected as discussed previously. Then I did a 3 star alignment and the first star, Sirius was about a degree off. After that, the next two stars were almost on the cross hairs and after that everything I slewed to was dead center of my FOV.

Thanks for all the suggestions!

Warren






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