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New iEQ45 owner not happy with Goto Accuracy

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#1 shakafell

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Posted 30 October 2012 - 09:32 PM

Hello. I am basically looking for any tips that can give me better Goto accuracy on my iEQ45 mount.

So let me give you the whole background. Currently I am using a Samsung SCB2000 camera for observing and I am upgrading from my first mount which was a Nexstar 8SE. I found that it can be finicky but on the best nights I get good gotos to multiple objects even without doing precise gotos. And other times it is an exercise in frustration.

So I bought the iEQ45 since I want to eventually get into more serious imaging and naturally I assumed it would give me better results but so far it has just been frustrating. I am using it with the same C8 scope and Samsung camera with a 0.5x focal reducer so its running at f/5. This gives me an FOV of about 25 arc minutes.

I use Alignmaster to do my polar aligning and I end with up an error of only 1 or 2 arc minutes in each direction which I think should be more than sufficient. The mount is perfectly level and balanced as well as can be. And I have all of my location and time zone settings correct.

Due to light pollution and buildings I stay strictly on the east side of the Meridian which simplifies things.

So tonight for example I used Alignmaster on Mirfak and Caph to dial in the polar alignment. I then used the hand controller to do a two star alignment on Caph and Enif and got an error of 2' altitude and 1' azimuth. I slewed to M15 and it was just slightly top left on my camera. Very happy with the result. Then I slewed to M2 and only half of it was showing at the bottom of the screen. Still decent result. Then I slewed to M30 and it was completely off the screen. So I had to go hunting around to find it which is not easy with the camera. M15 is right next to Enif and M2 and M30 are close by as well so I would have expecting accurate gotos in this part of the sky at least.

I have tried synching on nearby stars and on every object I goto but that doesn't seem to help. I also read that synching will erase the two-star alignment so I've tried it without synching too.

So is this simply the kind of result I can expect or is there anything I can do? Thanks.

#2 Stew57

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Posted 30 October 2012 - 10:08 PM

When the mount is acting up is a slew back to an alighnment stare accurate?

#3 Mike Clemens

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Posted 30 October 2012 - 10:10 PM

> is there anything I can do

It doesn't solve your actual issue, but you can bypass it completely by doing plate solves and syncs. (Providing you have a computer involved in your imaging.)

#4 Midnight Dan

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Posted 30 October 2012 - 10:17 PM

Hi shakafell:

It is odd that tow targets so close to M2 and M30 would be off. I wonder if the iEQ45's coordinates for some targets are wrong. Have you tried using software such as Stellarium to drive the mount's gotos?

-Dan

#5 Astronewb

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Posted 30 October 2012 - 10:28 PM

Perhaps Alignmaster is affecting the polar offset routine? I'm assuming you're moving the mount in az and elevation to center on Alignmaster stars? Try just using the excellent polar scope, with a well leveled mount, without excess cone error...it will get you to under 10 arc minutes out of the gate. Using the 2 star aligns to dial it in to 1 arc minute or less will always result in perfect go-to's (on my mount). And, it should not take you more than 2 or 3 iterations of the routine to get to a polar offset of '00-00'.

Just a thought...I've never used Alignmaster, never had to with the iEQ45.

One more thing, check iOptrons support page and make sure you have the latest firmware loaded up, there have been some changes.

Cheers,

Paul

#6 Phillip Easton

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Posted 31 October 2012 - 07:07 AM

Are you doing a 1 star alignment before using Alignmaster? My feeling is that doing this causes problems as you want to do the Alignmaster process without any electronic correction by the mount.

When you do the two star alignment does the error it gives more or less agree with the error you get with an alignmaster check (applying no corrections to alt or azi)?

Is there a lot of play in your axes? I have struggled with GOTO's like you have. My Goto's will put the star in the finder scope but sometimes not on the camera. I even use Alignmaster to try an make sure I am getting the best alignment. To me there seem to be excessive play in my axes. So GOTO's work in a narrow portion of the sky but when slew to another portion of the sky this changes the orientation and the play in the axes causes the GOTO's to be off. This is one reason I want to try Paul's belt tensioner on both the RA and Dec axes.

So I always slew to a bright star near my DSO and sync to it. Doing that I can get the DSO pretty close to center. But if I go to another target far away I have to sync on another star.

Cheers!
Phillip

#7 Astronewb

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Posted 31 October 2012 - 07:27 AM

I have some more questions too. The manual clearly states that performing One Star and Two Star alignments will improve goto accuracy. But someone told me that the mount doesn't actually do anything with the Alignment information other than display the error for you, and that the accuracy is determined solely by the polar align. Is this true?

Also should I be synching on nearby stars before I goto a faint object? And then should I be synching on the object as well? Does synching replace the alignment information, and if so is that desirable or not?


A accurate initial polar alignment is critical, like the foundation of a house.

Some suggestions, make sure your polar scope is accurately adjusted and aligned. There are several files on the iOptron Yahoo group explaining and illustrating how to do this.

Using appropriate levels, square the mount in both axises. To minimize cone error in RA, set up your mount with the counterweight shaft aligned with the front (north) facing leg..use a plumb bob off the shaft perfectly intersecting the front leg and mark your RA basic setting. I use a small white tag on the RA joint, put a fine line on it and cut it at the joint with a razor knife, do the same with an OTA in the saddle and mark the DEC joint the same way. Now you have a 'base' repeatable setting.

When performing a PA, to double check..center Polaris in the crosshairs in the polar scope, with an EP in the OTA, Polaris should be centered in the EP also. It may be off vertically, but you can't do anything about that unless your OTA plate has cone error adjusting screws. If it's off significantly horizontally in the EP, adjust the DEC manually and remark the joint.

Now you can adjust Polaris using the handcontroller position indicator to the correct position using the alt/az adjusters. Perform the 2 star align, or, if you are going to be slewing from Capella to Betelguese, perform the 3 star align routine for better pointing accuracy. I use the 2 star routine because I can't always see the 3d star from my viewing location.

After each star align routine, return to the 'zero' position after adjusting the polar offset before doing another iteration.

When you get to '00-00', or as close as you can, tighten the alt and az adjusters with the allen key...they will slip if just finger tightened, and it will ruin your perfect alignment. (I replaced the thin nylon washers with 1/8" nylon washers for this reason)

Re; synching to stars. Any synch to a star will override your 2 or 3 star routine. It will improve pointing accuracy in that section of sky. I'm always synching to stars since I primarily image and need to frame up my targets..when I slew to the next target for imaging, it's always in my camera's FOV (2.25 x 1.50 degrees) so it works for me.

Once your mount is setup and marked as described, every time you set it up it will become easier and faster with better results.

Sorry for the long post, you probably know and/or do all of this, I just wanted to touch all the bases.

My mount is the V2 with the 8407 controller also.

Cheers,

Paul

#8 Stew57

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Posted 31 October 2012 - 12:44 PM

Is you mount and tripod solid? Sometimes flex can cause strange alignment mapping and affect accuracy.

#9 johnpd

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Posted 31 October 2012 - 05:12 PM

Paul,

One thing to add to "If it's off significantly horizontally in the EP, adjust the DEC manually and remark the joint.", after you adjust the Dec for being off in Az, shut down the mount and start it up again. This establishes the adjusted position as the new "Zero Position".

JohnD

#10 Astronewb

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Posted 31 October 2012 - 10:11 PM

Paul,

One thing to add to "If it's off significantly horizontally in the EP, adjust the DEC manually and remark the joint.", after you adjust the Dec for being off in Az, shut down the mount and start it up again. This establishes the adjusted position as the new "Zero Position".

JohnD


Absolutely right John...thanks for spotting that. Zero position will be lost if you don't shut the mount off at that point.

Best,

Paul

#11 Phillip Easton

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Posted 01 November 2012 - 07:13 AM


Using appropriate levels, square the mount in both axises. To minimize cone error in RA, set up your mount with the counterweight shaft aligned with the front (north) facing leg..use a plumb bob off the shaft perfectly intersecting the front leg and mark your RA basic setting. I use a small white tag on the RA joint, put a fine line on it and cut it at the joint with a razor knife, do the same with an OTA in the saddle and mark the DEC joint the same way. Now you have a 'base' repeatable setting.


Paul


I second this, a good zero position makes the whole process easier and faster. I used a magnetic torpedo level on the shaft to do RA and DEC. Also fixing your cone error is a must as well. There may be other things going on but if you don't do these you can't expect to ever get good results.

Good luck!
Phillip






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