Author Topic: Up and to the Right?  (Read 314 times)

veworltonuc

  • Active Astronomer
  • ***
  • Posts: 128
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Up and to the Right?
« on: December 30, 2017, 12:24:55 AM »
Hi guys,

When performing the goto alignment for my AVX mount, I finish centering the object by moving the star Up and to the Right until it is centered. By up and to the right, I mean that when I am looking through the eyepiece at the star, I move it up and to the right in the Field of View. This doesn't necessarily correspond to pressing the Up and Right buttons on the hand controller.

I have looked through other forum discussions and see both answers... Which is correct?

Thanks in advance!



adtalhalyg

  • Active Astronomer
  • ***
  • Posts: 115
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #1 on: January 03, 2018, 09:01:44 AM »
I'm assuming that you are not using a 45-Degree Erect Image Diagonal ( http://www.celestron...-image-diagonal ), correct? Normally, the stars you see in your eyepiece are reversed from their true orientation: https://sixalberts.f...ge-rotation.jpg

behelphyri

  • Active Astronomer
  • ***
  • Posts: 119
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #2 on: January 10, 2018, 04:06:35 AM »
Recently, I have been using my ccd camera instead of the eyepiece (I am doing astrophotography). So yes, no diagonal is being used.

However, just for my knowledge, if I was using my 90 degree diagonal and an eyepiece, how would this affect my approach? Would I perform the inverse?

Matt Haines

  • Active Astronomer
  • ***
  • Posts: 122
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #3 on: January 13, 2018, 08:15:16 AM »
On Page 17 of the Celestron AVX Mount Instructions (http://www.celestron...VX-Manual-F.pdf), it says that "The hand control has four direction buttons in the center of the hand control which control the telescope motion in altitude (up and down) and azimuth (left and right)." On Page 18 it also says:

"Direction Buttons – The direction a star appears to move in the eyepiece changes depending on which side of the Meridian the telescope tube is on. This can create confusion especially when guiding on a star when doing astroimaging. To compensate for this, the direction of the drive control keys can be changed. To reverse the button logic of the hand control, press the MENU button and select Direction Buttons from the Utilities menu. Use the Up/Down arrow keys (10) to select either the azimuth (right ascension) or altitude (declination) button direction and press ENTER. Select either positive or negative for both axes and press ENTER to save. Setting the azimuth button direction to positive will move the telescope in the same direction that the telescope tracks (i.e., towards the west). Setting the altitude buttons to positive will move the telescope counterclockwise along the declination axis."

rentireacen

  • Active Astronomer
  • ***
  • Posts: 109
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #4 on: January 13, 2018, 04:53:49 PM »
Quote
Hi guys,

When performing the goto alignment for my AVX mount, I finish centering the object by moving the star Up and to the Right until it is centered. By up and to the right, I mean that when I am looking through the eyepiece at the star, I move it up and to the right in the Field of View. This doesn't necessarily correspond to pressing the Up and Right buttons on the hand controller.

I have looked through other forum discussions and see both answers... Which is correct?

Thanks in advance!


Using the up and right keys and not worrying about which directions they correspond to in the eyepiece is the correct way. Padawan.

ceplinglittfi

  • Active Astronomer
  • ***
  • Posts: 104
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #5 on: January 13, 2018, 11:25:04 PM »
Quote
Recently, I have been using my ccd camera instead of the eyepiece (I am doing astrophotography). So yes, no diagonal is being used.

However, just for my knowledge, if I was using my 90 degree diagonal and an eyepiece, how would this affect my approach? Would I perform the inverse?


It wouldn't affect anything, since the key is the up and right keys, NOT directions.

Freddy Banks

  • Active Astronomer
  • ***
  • Posts: 110
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #6 on: January 14, 2018, 01:56:33 AM »
The reason for up and right is simple - and that is to take out backlash. But I'm actually not sure it is always set up properly when using a gem like my cge-pro.

It's easy to see if it is correct because when you slew to an object - the mount quickly goes nearby - and then does a slow diagonal slew to the final location. You want your final button presses to match that final direction of motion - and it doesn't matter what the manual says or what the advice is - to take out backlash both final approaches should be the same.

I'm not sure - but I have the impression at least one of the buttons, probably n/s, changes direction on the other side of the meridian. But I could be wrong. To make matters worse, I often use the ascom controller and its small pad of arrow keys to center the object - and it may have its own version of up and right different from the hc.

Anyway - the reason for doing it is simple, and it's easy to observe the final approach direction and match it - especially if you are watching the cursor on a planetarium program as the mount moves. But there may be situations where up/right is actually the wrong thing to do - and it may depend on which keypad you are using.

It doesn't make a huge difference either way - but if you want most accurate goto then you want to remove the impact of backlash wherever possible.

Frank

breakagalkit

  • Active Astronomer
  • ***
  • Posts: 115
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #7 on: January 21, 2018, 06:34:12 AM »
No, the buttons don't change. You'll be OK if you just do final centering with the up and right KEYS without regard do their relationship to directions in the eyepiece. This can help all the Celestron GEMs regarding their goto accuracy, but obviously those with the most inherent backlash are helped the most.

Derek Vail

  • Active Astronomer
  • ***
  • Posts: 137
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #8 on: January 22, 2018, 08:48:04 PM »
And I'll just add for clarity - you should go down and/or left if needed so that the up and right keys can be used for the final position.

smalmonica

  • Jr. Astronomer
  • **
  • Posts: 88
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #9 on: January 30, 2018, 01:19:48 AM »
My normal process for centering an alignment or calibration star is this:

1) Get star near center

2) Press down and left keys to move star towards edge of field. Make sure to move it far enough that it takes up backlash in each direction (if it takes a moment before it moves, this is taking up the backlash)

3) Press up and right keys to do final centering. If I overshoot the center, go back to step 2.

Also note that if you don't have a reticule eyepiece, it helps to defocus the star into a donut. Your eye can naturally see concentricity of larger circles easier than it can determine if a point is in the center of a large circle.

Grant Buchanan

  • Active Astronomer
  • ***
  • Posts: 120
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #10 on: February 02, 2018, 04:24:34 PM »
Let me add that the documentation for the more recent releases of the firmware for Synta's SynScan mounts also recommends "up and right."

Cesar Rojas

  • Active Astronomer
  • ***
  • Posts: 128
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #11 on: February 03, 2018, 12:21:49 AM »
Quote
No, the buttons don't change. You'll be OK if you just do final centering with the up and right KEYS without regard do their relationship to directions in the eyepiece. This can help all the Celestron GEMs regarding their goto accuracy, but obviously those with the most inherent backlash are helped the most.

I think it may not change when using the actual handcontrol - but it will likely change when using the ascom keypad or something else for that final direction. My scope is outside - so I can center the object on the ccd remotely using the ascom keypad - when doing a realignment on two stars.

My main point is that there is a reason for doing up/right - and you can check and confirm if it is the right thing to do or not. I believe the final approach is from the south on one side of the meridian, but from the north on the other. This makes sense because the motor is turning the same way in both situations.

But if you then do final motion with a button that means actual north or south direction - it will need to be up right on one side and down right on the other. Or it may even be up left and down left.

Unfortunately I can't confirm right now, but anyone with a planetarium program can watch the final approach on a goto - and then watch what up/right is doing - with whatever keypad they use. The final movements to remove backlash should match whatever direction that final slow movement was in.

Frank

Stanley Elliott

  • Active Astronomer
  • ***
  • Posts: 132
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: Up and to the Right?
« Reply #12 on: February 09, 2018, 10:41:56 AM »
With an east-heavy mounting on a GEM, the "to the right" makes sense, as you are eliminating the backlash on the RA gear, and the mount is resting a little heavy on the worm.

The "up" part makes no sense, however. If you have perfect polar alignment, then the mount could be either naturally meshed to the N side of the DEC worm or the S, depending on how the scope is mounted.

Unless you bias your declination as well, knowing your bias in the RA, and creeping up against that bias when finishing a slew is all you need to do.

So the rule - "up and to the right" for practical non-specialized purposes, assuming you balance east heavy, should just be "to the right". Right?