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Limiting Rotations to 0 and 90 degrees

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#1 mshetzer

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Posted 03 December 2023 - 12:07 PM

I am using NINA with a Moonlite Nightcrawler Rotator/Focuser.  I've been letting NINA plate solve (Slew, center and Rotator) and take care of the object rotation between targets.  I only shoot 0 and 90 degree targets.  Unfortunately, I am getting 0 and 180 degrees for 0 degree object targets, and 90 and 270 for 90 degree object targets.

 

I believe this is going to cause me a bit of a headache when I calibrate with my flats in Pix Insight (Please let me know otherwise), as I'll need to produce flats for each of the rotations.

 

I'd like to limit the rotations to 0 and 90 degrees and see that there are two ways to do it.

 

1.  In NINA, under Equipment>rotator> I can limit mechanical range down to 90 degrees.  I would assume this would just shoot my targets at 0 and 90.

2.  In the Ascom driver, I have the option to restrict the Rotation.  I'm not sure if this is mechanical, but if so, I would set at minimum 125 mechanical to 216 mechanical.  I am assuming (lots of assuming going on here) that if the rotator wanted to shoot at 180 object degrees, it would go to 0 object degrees.

 

I'd love to hear what others are doing.

 

Thanks,

Matt

 

 

 


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#2 DaveDE

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Posted 03 December 2023 - 01:59 PM

I just went through this with NINA and my Nitecrawler. It's confusing.

 

First of all, I wanted the reported orientation of the camera to agree between NINA's plate solver and the Nitecrawler. Before the situation was resolved NINA would say the position was at one location and the Nitecrawler would say another but now they agree and are limited to rotating between +/- 90 degrees but 0 to 90 should be easily settable as well.

 

Here's what I did:

 

1. Rotate the position so that the camera horizontal (long) axis is parallel the the RA axis, zero degrees.

2. Disconnect the rotator from NINA and connect to it with the Moonlite Nitecrawler application. Click on the center of the rotation dial and set the GOTO degrees to 0. Click OK and then Click SET POS. This will set your rotator to read 0.0 degrees at this position. Now NINA and the Nitecrawler will read the same thing no matter what position the rotator is in.

3. In NINA, open the Ascom Nitecrawler Setup app. Make sure Reverse is NOT checked and enter your 0 and 90deg limits or what ever limit you want.

4. In NINA, go to the Equipment/Rotator menu for the Rotator and make sure reverse is OFF and set Mechanical rotation for Full. I don't know why this has to be set for full but in my case it does. The Ascom limits will limit your rotation.

 

Hope this works for you, it did for me.

 

Dave

 

p.s.

If you use PHD2, configure it to recognize your rotator and you will not have to re-calibrate every time you rotate the focuser. On the Connect Equipment screen, add the rotator and on the Advanced Settings/Devices menu check the Reverse Sign of Angle box


Edited by DaveDE, 03 December 2023 - 02:02 PM.


#3 Alex McConahay

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Posted 03 December 2023 - 11:57 PM

>>>>>I only shoot 0 and 90 degree targets.  Unfortunately, I am getting 0 and 180 degrees for 0 degree object targets, and 90 and 270 for 90 degree object targets.

I believe this is going to cause me a bit of a headache when I calibrate with my flats in Pix Insight (Please let me know otherwise), as I'll need to produce flats for each of the rotations.

 

 

>>>>>I believe this is going to cause me a bit of a headache when I calibrate with my flats in Pix Insight (Please let me know otherwise), as I'll need to produce flats for each of the rotations.

 

Lets talk about two operations in image processing, Calibration and Registration. 

 

Calibration (darks, flats, bias) uses the orientation of the pixels on the sensor. That does not change from lights, to darks, to bias, to flats. No matter what the file is saved with the pixel in the upper left (or bottom left, or some set location) is 0,0. All the other pixels just take their place in line behind that. A given position always reports in that position whether gathered from a light, flat, dark, or bias. So, it does not care what your telescope orientation is. 

 

Whether the sky is at 90, or 270 or anywhere else is immaterial in calibration because the process relies solely on the location of the pixels on the sensor (which does not change between lights, flats, darks, or bias.)  

 

So, Calibration does not care at which orientation you took the frames. 

 

>>>>>>>I only shoot 0 and 90 degree targets.  Unfortunately, I am getting 0 and 180 degrees for 0 degree object targets, and 90 and 270 for 90 degree object targets.

 

 

On one side of the meridian, your object will be at 0 or 90 degrees. But that same target will be at 180 or 270 after the meridian flip. After all, that is what the telescope does at meridian flip----it flips 180 degrees, making 0 int0 180, and 90 into 270. Images taken at 0 and 180 are identical to each other, and 90 and 270 are similarly identical to each other, except that they are flipped. All you have to do in processing these images (after calibration) is flip half of them back over.

 

The process that does this is registration (star alignment in PixInsight).  That is, they are analyzed for the star positions, and matched to a "master frame" (which includes being "flipped" to have all the stars (and every other value of the pixels across the frame). 

 

Note that flipping of star positions is not the only thing going on in registration. The frames are moved around so that the features in one are in the same position as the features in every other. If there has been a shift of some sort (bad guiding, poor tracking, many other things) the frames can also be stretched, shrunk and such. This brings all the bright spots back into the same place relative to those bright spots in every other frame. 

 

After calibration (which cares only about pixel location on the frame, regardless of orientation) you register (which makes sure any stars and nebulosity line up, even it means flipping the image, stretching or shrinking it, or whatever. 

 

In other words, it is not a problem. 

 

Alex

 

(Okay----I have to tell you that if for some reason your light path is not symmetrical (shaped the same way no matter which way you turn it) then what I just said needs some clarification. But it is extremely rare that a light path is not symmetrical. )


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#4 joshman

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Posted 04 December 2023 - 12:39 AM

I am using NINA with a Moonlite Nightcrawler Rotator/Focuser.  I've been letting NINA plate solve (Slew, center and Rotator) and take care of the object rotation between targets.  I only shoot 0 and 90 degree targets.  Unfortunately, I am getting 0 and 180 degrees for 0 degree object targets, and 90 and 270 for 90 degree object targets.

 

I believe this is going to cause me a bit of a headache when I calibrate with my flats in Pix Insight (Please let me know otherwise), as I'll need to produce flats for each of the rotations.

 

I'd like to limit the rotations to 0 and 90 degrees and see that there are two ways to do it.

 

1.  In NINA, under Equipment>rotator> I can limit mechanical range down to 90 degrees.  I would assume this would just shoot my targets at 0 and 90.

2.  In the Ascom driver, I have the option to restrict the Rotation.  I'm not sure if this is mechanical, but if so, I would set at minimum 125 mechanical to 216 mechanical.  I am assuming (lots of assuming going on here) that if the rotator wanted to shoot at 180 object degrees, it would go to 0 object degrees.

 

I'd love to hear what others are doing.

 

Thanks,

Matt

I've recently got myself a mechanical rotator, and i've found the way the NINA handles it to be...confusing, or at least not overly intuitive. I've got my "home' position for my rotator at 90 degrees mechanical angle, and I've aligned my camera to this angle as well. that way all my planning will be talking the same angular language. From here I can get a full range of image rotation by only rotating 90 degree to either side. I'm very conscious that i do not want the EFW rotating below the plane of the OTA mounting plate, as there are points in my sky where this would hit the tripod/mount/etc.

 

I've had instances where i would line up a target in the framing wizard at a 30 degree angle, and ask it to slew center and rotate. it would slew fine, then it would start rotating the wrong direction, then it would keep trying to adjust the rotation angle to try and get itself lined up properly, it would eventually hit the 5-try limit and fail.

 

Because I've found it to be non-intuitive at how NINA is handling to the rotator and rotation commands, I'm not using the slew, center and rotate instruction. I'm taking the bull by the horns (so to speak) and am setting the rotator position manually in my sequences. that way i can be sure it's rotating to the correct angle, and keep it there for my flat frames.

 

I write the rotation angle into my file name and folder structure, and take flats immediately following the target. (it only takes 6 minutes to run a full flat frames cycle for 7 filters, including closing and opening the flip flat cover.)

 

It'd be nice if there was a "Slew, Centre and Mech Rotate" option. I envision you could set mechanical angle limits and NINA would only compose within that window, making necessary calculations for different sides of the pier. ie. 145 degrees is compositionally the same as 325 degrees. I'm sure that is the intention behind the existing NINA limits, but i haven't seem them work that way.
 


Edited by joshman, 04 December 2023 - 12:43 AM.


#5 ghilios

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Posted 04 December 2023 - 06:25 AM

Check out the mechanical rotation limit in the rotator equipment tab. You can pick 360, 180, or 90.
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#6 mshetzer

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Posted 06 December 2023 - 01:55 PM

Thanks for all the great information !!!

Matt




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