Hello,
I am new to this forum, I am usually found in the UK-based stargazerslounge.com
If you would like to volunteer to try out a new Polar Alignment method, please let me know. The requirements are:
- You can see the Celestial Pole region from where you usually set up.
- You can attach a camera to the mount and bring the JPEG image files to your computer.
- You can freely rotate the RA axis (this excludes some AstroTrac mounts and similar, I think).
- You have Internet connectivity (to connect to nova.astrometry.net for plate solving although other local plate-solving methods will be supported in the future, such as AstroArt).
- You can run Python on your computer (e.g. Anaconda for Windows, Linux, MacOS X)
You might be able to verify your Polar Alignment within 2-3 minutes. The software will be in the public domain. It does not require a GoTo mount, it can be used to polar align even a barn-door tracker.
This is the basic idea (excuse the use of Northern Hemisphere conventions)
After a rough polar alignment, I set the camera somewhere close to declination 90 so I can see Polaris in the field of view. Keeping the camera fixed to the mount, I slew in RA by a large angle (40 degrees say) and watch where Polaris goes. If it goes off the FOV, the RA axis is not close to Polaris. So I adjust the polar alignment, bring Polaris back into the FOV and try again (the details of this iteration need to be worked out). Once it's set so that Polaris stays in FOV after a large RA slew, we are good to fine-tune the polar alignment by PhotoPolarAlign. The first two images give us the position, in pixel coordinates, of the RA axis (the red cross). I take the first image at an RA position so that the sensor is taking a picture of the sky in "portrait mode" and the second image in "landscape mode", with the long side of the sensor horizontal. The plate solving tells me where the NCP is (allowing for precession since 2000), in pixel coordinates and what the scale is. Now that the camera is horizontal, x and y pixel offsets translate directly into instructions to move the mount RA axis up-down or right-left by so many arcminutes. After I adjust the polar alignment, I take another image and check for improvement. The RA axis pixel coordinates have not changed, only the NCP pixel coordinates move. With practice, it should take only 3-4 iterations to get it close enough (whatever close enough is for your imaging needs).
The thumbnails give you a taster of what it looks like up North. A newer version will be able to deal with Southern Hemisphere.
Please download the
installer and run it, selecting your Documents folder as the destination (any folder where you have permission to write files will do).
Before running PhotoPolarAlign, you will need to have a Python 2.7 installation that includes all the modules it needs. (I used the
Anaconda distribution)
You will also need to register with
http://nova.astrometry.net/ and get an "API key".
AstroPolarAlign can be started by double-clicking the PPA.py file that the installer puts on your file system.
The first thing to do is to add the key you got from nova. Use the File -> Settings menu for that.
The second thing is to try out the supplied test image files (from the Northern Hemisphere). The two big buttons to the left of the Operations panel are used to select image files. Please select the file v.jpg for the top one and the file h.jpg for the bottom one. Hit the Solve button next to the big button, first for one image, then wait until the "Solved" label goes green, then do the second one. This will need an internet connection, of course. Once both "Solved" labels are green, you can hit the Find Polar Axis button and wait for the annotated image to pop up. Your polar alignment is also displayed on the main screen.
Then select the i.jpg file with the big button on the right side of the Operations panel. Click its Solve button and wait for a solution. Then click on "Show Improvement" button to see a new plot.
Then, exit the program and restart it to try it with your own images (the reason is that the scale is remembered in a single session but not across sessions and it's unlikely that your image scale will match the examples).
Thanks for your time, hope you will find it useful.
Themos Tsikas (themos.tsikas@gmail.com)