Hi there,
I am relatively new to using SGP and Astrophotography in general, but I’ve been able to take some images of galaxies and stars with SGP.
I’ve been getting a problem however when I try to plate solve and centre using PlateSolve2. I get an error saying the “Plate Scale hint is not within 25% of the hinted pixel scale” or something rather.
I had thought that I set up the pixel scale properly, both in the Control Panel and Equipment Profile Manager. But maybe it is not the case.
The equipment I am using (I’m based at a University):
14" Schmidt Cassegrain
Focal length: 3910mm
Camera:
Atik 383L
Pixel size: 5.40 microns
Reducer Lens:
0.63 Celestron Reducer
I am led to believe that it is the pixel scale that is causing the problems, but I am not sure how I can fix it. (tried to upload the log file but couldn’t for some reason).
According to Astronomy.tools the pixel scale on that setup should be about .50
If I remember correctly, you can specify the pixel scale in the equipment profile.
If you can get an image to plate solve, it should show you the actual pixel scale and you should be able to figure out the actual focal length as well.
Most plate solvers require hints in order to succeed. A hint is comprised of an approximate location and an approximate scale. It’s not a guarantee that the solve is bad if you see that warning as some solvers are more robust than others, but at the very least, it’s a note that your 1x1 image scale in the camera tab can be more accurate. There is a calculator button next to the scale field and it seems like you have all of the parts of the equation that are required to generate a (reasonably close) scale value.
Ok so after importing one of my photos into AstroImageJ (I use this for producing transit plots) and checking the fits header, the image dimensions itself are 1677 pixels x 1264 pixels.
This is probably what is causing the errors in plate scale because I am saying the image dimensions are 3354 pixels x 2529 pixels. But how is this possible when the Atik 383L has a sensor size of 3354 pixels x 2529 pixels? I thought I had to put in the default size of the sensor as specified by the manufacturer.
Seems you are using a binning factor of 2x2 then, this results in an image size with 50% of the pixels in each dimension (so 25% of the total number of pixels), but those pixels are then also twice as big in each dimension (thus four times the surface of the sensor pixels).
Ok I have solved the problem, thank you to everyone who responded; your comments cleared up some misconceptions I had.
The problem was indeed the plate scale. It was 0.59 "/pixel instead of what I thought it was (0.452 “/pixel). I believe this is a result of the ‘guesstimation’ of the focal length of my 14”; I can’t find the exact model online and it is somewhat old.
What I did to solve the issue, for future reference, was this. Take a single image, doesn’t matter where, right click (windows) and ‘Plate Solve’. Mine plate solved easily and asked if I wanted to use the information in Target 1 of the sequence, which I did. Within this information was the pixel scale, which I yoinked and updated my profiles/equipment with. After this, I had seemless plate solving facing Eastward, and hopefully it will stay that way.
For any other users that might have this problem in the future, plate solving the image firstly before slewing seems to give you the correct pixel scale regardless of what you think it might be. As in my case, I assumed the focal length on my scope was 3910mm and 2463mm with the reducer. In reality, this might have been shorter which caused the pixel scale to be larger as a result.