Tried using the solver for polar alignment but it failed all attempts. Is there a log file for this? I have all the required index files and most of the recommended index files. I can see a clear star pattern on the image captured. What may be the problem? I presume the solver is solving somewhere around where the mount is roughly pointing?

you could try to solve a captured image from the command line using "solve-field" maybe you get some errors. In ekos there is also an log field, dont you see any errors there?

It should, depending on how roughly you did initial align the scope to north.

Yeah there is like a console output a that just says "failed, try again" ...after working for quite a few minutes.

One possibility is that the focal length & aperture for your imaging scope is not correct. Take a look at the calculated FOV in the "Solution Coordinates" group under the Align tab: it should correspond to your actual field of view.

FOV per Stellarium (and Astronomy Tools site) is 1.7x1.2 deg. but solver says 102x76 mins. Ekos looks wrong - however, the data in Ekos is the same. ???
50x162mm guide scope 4.8x3.6mm CCD size

I had this problem a few days ago.

Ekos calculates the FOV dynamically, and ignores what you put. Actually overrides it by its calculation.

The way I solved it is to do a blind solve. From the command line do this:

solve-field -O --no-plots --no-verify --resort --no-fits2fits --downsample 2 your-image.fits

Then look at the output.

In my case, I had a focal reducer, which should make a 2032 mm SCT be a 1280 mm. But that was not the case, since there is a JMI EV focuser in between, making the focal length 1085 mm or so. Therefore the solver was confused when given L and H values.

So, under the Mount tab, enter the aperture and focal length, and Save.

In INDI, you have to enter the resolution for the sensor (width and height in pixels), and the pixel size. For example, for a Canon T4i (650D), those would be: 5184, 3456, and 4.3 respectively.

Then go to the Align tab, then click the Options button (bottom right of screen), then go to Solver Options.

In there, under Imaging Options, check Use Scale and Auto Update. Under Position Options uncheck Use Position.

That should get it fixed.

I never get exact results from calculators compared to solved images. However 1.7x1.2 deg and 102x76 mins is quite the same.

As 1 deg = 60', 1.7 x 1.2 deg is actually equal to 102' x 60'. If the size of the sensor is w x h and the focal length of the scope is f, then the FOV is given by

FOV = 2*atan(w/2/f) [horizontal] ; 2*atan(h/2/f) [vertical]

And by entering the figures given by @gbeaton we get a FOV of 1.698 x 1.273 deg, which is in line with values reported by Ekos and by online calculators. Now, this value may be a little bit different compared to solved images due to the fact that actual focal length may be slightly different from nominal focal length, see also @kbahey post.

Some questions for @gbeaton:

1. Are you using real hardware or simulators in your test?
2. Did you tried Online solver mode? Do you get the same results (failure)?
3. If you use Load & Slew with a real image instead of Capture & Solve, does anything change?
4. If you manually upload your captured images to astrometry.net, do you get a solution?

@alessio.beltrame, this hobby is going to kill me I guess I was too tired to see that the FOVs were the same. I'll try your suggestions when I get a chance. Weather here is bad and it doesn't get properly dark until after 10pm. I thought solving would help me speed up polar alignment but in fact I have to wait a long time before there is enough contrast in the sky to use it. If I could accurately polar align with it in a few minutes, then its worth it.

@kbahey, unchecking use position seems like it will hinder the solver. What exactly is this option doing?

Here is a tip: If you are not sure about the final focal length, go to Astrometry.net settings and turn Verbose on, then go to Solver Settings and uncheck "Use Scale",. Ekos would not send the calculated scales from the FOV to the solver. After an image solves correctly, you can find the FOV as measured by the solver. From this value, you can calculate your effective focal length that you need to use.

In theory, disabling the two options will hinder the solver. In reality, it does not hinder it much though, provider you are on a regular Intel laptop (I have not tried this with a Raspberry Pi, with a slower CPU).

You can also try uploading the image manually to nova.astrometry.net/upload without any hints or options. After a minute or two, you will have a solution. It is very consistent, and never failed for me.

Disabling the imaging options and position options will force a blind solve (just like you do with the web site above). This is useful if the scope points to the wrong part of the sky for some reason.

So, in summary: do a blind solve, either from the command line, or by disabling Imaging and Position Options. Once you get a focal length from the solver, then enter that under the Mount tab in Ekos, as well as in INDI, then re-enable the Imaging Options, and a FOV will be calculated for you, and you are good to go.