The focal length always appears in my FITS headers. Of course, if we change focal lengths while keeping the same mount, it's up to us to make the change in the train specifications. Another option is to have a unique Ekos name for each focal length that uses the same mount.

This obviously doesn't solve the file name problem. However, if you have a bunch of files and you're not sure of the FL for each one,
grep -l 1.55 *.fits > 155files
will put the name of every FITS file that has 155 as its focal length into a file named 155files. Note that the internal FL storage in a FITS file is in exponential format, e.g., 1.55E+02

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