You don't actually need the focal length, it doesn't help accuracy that much but can help you line up the sky to the photo a bit quicker. Anyway, if we did, all that info was in the metadata anyway:
Camera: Nikon D5
F-stop: f/2.8
Exposure time: 5 sec.
Focal length: 28mm
Max aperture: 3
Camera: Nikon D5 F-stop: f/2.8 Exposure time: 5 sec. Focal length: 28mm Max aperture: 3