Hi all,
I was wondering if it is at all possible to work out the Telescope Focal Length from an image taken with a Camera. For instance, I used the website
http://nova.astrometry.net on an image I took (below). On successful completion of the image, the website tells me I have a 2.77° x 1.84° FOV with a pixel scale of 4.98 arcsec/pixel and a radius of 1.66°
Given the above information and adding the other known values such as I was using a Canon 400D, and the telescope I was using has an aperture of 80mm. Can we then work out the focal length the image was taken at?
Links to the annotated images using Astrometry.net
M8 and M20
NGC 4945
Images below...