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Thanks to the moon's libration (wobbling effect), 59% of its surface is observable from Earth. The maximum libration angle is: 1.54° (equator to ecliptic inclination) + 5.15° (ecliptic to orbital plane inclination) = 6.69°. Libration occurs in both lunar latitude and longitude. Visualization
When using a barlow the effective focal length often is not the barlow factor but depends on its position in the optical train. The further away from the camera sensor the larger the magnification. Most barlows come with sleeves, others as lens units, the latter, when directly threaded to a camera, often provide less magnification than their specified barlow factor. Consequently, image scale and FOV are based on maker-specified values, therefore, approximate. Also, the actual focal length of an SCT varies with the position of the primary mirror while focusing.
