Samyang 135mm f/2.0 ED UMC Canon EF astronomical review
Astrophotography is a type of astronomical observation in which images of celestial objects are taken. For astrophotography, it is not necessary to use a telescope – a photographic lens can be used as an astrograph. However, such photographic lenses are subject to completely different requirements than for everyday photography – good sharpness across the entire field is required, as well as minimal distortion (aberrations) even when shooting with a fully open aperture. Accurate centering of the lenses in the lens is very important.
For rapid accumulation of light, a high aperture ratio is desirable. This is especially true for short summer nights.
One of the most important parameters of a photographic lens is the focal length. The longer the focal length, the larger the size of the object image on the photodetector. There is no such thing as magnification in astrophotography, since the size of the image on the screen may vary, as well as the distance from which the image is viewed. However, one can very roughly imagine 1x magnification as looking at a 10×15 cm photograph from a distance of about 30 cm, obtained using a 50 mm photo lens and a camera with an APS-C format matrix (about 25.1 x 16.7 mm). Then the angular size of the object in the image will coincide with the angular size of the object in the sky.
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