What is the difference between symmetric and asymmetric lenses? I googled but didn't get satisfied results...
with symmetric lenses the rear elements are exactly the same than the front elements, but in case of wide angles the lens has to come very close to the capture unit ( as film or digi back ), therefor symmetric wides cant be used with mirror boxes in between.
distortion can be removed completely because the rear element distorts in the same way ( but in the opposite direction ) than the front elements. so theses two distortions eliminate themselves, tieory to 100% but of course there are production tolerances between the single lense elements. ( exist the same in the audio world with symmetric cables ...).
unsymmetric lenses can be mounted more far away ( in case of wides ) to reach this the lrear element of the lens has to be a different constrcution
than the front element, in ths way it projects the image farer away ( or closer in case of tele lenses).
because this two basic lens elements are now different their distortion is also different and the optical elimination of the distortions is not working anymore,
at least not to 100%. results are visible distortions.
image: high rise detail .