Putting old lenses onto hew, high-performance DSLR or mirrorless cameras seems counter-intuitive so why would anyone want to? The simple answer is that many older lenses can capture images that have that elusive quality known as character. For photographers or videographers who want to create unique images that express their personal style, character can be even more important than resolution numbers, corner-to-corner sharpness, and other advantages of the near perfect lenses that are quite common today.
The imperfections and aberrations of older lenses are the very strengths that set them apart from modern lenses. Additionally, a fully mechanical lens is likely repairable longer and less expensively than modern focus-by-wire lenses. Old lenses also let you change camera systems, or your mount can get retired and your lenses won’t be bricked. At the extreme case, some mirrorless lenses require firmware updates for every new body, so even if the mount stays around lenses won't stay on that update list forever (for instance Nikon's new E lenses are incompatible with cameras just two generations old).
