Originally posted by hypermodern
Well, the Samyang 85mm f1.8 for APS-C only weighs 350g compared with 510g for a FF 85mm f1.4 and 740g for the same specs (new design) in Nikon Z mount, so a weight saving of 30-50%. A lot lighter than to 50-135 which is covering this range at the moment.
Considering that at 85 mm, f1.8 requires a minimum objective of 47mm and f1.4 needs a 61 mm objective, 68% larger front lens area, the weight difference is easily explained. It has nothing to do with the coverage, and everything to do with the size of the front element,
The myth that crop sensor lenses should be lighter is just that, a myth. The minimum diameter of the lens barrel is determined by the size of the mount at the back and the size of the objective lens at the front.
Size and weight are largely driven by these two factors. Sure there may be some oddities out there, and things vary a lot more in the wide angle lenses with lens design, but once the focal length exceeds the registration distance things are pretty straightforward. Faster = heavier, and within the image circle limits of the mount itself, full frame or crop means very little