08-02-2019, 09:29 AM
The Canon 85mm RF f1.2 has 13 elements which have to be fatter due to it being a f1.2 lens. It is 117.3mm in length with a flange distance of 20mm. The Nikkor Z 85mm f1.8 has 12 elements and is 99mm in length with a flange distance of 16mm. That is a 18.3 + 4 = 22.3mm difference. The length of this Nikkor seems pretty right for the lens it is, then.
The Sony FE 85mm f1.8 only has 9 elements and is 82mm long, with a 2mm flange difference that makes the length difference with the Nikkor only 15mm, seems appropriate for 3 extra elements.
Now you can debate whether those 3 extra elements are worth it, them being the reason to the lens being bigger (and more expensive?). Looking the the respective manufacturer's MTF curves, the answer probably is a resounding yes.
The Sony FE 85mm f1.8 only has 9 elements and is 82mm long, with a 2mm flange difference that makes the length difference with the Nikkor only 15mm, seems appropriate for 3 extra elements.
Now you can debate whether those 3 extra elements are worth it, them being the reason to the lens being bigger (and more expensive?). Looking the the respective manufacturer's MTF curves, the answer probably is a resounding yes.