Originally posted by JeffJS The APS-C sensor is 2/3 of a 35mm frame (23.4 x 15.6 mm), not half..

Sorry to be pedantic -

Actually RioRico was more correct by area....

23.4mm x15.6mm = 379.08 sq mm

Full-Frame is

36mm x 24mm = 864 sq mm

so APS-C is actually 43.875% of a Full-Frame

Just to be sure -

if we took a piece of paper and wanted half the size -

we'd cut it in half......

that is by area,

not by linear (one dimensional/length) measurement -

the linear scale would be the square root of 2.

However in mitigation, focal length coverage is calculated by the ratio to the diagonal of the film/sensor frame and this is linear

- that's where the crop factor comes from.

85mm was a close portrait lens for Full-Frame - since APS-C has a crop factor of 1.5x

- to get the same equivalent focal length one would need about 57mm.

So a cheaper and more common 50mm f/1.4 or f/1.7 lens would probably be more suitable -

which would be a 75mm equivalent in FF.