In this year's A1 print set received from the lab, two of the prints showed out of focus areas that were looking fine on my (smaller) display. So, I revisited how I selected my exposure setting (see P mode / hyper program thread), but also I checked again the depth of field matter, opened up the online advanced DoF calculator from photopills here
https://www.photopills.com/calculators/dof-advanced. However, after entering a few value sets , I got confused by the depth of field results the simulator provided me with. , until I realized that the classic format equivalence doesn't work for me (unless I didn't understand correctly).
Considering prints (or display), it looks like classic equivalence only work if display output size, viewing distance and viewer visual acuity are all fixed (e.g fixed to 8x10" at 14" viewing distance, 20/20 vision). For example, for same display / viewing conditions, the perceived depth of field from an FF 85mm f/8 image would be matched by an APSC 56mm f/5.6, that's the classic equivalence. Now, considering that a FF 85mm f/8 image would be enlarged 1.5x more than the APSC image for display (e.g taking advantage of the extra resolution of the FF camera), the classic equivalence is broken, and that case the depth of field (blur) of the FF 85mm f/8 image would be perceived like an APSC 56mm f4 image.
So, in practice, there isn't only one stop difference between FF and APSC , but it's two stops. Taking another example, from FF image to Phase One image printed 2x larger than the FF one (crop factor 0.5x), for the Phase One to match the FF depth of field its lens should be stopped down by as much as 4 stops, that's huge. And from FF to 4x5 (crop factor = 0.27), for making 3x larger prints out of the LF camera, I would have to stop the LF lens by 8 stops from FF aperture values (e.g FF lens aperture f/5.6 => LF lens aperture ~ f/100), leading to super slow shutter speeds in the LF camera. Did I understand correctly?
Last edited by biz-engineer; 12-08-2021 at 04:37 AM.