Originally posted by Sandy Hancock On both counts it must give a less shallow depth of field wide open at the same focal distance as the FA*85/1.4 wide open, regardless of sensor size.
Nothing works "regardless of sensor size".
In particular, at the same focal distance (say 3m in both cases), the 77/1.8 @ f/1.8 produces a shallower DOF on APS-C than the 85/1.4 @ f/1.8 does on FF.
That's what I meant in my original post. The reason is that the APS-C format requires a higher magnification factor to produce the same output size (e.g., a 8x10 print); this reduces the DOF (as the blur discs are more enlarged than those of the FF image).
Originally posted by beholder3 If same space/distance: both combos create pretty much the SAME DoF (e.g. 9,8 vs 10,2 cm).
At 3m and f/1.8 I get 10.2cm for the 77/1.8 on APS-C and 12.7cm for the 85/1.4 on FF (so the 77/1.8 has shallower DOF, as I said).
Originally posted by beholder3 If same framing: FF/85 1.4 has about half the DoF of APSC/77 1.8.
At 3m (85/1.4 @ f/1.8 on FF) vs 4.19m (77/1.8 @ f/1.8 on APS-C) I get 12.7cm vs 19.4cm, i.e., the 85/1.4 has about 65% the DOF.
Of course, the "same framing" comparison is the one to make for (as closely as possible) "equivalent" images. In my post above, I assumed "same distance" for simplicity (we were already assuming the same f-ratio), which I should have pointed out.
Originally posted by beholder3 DOF simulator - Camera depth of field calculator with visual background blur and bokeh simulation.
That's the nicest I've ever seen!