Hello there!
Before making this thread i have searched this forum + Reddit’s one.
While people already asked questions about perspective distortion etc, nobody actually answered the single question i have seen there - how to deal with perspective, when bounding box triggers Auto-Crop feature?
What i mean: When i you start with a sphere or use head base, the focal length works quite good, because model’s bounding sphere (idk how it’s called properly, sorry) covers it close to the forms, which means AC triggers only when camera is REALLY close.
But, as soon as you start to add other subtools, like, adding another sphere and shaping it to form the body, then you add legs, arms etc, that bounding sphere no more resembles the head forms and now covers entire model and that means, AC starts to trigger way sooner than before. And when i need to zoom closer, it doesn’t match previous focal length or Angle of View (so problem exists in both old camera and new universal one).
So, the question is simple, how to deal with it? HOW should i work with references e.g. when i have full body base, especially when i need to match head part?
One would say it’s ok, it’s how ZBrush works and i shouldn’t care that much, but they don’t see the problem, you won’t be able to match the reference, as focal length breaks(doesn’t update) when you zoom in. Hiding part of mesh/subtools doesn’t do anything, it still counts as if mesh is fully seen. I totally understand why it happens, but i don’t understand how to work with it.
P.S. i am sure everyone understand what i am talking about, but if it’s not the case, here are steps to reproduce the problem:
-open head base in light box
-append any subtool/primitive
-zoom camera closer to face
-then adjust position of appended subtool through menu(i used Y axis, as its the way i would build up my model)
-see how perspective changes
P.S. 2 The issue is also bound to document size/full screen mode and focal length value.
E.g. if i have document size at maximum available resolution of my monitor, it triggers perspective change at about 7 Y units. If i limit ZBrush window to half of my monitor (i have 21:9 ultawide) and adjust document size accordingly that window, it starts to trigger at 5 Y units(but this value changes if you have different focal length values).
Plus, AC is affected by focal length value. If i have focal length at 35mm as on the screens, in current example perspective change starts to appear when cylinder is translated to Y=4 units. If i have focal length set to 50mm, it starts change at Y=5 units translated.
This is pain 
Two screens:
