When working in perspective mode - if you add another subtool to your model then the whole perspective of your model will change.
This can be rather painful if you’ve spent hours lining up your object to a background image. grrr
It would appear that perspective chooses the center of your object as the focal point rather than the center of the canvas. So adding a new subtool to the side of your object will obviously change its center. double grrr
have to agree this is annoying, although i swear i read that in the mac 3.12 this is fixed, hope so for 3.5.
I was just reading the help info on the perspective button and apparently we’re supposed to be able to select a universal vanishing point by holding shift and dragging a picker from the focal length slider to the desired area on the canvas. Later we’re supposed to hold shift and click the perspective button to use the selected vanishing point.
Doesn’t seem to do anything though…
once again working from a faulty memory here, i think that this no longer works this way since 3.0, i remember marcus saying he’d let the development team know.
Yep, I just did a search and found a thread where Marcus replied saying that it no longer seems to be working. 
Thanks anyway, Spacey!
yeah it would seem that since 3.0 zbrush’s direction isn’t really image making anymore, just modeling. lights,layers, 2.5d brushes didn’t get much of a make over at all and even lost some functionality like the perspective issue. makes me sad.
Well it’s not really image making that I’m doing. But rather making a 3D model using a large image in the background as a reference.
Anyway, I think I’ve come up with a solution to my problem!. I’m going to place a large dummy object around my main object. Hopefully this way ZBrush will take the larger object into account when determining where the focal point is. I’ll then be free to hide the smaller subtools without having the perspective shift around.
Hopefully…