Thank you for these valuable informations
I'm using knighty's formula
Acutally it's Buddhi's formula.
I've just modified it a little bit. I think it can be improved further.
BTW! the statment:distance = (sqrt(x*x+y*y+z*z)-abs(scale-1))/abs(DEfactor) - abs(scale)^(1-i);
is over complicated. Now i do instead:distance = (sqrt(x*x+y*y+z*z)-BVR)/abs(DEfactor)
BVR is the radius of the bounding volume of the fractal.
It's possible to use max(max(abs(x),abs(y)),abs(z)) as the norm instead of sqrt(x*x+y*y+z*z). This is not an optimization, just another way to do it.
In case you are interrested, it's also possible to keep the size of the (positive scale) mandelbox constant.link