As many people may have been aware of, Zbrush utilizes a different camera system from other traditional 3D packages and traditional photography. It’s been a pain in the rear when one tries to get a precise perspective inside of Zbrush.
For instance, the “FocalLength” slider adjusts a combination of “dolly” and “zoom” in terms of camera movement, whereas “focal length” in a traditional term is only responsible for “zoom”. The values of Zbrush’s FocalLength have no direct correspondence to the traditional term as well.
Also, when importing a model, Zbrush will automatically adjust it’s camera placement in order to frame the model, while the value of FocalLength remains unchanged. Which means a FocalLength=70 for one model may have a totally different perspective outcome from another model with the same value at 70.
With some personal experimentation, I attempted to study the mechanism behind Zbrush’s camera work, and came up with the following. I’ll call it “AP-ZBP-Law”, or “Aquaplatina’s Practical Law of Perspective for Zbrush”.
Hope some would find it useful.
AP-ZBP-Law
Description Terms:
FL=traditional focal length
ZFL=Zbrush’s FocalLength slider
D=distance between the camera and the center point of a model
CL=length of the space diagonal of the cuboid formed by a models width/length/height
- A model’s perspective is directly related to the model’s physical size and “D”. When adjusting both the model’s size and “D” in a proportional manner, the model’s perspective remains the same.
- “ZFL” adjusts both “D” and “FL”. For a constant model, “ZFL/D/FL” are all proportional to each other while adjusting “ZFL”. However, Zbrush’s “scale” function can also be viewed as a change in “FL”, which leaves “FL” totally random inside Zbrush.
- Zbrush adjusts “D” in order to frame models with different sizes, but “ZFL” does not adjust accordingly. For each model, when ZFL=70, D=CL/0.577.
*The experiments were done in Zbrush 3.1 and Maya 2008. Its adaptability to other versions and software is unknow.
**These laws were results of Aquaplatina’s personal experimentation. I take no responsibility for its accuracy.
***0.577 in Law 3 is an estimated number rounded to three decimals. Resulted errors are expected to be within practical range.
****By any chance are official numbers disclosed to the public, it shall take the place of Law 3.
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Example 1:
A model measures 1x1x1(inch), CL=1.732(inch).
From Law 3, when ZFL=70, D=1.732/0.577=about 3(inch).
From Law 2, when ZFL=70/2=35, D=3/2=1.5(inch); when ZFL=702=140, D=32=6(inch).
Take the same model into Maya 2008, set “D” to 1.5/3/6(inch), when get the same perspective as in Zbrush when ZFL is set to 35/70/140.
Example 2:
A model measures 2x2x1.732(inch), CL=3.317(inch).
From Law 3, when ZFL=70, D=3.317/0.577=5.749(inch).
From Law 2, when ZFL=70/2=35, D=5.749/2=2.875(inch); when ZFL=702=140, D=5.7492=about 11.5(inch).
Take the same model into Maya 2008, set “D” to 2.875/5.749/11.5(inch), when get the same perspective as in Zbrush when ZFL is set to 35/70/140.
