Hello Marco,

In your TTHI operands, there’s a column Adjust, which contains a surface number. This column tells OpticStudio to adjust the thickness of the corresponding surface based on the tolerance applied to the surface (Surf) of the TTHI operand. This is an excerpt from the Help File (F1) about TTHI:

To illustrate, imagine a lens where surface 3 was made of BK7, and surface 4 was made of F2, and surface 5 was air. The nominal thicknesses are 3, 4, and 6 mm, respectively. If a TTHI operand was defined by the default tolerance algorithm for surface 3, an adjustment would be defined for surface 5. If the tolerance value was +.1 

mm, then during analysis the thicknesses would be changed to 3.1, 4.0, and 5.9, respectively. Thus, the absolute positions of surfaces 6 through the image surface are unaffected by the change in thickness on surface 3.

In your particular case, you would defined your TTHI operands as such:

And Thickness 5 will adjust to “absorb” the thickness difference created by the tolerances.

Since you are new to tolerancing, you may want to have a read at this article, and this other article, which also describes the use of compensators. In some cases, the last thickness of a system can be adjusted experimentally to achieve the bests focus despite the tolerances, and this is what a compensator would do during tolerancing.

I hope this helps, and take care,

David