Hello everyone,

I was working on tolerancing a new design and comparing “old method” TFRN+ TIRR, to the ‘new method’ ISOA/ISOB/ISOC, and it seemed to me that the new method was more ‘pessimistic’ that the old one.

Looking in details to compare the methods, I made a very simple system (1 PCX lens, R=50mm, N-BK7, Aperture 10mm) and compared different combinations :

• ISOC alone
• TIRR + ISOC
• ISOB + ISOC

Looking at the results I stumbled upon the fact that the contribution in sensitivty of ISOC was not the same depending of the associated operand :

ISOC alone : ISOC       2                 -0,50000000         0,00399992         0,00215149         0,50000000         0,00399992         0,00215149

TIRR + ISOC : ISOC       2                 -0,50000000         0,00399992         0,00215149         0,50000000         0,00399992         0,00215149

ISOB+ISOC : ISOC       2                 -0,45000000         0,00790629         0,00605786         0,45000000         0,00790629         0,00605786

(Here I reduced the value to 0.45 to be compatible with ISOB)

The two first methods give similar result, which is correct to me as in sensitivity mode, only this operand is applied to the surface, and with the same amplitude, one get the same impact on performances.

But it is not the case with ISOB+ISOC, with a ratio of around 3, which bothers me.

Does anyone have some explanation ?

I am with OpticsStudio Pro 2026R1.