`\begin{table}
\centering
\caption{Distanze focali.}
\label{tab:Distanze_focali}
\begin{tabularx}{12cm}{XXX}
\toprule
\multicolumn{3}{c}{\textbf{\boldmath$200$ mm}} \\
\midrule
\boldmath$p-q$ & \boldmath$f$ & \boldmath$f\%$ \\
\midrule
1,0 cm & 193,5 mm & 96,7 \% \\
66 cm & 197 mm & 98 \% \\
59,2 cm & 195,3 mm & 97,7 \% \\
\midrule
\multicolumn{3}{c}{\textbf{\boldmath$150$ mm}} \\
\midrule
\boldmath$p-q$ & \boldmath$f$ & \boldmath$f\%$ \\
\midrule
32 cm & 144 mm & 96 \% \\
42,4 cm & 147,0 mm & 98,0 \% \\
15 cm & 144 mm & 96 \% \\
\midrule
\multicolumn{3}{c}{\textbf{\boldmath$100$ mm}} \\
\midrule
\boldmath$p-q$ & \boldmath$f$ & \boldmath$f\%$ \\
\midrule
94 cm & 100 mm & 100 \% \\
88,4 cm & 97,4 mm & 97,4 \% \\
29,2 cm & 95,5 mm & 95,5 \% \\
\bottomrule
\end{tabularx}
\end{table}`
io la avevo fatta cosi…