\startsetups test
  \midaligned{(\fontclass)}
  \blank
  \startformula
  % op:\the\Umathoperatorsize   \textstyle
  % fr:\the\Umathfractiondelsize\textstyle
    \textstyle\left(\frac{1}{2}\right)
    \tbinom{1}{2}
  \stopformula
  \blank
  \startformula
  % op:\the\Umathoperatorsize   \displaystyle
  % fr:\the\Umathfractiondelsize\displaystyle
    \displaystyle\left(\frac{1}{2}\right)
    \dbinom{1}{2}
  \stopformula
  \blank[2*big]
\stopsetups

\starttext

    {\setupbodyfont[cambria]  \setup[test]}
    {\setupbodyfont[modern]   \setup[test]}
    {\setupbodyfont[palatino] \setup[test]}
    {\setupbodyfont[lucida]   \setup[test]}
    {\setupbodyfont[lucidaot] \setup[test]}

\stoptext
