Amsmath's \binom looking weird

Question

Using the MWE

\documentclass[fontsize=8pt, a4paper, DIV12]{scrbook}

\usepackage{amsmath}

\begin{document}
\[ e^t = x^{(5)} - 2x^{(3)} + \dot{x}
 = \sum_{k = 0}^{5} \binom{5}{k} p^{(k)}(t) e^t
 -2\sum_{k = 0}^{3} \binom{3}{k} p^{(k)}(t) e^t
 + \sum_{k = 0}^{1} \binom{1}{k} p^{(k)}(t) e^t
\]
\end{document}

I get the output

with strange looking binomial coefficients. Root cause is the font size.

Is there any way to get the usual look without changing font size?

Answer 1

If you use the \mbinom command, from the nccmath package (medium-sized \binom, ~80 % of display style), it looks much better, in my opinion:

\documentclass[fontsize=8pt, a4paper, DIV12]{scrbook}

\usepackage{amsmath, nccmath}

\begin{document}

\[ e^t = x^{(5)} - 2x^{(3)} + \dot{x}
 = ∑_{k = 0}⁵ \mbinom{5}{k} p^{(k)}(t) e^t
 -2∑_{k = 0}³ \mbinom{3}{k} p^{(k)}(t) e^t
 + ∑_{k = 0}¹ \mbinom{1}{k} p^{(k)}(t) e^t
\]

\end{document}