I would like to have two macros that mimic \left( and \right), but limits the size of the parenthesis to \Bigl( and \Bigr) (allows smaller sizes), respectively. In the below MWE, one needs to extend two \newcommand lines. I am aware that this might be a difficult task, since you need to know the height of the object that you are enclosing.
MWE
\documentclass{article}
\newcommand{\leftc}[1]{ \left#1 }
\newcommand{\rightc}[1]{ \right#1 }
\begin{document}%
\begin{equation}%
\left( a/b \right), ~ \left( \prod_{i = 1}^{100} \right), ~ \Bigl( \prod_{i = 1}^{100} \Bigr)
\end{equation}%
\begin{equation}%
\leftc( a/b \rightc), ~ \leftc( \prod_{i = 1}^{100} \rightc), ~ \Bigl( \prod_{i = 1}^{100} \Bigr)
\end{equation}%
\end{document}%
Output of MWE
Desired output



\leftand\rightwhich adds unwanted horizontal space and other effects. certainly I'd never use it here:\left( a/b \right)– David Carlisle Jan 04 '16 at 15:07\left( a/b \right); this was done purely for demonstrative purposes. I have a different\newcommand, say\E, that uses\left(and\right)but sometimes creates parentheses that I feel are too large. So I would like to simply substitute\leftc(and\rightc)for the\left(and\right)in the definition of\E. – Ritz Jan 04 '16 at 15:16