Changing Math-Font-Size with DeclareMathSizes

Question

I am thrilled that \DeclareMathSizes gives such nuanced control over the sizes of the different parts of the equations. Experimenting with the mt-size, s-size and ss-size paramters.

Here's another one with change of paramters:

At this point I noticed that \Sigma and \Pi always remain the same size. How can they also be changed?

---

\documentclass[12pt]{article}
%Gummi|065|=)
\usepackage{lmodern}
\usepackage{amsmath, amsfonts, amssymb}
\usepackage[landscape, margin=0.5in]{geometry}

\DeclareMathSizes{20}{20}{25}{10}

\begin{document}

\fontfamily{qag}\selectfont \fontsize{20}{30}\selectfont

\noindent modular properties of $\theta = \sum q^{n^2}$ and  
$\eta =  q^{1/24} \prod (1 - q^n)$

\end{document}

---

How can I control the size of my summation and product operators Σ and Π ?

Answer 1

There are two problems:

1. TeX Gyre Adventor has a bigger x-height than Computer Modern
2. lmodern loads the math extension font at a fixed size

The second problem is the same as described in Problems using lmodern with very small font sizes. Just removing lmodern will solve it as well.

\documentclass[12pt]{article}
\usepackage{amsmath,amssymb}
\usepackage[landscape, margin=0.5in]{geometry}

\DeclareMathSizes{20}{25}{21}{17}

\begin{document}

\fontfamily{qag}\fontsize{20}{30}\selectfont

\noindent modular properties of $\theta = \sum q^{n^2}$ and
$\eta =  q^{1/24} \prod (1 - q^n)$

\end{document}