How to change greek letters in MathPTMX package to default font?

Question

I really like the greek letters of the default LaTeX font but I want the rest of the characters to be in Times New Roman using the Mathptmx font. I find the greek letters of the mathptmx package rather ugly since they're disproportionately bolder than the usual text.

So may I know how can I change the greek characters only and retain the times new roman text? I have tried many suggestions from countless websites but to no avail. Alternatively, can I ask if there's a way to change the greek letters somewhat more similar to the greek letters in the books like those in University Physics by Young and Freedman?

Answer 1

First of all, as David Carlisle pointed out in the comments, if you want to use a Times clone it would be better to use the more recent newtx bundle than mathptmx, which is now obsolete.

Now, to strictly answer your question, after loading mathptmx you can redeclare all greek letters in the Computer Modern font (which is the default font). This will work just as well if newtx is loaded instead of mathptmx, by the way. Here's a complete example.

\documentclass{article}
\usepackage{amsmath}
\usepackage{mathptmx}
\DeclareSymbolFont{cmletters}{OML}{cmm}{m}{it}
\DeclareMathSymbol{\Gamma}{\mathalpha}{cmletters}{0}
\DeclareMathSymbol{\Delta}{\mathalpha}{cmletters}{1}
\DeclareMathSymbol{\Theta}{\mathalpha}{cmletters}{2}
\DeclareMathSymbol{\Lambda}{\mathalpha}{cmletters}{3}
\DeclareMathSymbol{\Xi}{\mathalpha}{cmletters}{4}
\DeclareMathSymbol{\Pi}{\mathalpha}{cmletters}{5}
\DeclareMathSymbol{\Sigma}{\mathalpha}{cmletters}{6}
\DeclareMathSymbol{\Upsilon}{\mathalpha}{cmletters}{7}
\DeclareMathSymbol{\Phi}{\mathalpha}{cmletters}{8}
\DeclareMathSymbol{\Psi}{\mathalpha}{cmletters}{9}
\DeclareMathSymbol{\Omega}{\mathalpha}{cmletters}{10}
\DeclareMathSymbol{\alpha}{\mathord}{cmletters}{11}
\DeclareMathSymbol{\beta}{\mathord}{cmletters}{12}
\DeclareMathSymbol{\gamma}{\mathord}{cmletters}{13}
\DeclareMathSymbol{\delta}{\mathord}{cmletters}{14}
\DeclareMathSymbol{\epsilon}{\mathord}{cmletters}{15}
\DeclareMathSymbol{\zeta}{\mathord}{cmletters}{16}
\DeclareMathSymbol{\eta}{\mathord}{cmletters}{17}
\DeclareMathSymbol{\theta}{\mathord}{cmletters}{18}
\DeclareMathSymbol{\iota}{\mathord}{cmletters}{19}
\DeclareMathSymbol{\kappa}{\mathord}{cmletters}{20}
\DeclareMathSymbol{\lambda}{\mathord}{letters}{21}
\DeclareMathSymbol{\mu}{\mathord}{cmletters}{22}
\DeclareMathSymbol{\nu}{\mathord}{cmletters}{23}
\DeclareMathSymbol{\xi}{\mathord}{cmletters}{24}
\DeclareMathSymbol{\pi}{\mathord}{cmletters}{25}
\DeclareMathSymbol{\rho}{\mathord}{cmletters}{26}
\DeclareMathSymbol{\sigma}{\mathord}{cmletters}{27}
\DeclareMathSymbol{\tau}{\mathord}{cmletters}{28}
\DeclareMathSymbol{\upsilon}{\mathord}{cmletters}{29}
\DeclareMathSymbol{\phi}{\mathord}{cmletters}{30}
\DeclareMathSymbol{\chi}{\mathord}{cmletters}{31}
\DeclareMathSymbol{\psi}{\mathord}{cmletters}{32}
\DeclareMathSymbol{\omega}{\mathord}{cmletters}{33}
\DeclareMathSymbol{\varepsilon}{\mathord}{cmletters}{34}
\DeclareMathSymbol{\vartheta}{\mathord}{cmletters}{35}
\DeclareMathSymbol{\varpi}{\mathord}{cmletters}{36}
\DeclareMathSymbol{\varrho}{\mathord}{cmletters}{37}
\DeclareMathSymbol{\varsigma}{\mathord}{cmletters}{38}
\DeclareMathSymbol{\varphi}{\mathord}{cmletters}{39}
\begin{document}
\begin{gather*}
\sin^2(\theta) + \cos^2(\theta) = 1 \\
\alpha + \beta + \pi
\end{gather*}
\end{document}

---

Since you mention in the question that the reason you wish to change the greek letters is that they seem too bold compared to the rest of the text, I thought it would be relevant to point out that the weight of the letters from newtx is certainly more balanced than that of the letters from mathptmx. Here's how it looks with only newtx.

\documentclass{article}
\usepackage{newtx}
\begin{document}
\begin{gather*}
\sin^2(\theta) + \cos^2(\theta) = 1 \\
\alpha + \beta + \pi
\end{gather*}
\end{document}