Difference in Cyrillic font series

Question

I would appreciate if someone could help me in solving a "font puzzle". I am trying different ways to typeset a text in cyrillic.

First example of code, compiled with pdfLaTeX:

\documentclass[14pt]{extreport}
\usepackage[T2A]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[russian]{babel}
%--------------------------------------
\begin{document}
    Еще недавно ему часто
\end{document}

Second example of code, compiled with LuaLaTeX:

\documentclass[14pt]{extreport}
\usepackage{fontspec}
\usepackage{polyglossia}
\usepackage{unicode-math}
\setmainlanguage{russian}
\setmainfont{CMU Serif}
%------------------------
\begin{document}
    Еще недавно ему часто
\end{document}

The output can be seen below:

The second fragment of code produces somewhat "thicker" type of font, whereas the first fragment, compiled with pdfLaTeX, gives a "thinner", more elegant letters(seen below in the picture).

My questions: 1) what are reasons for this difference? 2) Is it possible to obtain same "thin" font, albeit with LuaLaTeX-suitable code?

Answer 1

An image is worth a thousand words

What's the meaning of the image?

It's a tabular; the first column has a description, the second column images produces by the files described below.

The source is

\documentclass{article}
\usepackage{graphicx}

\begin{document}

\begin{tabular}{@{}ll@{}}
Optical: & \raisebox{-3pt}{\includegraphics{testcyro.pdf}} \\[3pt]
Scaled: & \raisebox{-3pt}{\includegraphics{testcyrs.pdf}} \\[3pt]
CMU: & \raisebox{-3pt}{\includegraphics{testcyru.pdf}}
\end{tabular}

\end{document}

In the “optical” line, the font used is larm1440, which is not just the font at 10pt scaled by 14.4% like in the “scaled” line.

Note that the “CMU” line is the same as the “scaled” line.

Optical sizes are not the same as scaling. CMU Serif is only available at 10pt design, the other sizes are obtained by scaling; conversely, larm is available at several optical sizes. The answer to your second question is no, I'm afraid: there's no free OpenType Cyrillic font supporting optical sizes, as far as I know.

The codes

testcyro.tex

\documentclass{standalone}
\usepackage[T2A]{fontenc}
\usepackage[utf8]{inputenc}
\begin{document}

\fontsize{14}{14}\selectfont
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\end{document}

testcyrs.tex

\documentclass{standalone}
\usepackage[T2A]{fontenc}
\usepackage[utf8]{inputenc}
\begin{document}

\font\test=larm1000 at 14pt \test

Еще недавно ему часто

\end{document}

testcyru.tex

\documentclass{standalone}
\usepackage{fontspec}
\setmainfont{CMU Serif}

\begin{document}

\fontsize{14}{14}\selectfont
Еще недавно ему часто

\end{document}