Different results of \mag statement

Question

The following example gives different results for pdfLaTeX and LuaLaTeX. I use a recent TeX Live 2019 installation.

\documentclass[a4paper]{article}
\usepackage{geometry}
\mag=250 %
\setlength\parindent{0pt}
\begin{document}
\Huge
\LaTeX \hfill \LaTeX
\vfill
\LaTeX \hfill \LaTeX
\end{document}

1. pdfLaTeX: A page on A8 paper (53mm x 74mm)

2. LuaLaTeX: A page on A4 paper (210mm x 297mm)

I use the package »geometry« only for transfering the page size informations to the output file. Without »geometry« I get the same results. Why ist the size not changed with LuaLaTeX? Can anyone enlighten me? Thanks in advance.

Answer 1

This is a documentated difference to pdftex. From the manual:

Magnification (\mag) is only supported in dvi output mode. You can set this parameter and it even works with true units till you switch to pdf output mode. When you use pdf output you can best not touch the \mag variable. This fuzzy behaviour is not much different from using pdf backend related functionality while eventually dvi output is required