Reducing caption font size

Question

I would like to see the caption font (and caption label too) with size that is smaller than in whole document.

I`ve tried some solutions from SE (Font size of Figure Caption Header), e.g.:

\usepackage[font=small]{caption}

and

\usepackage{caption}
...
\captionsetup[figure]{font=small}

but is doesn`t work in my case.

I think it may be caused by one of this conditions or both:

1. I`m using extarticle document class (because I need 14pt text size);
2. I have the following lines in my code (that centering captions of figures):

\makeatletter
\long\def\@makecaption#1#2{%
  \vskip\abovecaptionskip
  \hbox to\textwidth{\hfill\parbox{1\textwidth}{\begin{center}#1: #2\end{center}}\hfill}
  \vskip\belowcaptionskip}
\makeatother

Can you give me some advices about my problem? In addition, how can I manually derive caption font size (for example 12pt or 13pt)?

Update. here is the MWE of my problem (I hope it`s actualy "M"inimal):

\documentclass[14pt,a4paper]{extarticle}

\usepackage{graphicx}
\graphicspath{ {pictures/} }

\makeatletter
\long\def\@makecaption#1#2{%
  \vskip\abovecaptionskip
  \hbox to\textwidth{\hfill\parbox{1\textwidth}{\begin{center}#1: #2\end{center}}\hfill}
  \vskip\belowcaptionskip}
\makeatother

\begin{document}

Picture:
\begin{figure}[ht]
   \includegraphics[width=0.5\linewidth]{levels.png}
    \caption{Here is a big picture. Caption are centered but it has the same font size as in whole document.}
\end{figure}

\end{document}

Answer 1

Since you're already redefining \@makecaption, you can set the size there (and that's likely why you're finding that the caption package isn't working as expected).

I'd also note that your definition can be improved a bit. The nested \hbox to\textwidth and \parbox are redundant and you can actually get rid of both. You probably want to also not use the center environment as that adds a bit of vertical space above and below since it's implemented using a trivlist.

Instead I would do this:

\makeatletter
\long\def\@makecaption#1#2{%
  \vskip\abovecaptionskip
  {
   \centering
   \small % or whatever your desired size is
   #1: #2
   \par % otherwise the centering will go away before it gets applied to the caption
  }
  \vskip\belowcaptionskip}
\makeatother