title: Changing the font size of figure captions in RMarkdown pdf output
body: <p>I would like to make the font size of all captions (figures and tables) in my R Markdown document smaller. I'm using bookdown. The final output is pdf and I'm working in R Studio. To load the picture, I use the <code>include_graphics</code> function from <code>knitr</code>, because I've been told it's the best way (see <a href="http://www.zevross.com/blog/2017/06/19/tips-and-tricks-for-working-with-images-and-figures-in-r-markdown-documents/#default-settings-for-including-images-and-figures-in-r-markdown" rel="noreferrer">here</a>).</p>
  
  <p>I only found the exact same question, but for html output <a href="https://stackoverflow.com/questions/45018397/changing-the-font-size-of-figure-captions-in-rmarkdown-html-output/45022100#45022100">here</a></p>
  
  <p>An example <code>.rmd</code>:</p>
  
  <pre><code>---
  output: pdf_document
  ---
  
  Normal text has the same size as the captions.
  
  ```{r, echo = FALSE, out.width = '50%', fig.cap = "The caption has the same size as normal text."}
  knitr::include_graphics('logo.png')
  ```
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/23hqg.png" rel="noreferrer"><img src="https://i.stack.imgur.com/23hqg.png" alt=" "></a></p>
  
  <p>As you can see, the caption font size and the regular text font size are <em>exactly</em> the same, which doesn't look that nice. How can I solve this problem?</p>