Subfloat indexes misaligned when using setcaptionwidth

Question

I have the following document:

\documentclass{article}
\usepackage{subfig}
\usepackage{graphicx}
\usepackage{geometry}
\setcaptionwidth{12cm}
\begin{document}
\begin{figure}[t]
  \centering%
  \subfloat[]{\label{figa}\includegraphics[width=38mm,%
    height=32.48mm]{fig1}}\hspace{3mm}%
  \subfloat[]{\label{figb}\includegraphics[width=38mm,%
    height=32.48mm]{fig2}}\hspace{3mm}%
  \subfloat[]{\label{figc}\includegraphics[width=38mm,%
    height=32.48mm]{fig3}}%
  \caption{Some caption.}
  \label{fig-moire-comp-xue}
\end{figure}
\end{document}

I want the captions of all figures to have a width of 12cm (slightly less than main body text), and have TeX generate the (a), (b) labels for me.

This is the result:

If I then comment out the line in the preamble setting the caption width to 12cm, it aligns as I want:

(This is an issue in my thesis, a much more complicated document, but I think I have narrowed it down to this conflict.) I just want the alignment to be fixed, but still have 12cm wide captions for all figures.

I don't really care if the solution is an ugly per-figure hack, I just care about alignment.

Thanks for any help.

Answer 1

You can set globally the caption's width and separately the subcaption's width:

\captionsetup{width=12cm}
\captionsetup[subfloat]{margin=0pt}

Don't use \setcaptionwidth, of course (it is an obsolete command of caption version 2).w

Answer 2

set the captionwidth before the caption itself:

\documentclass{article}
\usepackage{subfig}
\usepackage[demo]{graphicx}
\usepackage{geometry}
\begin{document}
\begin{figure}
  \centering%
  \subfloat[]{\label{figa}\includegraphics[width=38mm,%
    height=32.48mm]{fig1}}\hspace{3mm}%
  \subfloat[]{\label{figb}\includegraphics[width=38mm,%
    height=32.48mm]{fig2}}\hspace{3mm}%
  \subfloat[]{\label{figc}\includegraphics[width=38mm,%
    height=32.48mm]{fig3}}%
  \setcaptionwidth{12cm}
  \caption{Some very long caption to show that is not
           wider than 12 cm as defined by the setting.}
  \label{fig-moire-comp-xue}
\end{figure}
\end{document}