How to choose good values for findent and nindent?

Question

I'm using the lettrine package with the default two-line initials (so that I can use findent and nindent). My problem is typographical rather than TeXnical: how do I choose good values for these parameters? Of course, one has to take the shape of the letter into account, but the case especially tricky for me is when the first word is an "I" (the text is in English). What value for findent (the space between the "I" and the next word would you suggest? More importantly, should I set the next line closer or farther to the initial? (I guess closer is better - but by how much?) I'm using Linux Libertine, in case anyone's wondering, but I wouldn't expect the "right" values to vary very much with the font.

In the answers, I'd be most pleased if you not only gave some suggested answers to these two particular problems, but also some general hints about how to wisely choose these values. (Perhaps turning this question into cw is a good idea?)

Answer 1

Not really an answer, but a follow-up to Yannis' answer: here is how I might typeset his examples using XeLaTeX (and the EB Garamond fonts). I would let the serifs and a bit of the rounded O lhang in the left margin a bit for better optical alignment. I also like the first word to be tightly spaced (findent) but to have more space before the second line (nindent). For rounded or curved letters I add a negative slope to make the text track the outline of the letter (but maybe this looks too fussy?). I also increase the size of the letters a bit loversize so they optically extend up to the height of capital letters. (In particular, I do not like how the "O" in Yannis example only comes up to the height of the "n".)

Interesting problem of how to automate all of this.

\documentclass{book}
\usepackage{fontspec}
\setlength\textwidth{4in}
\setmainfont{EB Garamond}

\usepackage{lettrine}
% Need to specify a config file to use \LettrineOptionsFor, even if it is
% not used.
\renewcommand{\DefaultOptionsFile}{NoFileOnPurposeHack.cfg}

\LettrineOptionsFor{I}{
  loversize=0.09,    % Slightly larger to extend up to cap height
  findent=0pt,       % No indent for first line for word "in"
  nindent=0.25em,    % Indent second line (no "ibook"'s here)
  lhang=0.2}         % Hang serifs into the margin for optical alignment
\LettrineOptionsFor{O}{
  loversize=0.08,    % Slightly larger to extend up to cap height
  lraise=-0.01,      % Lower slightly for optical alignment
  findent=-0.2em,    % Negative indent to make "On" like a word
  nindent=0.4em,     % Indent second line (partially cancel negative indent)
  slope=-0.25em,     % Bring third line back a bit (maybe too fussy?)
  lhang=0.1}         % Hang it out for optical alignment

\begin{document}
\lettrine[lines=2]{I}{}t is a pleasure to record my thanks to the people who
contributed to this book.  The indelible traces of wonderful teachers and
friends are imprinted on each page, and the existence of this project is
unimaginable to me without their help.

\vspace{2\baselineskip} 

\lettrine[lines=3]{O}{}n 19 July 1925 Druze farmers shot down a French
surveillance airplane circling above their mountain home, Jabal
\d{H}awr\^an, some 1000 kilometers south of Damascus.\textsuperscript{1}
These ere the first shots of a revolt that would last two years, beginning
and ending in Jabal \d{H}awr\^an.
\end{document}

There are also some nice examples of drop caps on typophile, but all the examples are much more extreme to the extent that they completely skirt the issue. You might find some expert advice about the typographic aspects there though.

Answer 2

The distance between the drop cap and the indented text is normally as you noted very small approaching almost the normal distance between the letters (i.e., as if you have typed the letters normally). This is probably why the lettrine package author has set the value of findent=0pt. The images below are from a book I happened to been reading this afternoon. As you will observe the "I" is very close to the text.

The distance is kept constant for almost all letters although for the O is approximately 1pt wider, but then the "O" is three lines high whereas the "I" was set on only two.