Change kerning for `f'` in math mode

Question

I want to adjust the kerning between f' in math mode (and other pairs) across the entire document. I found https://tex.stackexchange.com/a/219881/54601, which is exactly what I want but for text mode, and indeed it does not work for math mode. How do I do it? I do not want to have to create a macro for every pair. I would like to use XeTeX if possible. Is it? I have already gone through like a hundred different questions on TeX SE and I could not find an answer to my question.

Here is an example that needs fixing. No, I do not want to use any other font, and no, I do not want to fix each instance manually nor use a macro. Is LaTeX or XeTeX is incapable of fixing such a simple typographical issue?

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{xits-math.otf}
\setmathfont[range=\mathit]{Times New Roman Italic}
\begin{document}
$f'$
\end{document} 

Answer 1

(Too long for a comment, hence posted as an answer of sorts.)

I assume you're using a Windows-based computer. When I compile your MWE under Windows 7 and MikTeX 2.9, I get exactly the problem that you report in your posting. That's why I'm guessing you're on a Windows-based system.

Now: Is there any chance at all that you could switch to a Mac to compile your document? The reason I ask is that Times New Roman Italics under MacOSX 10.10.4 "Yosemite" does have the required kerning information stored in the font tables. To wit, when I compile your test program, under either XeLaTeX or LuaLaTeX, on a system that runs MacOSX 10.10.4 "Yosemite" and MacTeX2015, I get the following output:

No kerning adjustment would appear to be necessary, right?

---

Addendum to address your follow-up comment: $VWab$, $\dfrac{2\pi ft}{k}$ is rendered as follows:

I don't know about your aesthetics, but I'd say that's pretty nice. :-)

\documentclass[border=1pt]{standalone}
\usepackage{amsmath,unicode-math}
\setmathfont{XITS Math}
\setmathfont[range=\mathit]{Times New Roman Italic}
\begin{document}
$VWab$, $\dfrac{2\pi ft}{k}$
\end{document} 

Answer 2

I had the same problem using \setmathfont. Here is a minimal working example exhibiting problem and solution (using f\prime instead of f'):

\documentclass[fontsize=30pt]{scrartcl}
\usepackage{unicode-math}
\setmathfont{Latin Modern Math}
\begin{document}
\[ f'\,a'\quad f\prime\,a\prime \]
\end{document}

Here is the output, compiled by TeX Live 2013's xelatex on Ubuntu linux:

Interestingly, using a smaller font size mitigated the problem.

When not using \setmathfont to set a custom math font, the problem didn't occur.

Answer 3

Well, in lieu of fixing the font, we can simply redefine \prime to insert \mskip1mu before it. I don't know why it didn't occur to me previously.