I bought the Kindle edition, I was initially a little concerned as not all Kindle books read well. This version is great, all images are present and is semi searchable.
I bought the book as I was about to spend some serious money on some eye pieces, this was money well spent and I bought knowingly.
It is a technical book and there is some maths to absorb as well as a bit of physics and optics. But the effort is well worth it.
The historical development of the lens types is well dealt with and a good read on its own. The considerations raised about lens types are also very good. The author speaks well about the pluses and minuses of lens designs, so well that I might even consider using a Kellner in the right situation.
The final section on the makers and types of lenses both current and no longer produced makes this book even more useful, especially if you happen to be looking at second hand lenses that are no longer in production.