[alfordsteven]

Greetings:
The unfortunate issue about PDFs on the Kindle is that they are often unreadable owing to the tiny text, and the zoom Kindle provides only enlarges a certain portion of text. I was delighted with my first Calibre conversion from PDF to MOBI since, after the transfer to the 3Gen Kindle (on Mac OSX 1.6) the text was not only readable, but scalable.
Since then I have tried with several more PDFs and have had the disheartening experience of seeing, once again, tiny, unreadable, unscalable text, only this time in the MOBI format. I tried changing "base font size" in the conversion window, but to no effect: the text looks like a jpg on the Kindle and, without laser contacts, remains unreadable on the Kindle.
Since the conversion worked once, I am unsure if that was a happy accident, or if I'm doing something wrong. The PDFs originate at JSTOR, an academic web site and don't seem to be unusual in any way.
Please help. My thanks in advance.

Steve