At age 40, most of us can read something 10 inches away. By age 50, that distance is usually closer to 16 inches and it increases as you get older. This condition, called presbyopia, is caused by the eye loosing its ability to focus and approximately 90 million Americans suffer from it.
When you consider this and other eye conditions that affect vision, you can understand how essential it is for publishers to choose fonts with great care. This doesn’t apply just to the interior of the book, but to the title, back cover text, online ads, websites, posters and any printed matter that will be used in promoting your books.
Here’s a little trick that will test the legibility of your font under less than ideal circumstances: just set a few lines and blur the text in Photoshop or similar software. Do letters such as a, o and d fill in? Do tall letters like i and t and l look alike? Are the letters so close together they’re just one big blur? Do narrow parts of the glyph (glyphs are the letters, numbers, punctuation marks, etc.. that we use to write with) vanish all together?
Paying close attention to the height difference in letters, the spacing between letters and worlds and the thickness of each stroke that makes up a glyph
Deep leading (space between the lines) aids legibility. Generally, 1.5 to 2 times the space between the words is sufficient. This can vary depending on the typeface.
For larger printed matter like posters, The Americans with Disabilities Act suggests height and weight ratios for signage should be between 60% and 100% of the height and that each stroke weight should be between 10% and 20% of the height.
Some fonts that fit this criteria include: Futura, Futura Condensed Bold, Futura Book, (but not Futura Light, condensed or bold), Frutiger Light, Frutiger, Frutiger Bold, Gill Sans, Gill Sans Bold (but not Gill Sans Light) Otpima, Bodoni, Bodini Book. Century Schoolbook, (not Century Schoolbook Bold) Garamond, Garamond Semibold, (but not Garamond Bold), Palatino and Palatino Bold.
Remember, no one is going to struggle to read your message.