This definitely depends on the typeface. What type will you use?

I don't have a preference for typeface. It can be any typeface as long as it holds up at tiny sizes.

Down to 3,5 pt with La Formica.
I can get you in contact with the designer.

May I ask how you got to that size?

This is a size you can still read without a magnifying glass. So, with that typeface you could possibly go down to 1 pt if you’re giving out the glasses.

I can't give you a number, but I will point out that if I could it would be rather different from other people's answers due to my failing eyesight. I think you'll find that those who already need magnification to read normal book text are probably going to be disinclined to give your project the scrutiny you desire, which means you're excluding a potentially large audience.

André

Bell Gothic prints out well at 3pt on a HP Laserjet, at 2pt you can read it but letters break up - at 3 they are clear and connected.

Thanks for all of your answers. Nobody has mentioned DPI yet. Is everyone making an assumption on the DPI? I may be missing out on something significant, but is everyone assuming a DPI of 300? Aren't there commercial book printers who can print at higher DPI than 300? And with DPI of over 300, aren't you able to theoretically print at a smaller size?

There are modular fonts (esp from the era when Flash ruled on the web) based on grids down to 3 by 5 pixels. Assuming you need at least a pixel between lines you could print 423 lines of text per inch (on a 2450 dpi printer — a common resolution in high end equipment). An ordinary magnifying glass would be of little use — you’d need a microscope.

If you want people to only be able to read it with a magnifying glass, the two things you need to nail down are mechanical: the dpi of the printer and the magnification factor of the glass; one will impose a lower limit than the other, and that's what you'd have to shoot for.

hhp

And, of course, you need to consider the actual resolution of the output, not the theoretical DPI: the interaction between ink and surface will play a major role.

True, the paper can make a big difference. Plus printer manufacturers do often lie.

hhp

Note that at sizes smaller than -- guestimating here -- around 4 pts some additional factors come into play: the roughness of the paper, and the thickness of the ink or toner. Even with super-smooth paper, ink may spread out (the same problem as when trying to accurately produce an exact level of gray, where it is called "dot gain") and toner may not be delineated sharply.

Once, while retouching small faults in a bitmap image -- which, by all rights, should have reproduced faithfully -- I inserted my initials in it with 5 pixel high characters into the dot of an 'i'. Unfortunately, after offset printing, the ink had run ever so slightly. The dot was visibly not 'sharp' anymore, but that was about it.

- http://www.all-the-worlds-a-page.com
- http://www.wired.com/2013/07/this-poster-has-820000-words-on-it-you-can-...

Would pixel fonts work? Some are very tiny.

Printing on coated paper (like most magazines are printed on) will create less ink spread.

Best results might be type imaged directly on photographic paper by a professional typesetter, but many are out of business due to desktop publishing and digital files.

Keep in mind that legibility will vary from person to person. Eyesight generally gets worse as we get older.

I inserted my initials in it with 5 pixel high characters

Hah, I like doing that too! Although in print I've only done it once.

hhp

Typonaut wrote:

Nobody has mentioned DPI yet. Is everyone making an assumption on the DPI? I may be missing out on something significant, but is everyone assuming a DPI of 300? Aren't there commercial book printers who can print at higher DPI than 300?

There are very few printers that output at resolutions of 300 dpi. I think you're confusing the 300 ppi that's a common resolution of photos and scanned imagery intended for printing at about 150 lpi.

Type is typically vector-based, so resolution is irrelevant. Unless the typography is printed with a screen tint, the 150 lpi is also irrelevant.

What is relevant is the resolution of the output device. An inexpensive B&W laser printer typically prints at least at 600 dpi. The output resolution of a typical commercial-quality imagesetter or platesetter typically varies between 1200 and 4800 dpi. The resolution of microprinting used for anti-counterfeiting purposes on currency is even higher than that.

A HP Laserjet, as mentioned in my post above, prints at 600 or 1200 dpi.

Since you need to be able to give the magnifying glasses away, that lets out using a Scanning Tunneling Electron Microscope for the instrument of magnification... looking into microfilm, microfiche, and "microcard", as well, shows that the lower limit is rather vague. Microprinting as a security feature on currency is another thing to examine (ah, that's been mentioned).

With even a 300 dpi laser printer, one can go rather small - on a good one, one could actually read text in a 5x7 dot matrix style.

And a while back I had been seeing ads for a version of Ian Fleming's novel Casino Royale in small printing that was a poster you could put on your wall.

Thanks everyone. You've all been great!

I have a much better understanding now for what the font size can be.

You might wan to check Minuscule out and other suggestions here:
http://typophile.com/node/36897

Interesting previous thread http://typophile.com/node/7941 which chose Meta, Bell Gothic, Galfra, Clottes, Nomina, Asphalt, Bell Centennial, Retina, Yellow, Adsans, Colorado, Delia, Amplitude, Rialto Pressa
Another previous thread http://typophile.com/node/83492
The fonts designed for tiny printing, size agate and below, often have relatively huge ink traps and look truly strange when magnified.
One of the places where printers pushed the size of fonts to the tiny is telephone directories. See some comments on Luc Devroye's phone page http://luc.devroye.org/phone.html
Also http://www.martinmajoor.com/2.2_telefont_article_eye.html
And on the magnifying glass issue http://pressf1.pcworld.co.nz/showthread.php?124832-Small-font-in-new-tel...
Other places where printing is too small for reasonable reading, even with a magnifying glass are the credits on DVD covers and the leaflets of legalese sometimes stuffed in product packages. What's the point of printing it if almost no one can read it?
Don

That what the idea of "small print" is all about Don - they do not want people to read it.

If you want the highest resolution, don't use a home or office printer. Professional printers have far better equipment.

And if this is acceptable output, professional typesetting directly on photographic paper can have a resolution of around 2,500 dots per inch, depending on the equipment used.

The resolution of a professional Imagesetter is typically between 1200 and 4800 dpi. Can be to photo paper or film.