Some fonts come with different optical sizes. A few Adobe fonts have different optical sizes that are recommended for 6–8 point text, 9–14 point, 14–24, and 24+ points. I am designing an A1 poster, which is will not be read from such close a distance as regular text. Most, if not all, text will be set larger than 24 points, and certainly not smaller than 14. Should I use the optical sizes as intended, or should I take the viewing distance into account?

Example: 12pt type viewed from 0.4m subtends an angle of 0.61 degrees, so it looks as tall as 30pt type viewed from 1m distance, which also subtends an angle of 0.61 degrees. If I use 30pt type on the poster, should I use the optical size intended for 24+ points, or the size intended for 9–14 points?


"Should" is too strong a word. If you see value in it, do it. The Adobe page kind of begs the question by merely asserting the use of "optical size" is correct.

I think the descriptions on their site regarding where each type of face is appropriate heavily implies a specific reading distance and your way of translating that is sound: 12pt > .61 > 30pt.

If you want to properly evaluate the typefaces in the context of the design, you will need to either reduce in scale when going to hardcopy or print 100% and step back.

Optical sizing was a concession to technology.

The reason why the display type has more refinement is because "they" thought the detail would actually grab ink and hold at the larger conceived sizes.

Additionally, they had to mold and cast these from lead etc. rapidly and again, too much detail can increase manufacturing waste.

I am reminded of a literal old wives tale about the woman who cuts the ends off a roast and when asked why it is because her mother did it and the roast was always good. They go back and ask the mother why (etc) and finally the great-great-grandmother says "I never had a pot big enough."

Perhaps this is the case with optical sizing.

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