The technique of determining ascenders & descenders has been discussed recently in font critiques. I think it deserves it's own discussion.@Hrant H. Papazian
mentioned his technique here
Here's how I determine my ascender/descender levels.
I work from the heaviest weight and design my f
. I decide if I want to keep the f
crossbar aligned with the x-height. I need to decide where it's more important to keep the ascender low or to keep the top of the f
from looking crushed. Then I use the f
to determine the height of the lowercase L
. The ascender height doesn't have to align perfectly with the f
, it just has to flow nicely. You can come up with all the theories you want but that fat f
has plans of its own.
Next, I work out the g
. The relationship between these letters is crucial so I design them simultaneously. I go back and forth, making adjustments. When I'm testing, I'm seeing how it looks in words with ascenders. Making sure it feels balanced. Or unbalanced if that's what I'm going for. Then I based the other descenders on what looks best with the g
. I'm not too concerned about using up valuable descender space because the descenders usually aren't the lowest glyphs. The comma accent and lower circumflex almost always lower than the ascender unless I'm deliberately crushing them. In the lightest weight, there's less pressure on the top of the f
and the x-height is usually different. I re-evaluate the ascender and descenders try to maintain the balance established in the heavy weights.
I'd like to hear how other people determine their ascender/descenders.
It might be useful to fork this discussion into extenders for display types and extenders for text types.
Other than that: on an ad hoc basis, whatever looks right for the face in question.
I do try and consider the Extra Bold (i.e. boldest weight) before the face is too set in stone, so that it can fit the same bounding box as the rest of the weights.
I don’t know that I would go so far as to codify the formula for myself as you have, but I will now be more likely to consider earlier on how my xht+descender relates to capHt.
Call me old-fashioned, but my initial core letters for designing are H h i l n o p and I just work out my key vertical proportions intuitively at that point, keeping in mind considerations like accents and room for heavier weights.
More and more frequently now, I find myself sketching at least a circumflex and cedilla to factor the accent space more intentionally earlier in the design process.