Why spend $20 on a good-quality, purpose-made macro lens for your iPhone when you could spend $10 on 3-D printing your own holder and another $4 for a glass lens to put inside it? That, my friends, is a saving of six whole dollars. Six American dollars that Appsman — the maker of this clever lens — is doubtless frittering away on a night of frenzied celebration. And if you, too, want to make yourself six bucks richer, then read on.