A nice label is useless if the cap falls off

On set, lenses get thrown into cases and pulled out in a hurry. Being able to see which one is which without opening every pouch is a small thing. Small things add up fast on a long day.

So a cap with the lens name or focal length on the front makes sense. But the first version shouldn't start with the font. It should start with the fit. "Custom" doesn't mean much if the cap drops off in the bag, or if you need two hands and a swear word to get it off.

Measure where the cap actually grips

A slip-on cap sits over the outside of the lens front. The filter size printed on the lens can describe something completely different. So measure the rim where the cap will sit, in more than one direction. Look for a hood bayonet, a taper or anything raised that could catch.

If you always leave a filter on that lens, test with the filter on.

And keep the glass in mind. The cap should hold onto the rim, not touch the front element. A test print is the fastest way to find out whether your measurement and your printer agree.

The useful bit goes first

On a cap I want to recognise the lens first and admire the design second. A short name, the focal length, maybe an owner mark. That's enough.

The lens-cap generator also lets you add the aperture and a logo. You don't have to fill every field just because it's there. Check the preview at the cap's real size. Tiny, beautifully rendered type on a monitor turns into a grey smudge in a dark camera bag.

If you're doing a whole set, use the same naming pattern on every cap. Consistent beats six separate design experiments. The kit can still have personality. It just needs to stay readable at a glance.

Print it in a way you can repeat

The download includes a two-colour 3MF, aligned STLs, an A4 sticker PDF and a plain blank cap. If your printer does two colours well, great. If not, the separate files or the blank cap plus sticker are the saner option. To be clear, it's a digital package for your own printer or a print service. No cap arrives in the mail.

Print one before you print the set. Let it cool, put it on and pull it off a few times, and feel the inside for rough edges. It should stay put while you carry the lens and come off without a fight.

Then write down the dimension that worked. "It was something around 80" is not a production system. I say that as someone who has trusted his own memory more often than it deserved.