"Op" doesn't usually translate as "for", except in some specific case (like "wachten op" = waiting for).
Those exceptions are the thing that makes prepositions so complicated. A lot of verbs come with their own prepositions, and these are not consistent between Dutch and English.
Did anyone else get Mitch Hedberg vibes?
"I was in downtown Boise Idaho and I saw a duck. I knew the duck was lost, because ducks aren't supposed to be downtown. There's nothing for 'em there. So I went to a Subway sandwich shop. I said, "Let me have a bun." She wouldn't sell me just the bun, she said it had to have something on it. She said it's against Subway regulations to sell just the bun. I guess the two halves aren't supposed to touch. So, I said, "All right, put some lettuce on it." "That'll be $1.75!" I said, "It's for a duck!" "Oh, then it's free." I did not know that. Ducks eat for free at Subway! Had I known that, I would have ordered a much larger sandwich. "Let me have the steak fajita sub, and don't bother ringing it up - it's for a duck! There are six ducks out there, and they all want Sun Chips!"