Which one to keep?

[nealjpage]

Long story short, I have two 50mm Pentax K mount lenses and I'm going to sell one. How should I decide which to keep and which to sell? They're both f2.8. Serial numbers, if that helps, are 8159551 and 3613037. Even though the number is larger, I'd say the first one is older. Is there any real difference, or should I just chose one out of a hat?

 

[hobbes28]

Do you have a quarter?

Actually, I'd keep the one you're more fond of. If you don't prefer one, pull out that quarter.