Morning shirow, welcome to these forums.
I think your boyfriend is a lucky chap that you want to do that and I'm sure he would love the thought of you buying him a lens. I have a thought that I want to share and I hope you understand where I'm coming from. I'll explain, buying someone else a lens imho should be done with caution as everyone's camera kit is a personal thing. I'm not saying for one moment if you was to buy him a lens he would be ungrateful but there is a risk it might not be the one he would really want. A few things to ponder about. Does it have to be a surprise? Has he given any clues to what he would like? Has he tested/tried any and given hints to one he would like. I say this as for example I might prefer a Cannon xyz lens but you might get him a Sigma abc lens. Then he might be in the position of having a lens but not his first choice but might not want to say and hurt your feelings and could get awkward, I don't know tbh as I don't know you two. Normally when someone posts recommend a lens they are given a few suggestions but when it comes to buying it, it's personal choice/taste, how it feels, does it perform how they want, too heavy, focous fast enough etc etc. Very tricky thing.
It could be a case of buy him a lens but with a view he can exchange it. Take him with you. Ask him out right what he would prefer.
My wife last year bought me a tripod & head and she thought as it was best part of £200 she thought it best to get the one I would want rather than guess. I admit it did kill the surprise but everytime I use it I think "what a great tripod, my loverly wife bought that for me X ".
I hope that made sense and I didn't come accross negative and rain on your parade. What you want to do is a loverly thing but can be very tricky to get the right one. It's bloody hard enough choosing kit for yourself let alone for someone else.
Good luck with your purchase, your heart is in the right place and I'm sure he will love what ever you do.
Agro
