You have decided to go on bended knee and ask your beloved the most important question you will ever ask. You would like to record the event for prosperity without letting your soon-to-be finance know that something is up.
The first thing you should consider is the location where you should pop the question. Ideally, it should be outdoors with an easily concealable location where the photographer can position themselves or a place where people like to take pictures anyway. The place should also be a romantic one, say a park, or by a lake, or anyplace that is special for both of you. Such locations provide a great background for the proposal shots. Timing and even the weather are also very important. Lighting is always a consideration when taking candid photographs.
A little bit of pre-planning with the photographer is also very important. You will want to get the angles and backgrounds just right in order to get the perfect series of shots. Those include the one where you go on bended knee and present the ring, the one when your significant other reacts with surprise and, it is hoped, joy, and of course, the all-important first kiss of the new engagement after they say yes.
Everyone hires a photographer for the wedding. Everything is choreographed enough that it is relatively easy to record the great day. However, every wedding starts with another great day, when the proposal is made and accepted. If you manage to record that event, you can relive it for many years and bore the kids endlessly with a retelling of the story, properly illustrated, of course.
Naturally, you can try to save money by getting a friend or relative to record the proposal. However, the danger always exists of that person being spotted, ruining the surprise. A professional photographer who is experienced in this sort of thing is worth the extra outlay of cash.