Let’s first discuss equipment. A digital SLR camera is a must since you can easily adjust your settings and change the lens. Always bring a couple of zoom lenses either a 15mm–55mm or a 70mm–200mm lens. If one isn’t working, you can switch it out for the other one.
Also, bring a tripod. You may not need it, but it’s better to be safe than sorry. Props are a must. If a classic engagement photograph is not working out, try throwing in a prop that means something to the couple. It can change the whole feel of the photograph.

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Always bring extra memory cards. You want to take as many photographs as possible, especially if you’re going for getting a natural, candid photograph. And, bring an extra battery in case the one that you are using goes dead. It also makes for a great way to catch a candid shot if you pretend like you’re changing out your batter.
Bring a flash just in case. Since the flash goes along with the discussion for lighting, it’s something to mention now. For indoor photographs, you may need the flash. But, there’s a caveat with using a flash. You want the photographs to be as natural possible so you should refrain from using it as much as possible. A flash will over-exposure your subjects and will dull the ring.
Here’s a hint about photographing the ring. If you use a flash, it could reflect off of the ring. But, to make the ring brighter in natural light, polish it. Give it its own natural shine so that it really stands out in the photographs.