Aperture, Shutter Speed, Manual and Program (or P for Poor-fessional)
Camera Modes at Events
You noticed that Auto is not on the list. If someone had just now asked me whether my cameras have the green setting, Auto, I might have to look because I haven't thought about it in years. I am used to just feeling my way by tactile method on the knob, going second nature between Av, M and Tv. I don't even remember the direction to turn for P any more (kidding).
Wedding scenes can change every hour or faster. You can be in a church one minute and on the beach ten minutes later. You can go from needing multiple flashes to a single hi-speed flash. You can go from Manual exposures indoors to Aperture priority outdoors, to Shutter priority for controlling your maximum flash synch.
Auto actually does have a place, and that's when you go to a personal family get-together, don't mind shooting jpegs, and want your images to look like higher quality versions of point and shoot cameras.
Balancing natural light with flash at events
Many wedding photographers today are not very comfortable balancing flash with natural light. Admirably, they do not want their images looking flat-lit from an overpowering on-camera flash unit. But many have decided that they will be just natural light photographers. In part, this has been promoted by high profile speakers whose videos show them shooting wedding without any flash unit in sight, and certainly not on the camera hot shoe. Unfortunately, these instructors in some cases don't explain that natural light was a choice for that scene and not necessarily a universal solution to all of their event coverage.
Natural light can be beautiful, or it can be muddy. Using it when it falls nicely on the subjects' features may result in soft, directional light that sculpts the faces and the scene. Sometimes you can escort your subjects to a better light location. But the majority of scenes might not give you such an easy job. Significantly, unless you position your subjects correctly, natural light might not give them any catchlights in the eyes. They can end up with a flat, scary look. If the light is from the ceiling they might also have shadows in the eye sockets. When shooting only natural light you may also end up with color temperatures not properly adjusted by Auto White Balance. Correcting color in Lightroom does not remove the shadows from the eye sockets nor does it eliminate the noise in the images from needlessly using high ISOs. And catchlights? Forget it. "Perfect natural light" actually comes from a direction that gives your subjects dimension, a hair light, and catch lights. That's a tough combination to achieve unless you also use a reflector held by an assistant. Okay, now things are improving, but in reality who has time for this during a busy wedding? Certainly not your bride and groom.
The practical solution, if you have good natural light and no assistant and no reflector, is to add just a hint of on-camera flash - just enough so that it looks natural and leaves other curious as to whether you used any flash at all. With practice and experience, your photos can look outstanding and professional, while the amateur's images will have too much on-camera flash or an underexposed, muddy look.
Main, or key on camera flash should be avoided when possible. With event flash units, a very natural look can be accomplished by having an assistant managing a main light on a pole (or raised by hand if you get a tall assistant) while your camera flash serves as a fill light. The fill should be anywhere from 2/3rd to 2 stops under the correct main light exposure. You will have to experiment, but a nice, dimensional image will result. The technique is great for table shots and activities inside a banquet room. If you do have enough natural light to work with, the same technique will work. The natural light can be your main light and the camera flash can be your fill, providing catchlights to your subjects and removing any shadows in the eye sockets. This is really quite old school, but effective.
Balancing color temperature can be another challenge. Outdoors you can combine sunlight and fill flash as they work within similar color temperatures. Indoors you have to be more careful. A church might have strong overhead tungsten lights over or behind the altar. You have three options. Option one is to use natural light as fill and flash for main lighting, color balanced for the flash. It is most important that your subjects be properly and evenly lit. The warm light on the scene looks nice in some cases, but be careful that your subjects' hair do not take on an unnatural golden glow. Option two is to overpower the scene with flash (single or multiple, and reducing shutter speed), and let the background go dark. Option three is to put tungsten light modifiers on you flash units, set the camera to tungsten, and then both the background/overhead lights and the flashes will have matching color temperatures. Option four is to reduce the church lights to insignificant levels, place remote flashes behind the subjects to light the church background, and use one or multiple flashes for frontal key and fill lighting.
However you choose to light the subjects at that particular location, check your LCD carefully for even lighting at the beginning of the session and then you can light the rest of the formals evenly, saving you time in post-production. Make good notes for the future for when you return to that place. In my part of the world it is important to know what to do quickly as typically the churches only give you 15 to 20 minutes for posed photography.
It's always about the light. You have to either find it or create it.