I agree on the aperture, keep it 5.6 or above. Maybe even 6.3 or 8 depending on how close you are. The closer you are to the subject, the higher the number needs to be.I see!
Your best option might be to use a 70-200 or a 135 prime and get further back from them while also keeping them far in front of the background so it will blur. The distance would also help diffuse the fill light from the camera. Unfortunately, the 430 might struggle with distance over 8-10 feet, esp if you used a diffuser. If you are far enough away from them, the diffuser would not be necessary.
Get a friend and go practice at that venue at the same time of day. Test different ideas, lenses, flash setups, etc. Let us know what you decide and how it goes!! Relax and have fun!
Do you really think fill flash is necessary? I would think you would want to shoot at F2.8 for the best blurred out background, but I guess not. I will experiment with 2.8-8 when I shoot this friday. I also have a 70-300 Tamron which already has those apertures you guys suggest...
You won't be able to shoot at f/2.8 because your long lens can't do it
. Edit: Whoops! Sorry! I mixed up which lens you have. (And a long lens that could would likely be the 70-200 f/2.8, which is worth more than all your equipment combined.) And assuming you rented a faster long lens, there will be too much light in the daytime to be able to use f/2.8 unless you used a ND filter. Even at ISO 100 you will likely not have a fast enough shutter to allow f/2.8. And even if you did, one of your subjects would be out of focus. Trust me, you probably don't want to go below f/5.6. You can blur the background with distance behind the subject at f/5.6 but you can't get multiple faces and prom dresses in sharp focus at f/2.8
.Yes, fill flash will be necessary
. Otherwise you will have undesirable shadows in the faces, esp if you have backlight or a bright background. Discussing lighting techniques for this is a whole other discussion and it doesn't sound like you have the equipment anyway. In this case, with your limited equipment, ETTL is your friend and it will be easier to tweak/adjust the highlights later in LR with possibly a little too much light vs too little/more shadows in the faces.There are several levels of challenge on shoots like this
. Focus, DOF, background, lighting, posing and people management. Practicing with someone (or several someones) ahead of time would be of great benefit. Rehearse the entire thing at the same time of day so the light will be the same
. Set up your equipment, pose your subjects, focus, camera settings, people herding, talking to the subjects and finally examine the images in LR and see what needs to be tweaked and what needs to be adjusted in camera.I would seriously recommend that you get LR 5 to correct and improve the images
. You will no doubt have shadow, white balance, shadow, contrast challenges that you will want to improve (and learn from) after the fact.Most of what I'm saying here is basic stuff
. There are many other CR members here with way more portrait experience than I have that could probably offer more experienced advice and suggestions
.But in this case, I think you need to follow the KISS principle and not add any more equipment or techniques than you can handle
.Everyone here at CR are glad to help and know the stress and concern a photographer faces. The best way to achieve success is NOT spending a lot of money, it's PRACTICE!!!