Below is an image made with available light inside a chapel that has both flourescent and tungsten lighting. It's decent, but it's hard to find WB in such a setting with multiple types of light lol. I believe I went more with tungsten WB in camera and then played with it a bit more in post.
Decent image, but not a wow image right? Still, a good starting point and a solid image to deliver to a client :)
But look at what happens when you add flash in this situation. It almost puts a spotlight on them. I definitely prefer this to the first image.
So how was it done? Same formula as for outside. For the record, I don't use gels. Maybe one day, but I like the warmth that the tungsten gives off when I set my camera to Flash White Balance.
1) Expose for the background.
If you want it to be darker, speed up the shutter speed, just remember to account for your flash sync speed. I was at f/4, with a shutter of 1/250, ISO 2000.
For the whole ceremony, I was at ISO 2000 b/c I wanted my shutter speed to be high enough to avoid camera shake using the available light. So I just kept the same settings here for ease. I could have also lowered the ISO for these portraits, which would consequently slow down the shutter speed and have gotten the same result. I would just have needed more flash power, which is not a problem with my trusty Quantum T5D-R or whatever it's called.
Higher ISO = Faster Shutter speed (since camera becomes more sensitive to light) = Less Flash Power Needed.
Lower ISO = Slower Shutter Speed (camera less sensitive to the light, so gotta keep shutter open longer) = MORE Flash Power needed in that same situation.
Aperture is kind of arbitrary.. at least to me (omgosh, don't take my word as truth okay?). It's at f/4 in this case b/c.. that's the aperture that accompanied my 1/250 shutter to get my background to be the way I wanted it to be... I usually start at 1/250 and then adjust my aperture accordingly. But honestly, it depends on the situation you are in.. how bright or dim the ambient light is... it's just something you get with time. Sometimes I'm at 1/60th at like ISO 800. It just really depends. And I'm STILL figuring it out LOL.
Am I confusing? If so, I apologize in advance, AND I suggest you no longer read my 'How To's" LOL.
2) Light your subject!
Assuming you darken the environment a bit for more dramatics, your subjects will also be dark. So.. now that it's time to add flash, I do it manually since I'm using off camera flash. I don't care for TTL at this juncture, I just eyeball it.. and feel it's the easiest way to learn anyway. I start at around 1/8 power on my flash and.. if it's too bright.. I'll lower it.. if it's too dark still, I'll raise it. Simple as that!