A quick follow-up from the last post on hard light. This time it's a brief look at lighting ratios which I mentioned in passing. In my book the difference between highlight and shadow brightness is about 10 times more important than overall exposure. Obviously that's within reason but for the most part a bit off - even a stop or more is not that big of a deal. You can adjust overall exposure in post and it will look about the same as if you shot it that way in the first place. As you know I am a big fan of getting it "right" in camera but a third of a stop either way in overall exposure is not going to make a significant difference in the way your photos look assuming you "correct" that after the fact.
Here's the caveat - as long as you have the ratio between highlight and shadow in the scene that you actually want. No matter whether you find the light, bring the light to the scene yourself, modify it, whatever - this is a big big deal. In fact in my mind a lot of the hoopla of techno crap distractions is to somehow circumvent actually figuring this out, looking at it, and making decisions about it when you are making pictures.
That may be a bit of a stretch but in a way it's very true. HDR, auto-magic fill flash bullshit, the magic of highlight/shadow controls in post-processing, etc, etc, etc. All this is about forking around with the ratio between your highlights and your shadows. Here's a secret - no how no way is any of it worth a damn if you don't figure this out in camera. Well for landscape guys I guess some sort of exposure stacking/HDR crap is a good short cut for neutral-grads or crazy shaped neutral-grads but for the most part I am talking about single exposures of people. Really studying lighting ratio and conditioning yourself to see it the way cameras see it is a critical part of this whole photography thing.
I talk about it a lot in the Lighting Field Guides - not in a pedantic rule based way. More of a getting a feel of it way. I mentioned last time that I tend to find the look of hard light as a main light attractive at lower lighting ratios. Sometimes this happens in nature with the sun under extremely rare circumstances in various environments and conditions. More often than not it doesn't - hence auto-fill-flash. Too bad that two hard sources from distinctly different directions and color temperatures looks kinda fake and speed lights are hard pressed to do much against direct sun if you make them big and soft like natural fill is. You need about 17 of them. Enough of that.
Let's go with another take of Anastasia. At the top you see an example of a somewhat lower ratio between the main light and the fill pretty much the same as last time. Just a different shot. Ambient conditions serving as the fill - speedlight as the main light. Somewhere near a 2:1 ratio. Meaning that there is only about a stop difference between where the flash is hitting the subject and where it's not. I did mention briefly that it doesn't mean that the flash is literally a stop brighter in terms of output. that's because at closer ratios (typically the ones you want) exposure is additive. Where both the fill and the main sources hit the scene/subject it's adds up. Hence if you measured it independently the "output" is probably about equal. Kinda hard to do with ambient being so high - can't really turn that off. What you can measure is the difference if you care to.
That's not super important compared to getting a feel for what it looks like and realizing that one measly stop in difference is pretty huge. What happens when you lower the ambient just one tiny little stop more and keep the places the speedlight is hitting about the same. In these conditions that's just dialing up the shutter speed one notch from 1/60s in as used in the shot at the top - to 1/125 second. That knocks the ambient down and doesn't effect the flash exposure - well you would think it doesn't and it doesn't in terms of how much light the flash is contributing. In practice you will need to dial up the flash a hair due to the fact that the combined ambient/flash is now a bit lower.
Here's the result of that one stop lower ambient fill - techno speak for a 4:1 lighting ratio. The fill is now two stops lower than the main light. More accurately the places where the flash is hitting as two stops brighter than where it is not.
Holy smokes batman, that's different. Yep - only one stop less fill. Everything the same. Cut and pasted settings. Actually a heavily modified version of VSCO 400H. White balance - contrast - color - everything - same lens (50mm on the D600). Slightly different framing and obviously different pose otherwise the same. These were specifically 2 frames apart in the camera.
One stop of fill different - night and day. There is a universe of options between those two lighting ratios of 4:1 through 2:1. Of course I shoot at even lower or closer ratios as well as higher/wider but in between that tiny little 1 stop of difference is a really good bet. The techno gobbl-dy gook is not real important. Having some measurement helps some people as sort of a backstop to ensuring they are under the same general circumstances - other's not so much. For everybody it's really important to get a feel for it more so than the terminology or the measurements.
Consider this yet another sweet spot.