I have four typical lighting scenarios:
1. Mixing ambient and flash: flash as fill. The primary light source is the existing light. I'm only using flash to supplement the existing light, usually to add a little fill to the shadows.
2. Mixing ambient and flash: flash as key. There is still some ambient light, but it's not bright enough to serve as the key light, therefore I am using flash as the key light.
3. Maximizing flash. In this situation, I'm in bright outdoor conditions and I'm using flash either to supplement the existing light or to replace it with flash. In either case, I'm concerned about maximizing the output from my flash.
4. Controlled setup.
FLASH AS FILL
When I'm using flash as fill, I don't use U1 or U2. These are my settings:
- Max sync speed: 1/320 Auto FP.
- Auto ISO: on. Minimum shutter speed: 1/125 (D7000) or auto - fastest (D600, D7100), i.e. 2 stops faster than the 1/focal length rule. I like using a high shutter speed to increase the probability of sharp shots.
- Minimum flash shutter speed: 1/125.
- Exposure compensation for flash: background only.
FLASH AS KEY
I set this as my U2 mode for quick access. Note: I use U2 more often than U1 because it's next to the PASM modes. At around sunset, the amount of ambient light usually dips and if I have been shooting with the settings that I use for flash as fill, the shutter speed usually becomes too slow. So slow that it typically results in flash blur. To remedy this, what I usually do is underexpose the ambient, so that the primary light source becomes the flash, and the effective shutter speed is the flash duration.
Here are the settings I use:
- Sync speed: 1/250 (D600: 1/200). I turn off HSS because I need all the flash power I can get.
- Exposure mode: aperture priority.
- Auto ISO: on. Minimum shutter speed: 1/15 (D7000) or auto - slower (D600, D7100). Because ambient is sufficiently underexposed, the flash will freeze the subject. It's ok for the shutter speed to be slow. However, I don't want it to be so slow that the background will get smeared due to camera shake. 1/15 is as slow as I can hold it while still making the background look clear enough.
- Exposure compensation: -1.3 EV. I want ambient to be underexposed to avoid flash blur.
- Minimum shutter speed for flash: 1/15.
- Flash exposure compensation: 0 EV for D600 and D7100 (both of them: exposure compensation for flash: background only). For D7000: +1.3 FEC to offset the reduction in flash exposure from the -1.3 exposure compensation.
By the time I get a breather, ambient light levels have usually dropped so that most of the light is coming from artificial light sources, which means that they will be stable and therefore I switch to manual exposure.
I have this set as my U1 mode. If I see that my flash is underexposed using my normal settings despite being on full power, I want to be able to quickly change my settings to maximize my flash output.
Here are the settings I use when I want to maximize flash:
- Sync speed: 1/250 (D600: 1/200).
- Exposure mode: Shutter priority.
- Shutter speed: 1/250 (D600: 1/200). To maximize my flash output, I set the shutter speed to the sync speed.
- Auto ISO: on. Minimum shutter speed: 1/15 (D7000) or auto - fastest (D600, D7100), i.e. 2 stops faster than the 1/focal length rule. In all likelihood, this won't even come into play because I already have my shutter speed set to sync speed.
- Minimum shutter speed for flash: 1/15.
For controlled setups, I don't use U1 or U2. I use whatever settings are required for the situation. If I'm building the light with flash (what David Hobby calls a bottom-up approach), then I minimize ambient first. I switch to sync speed, the base ISO, and a sufficiently narrow aperture to delete the ambient. Then I add flash as needed, starting out with fill, then key, then other lights (rim light, hair light, background light, etc.).
If I'm using ambient as the primary light source (top-down approach), then I start out with an exposure for the ambient light and adjust as necessary.