Hey everyone, so I was wondering if you guys could answer a few of my questions. So how do you find the correct exposure for your flashes when you're out shooting? So I usually meter for the ambient and then at that point how do you set up your flashes? I personally just chimp until it looks about right but I feel there has to be an easier way. Also, I've looked a little bit into Guide Numbers but don't fully understand the process? Thanks for your time!
I set my exposure for the ambient and then use ETTL flash (the camera sets the flash output based on a reflected-light preflash),
or, I use a flash meter and set everything manually.
With the former I know pretty well from experience what level, if any, of Flash Exposure Compensation (FEC) to dial in for the look I'm after, but I can also use the histogram and the LCD review to tweak the flash output if it's not right at first.
Jay-Cub Photo wrote:
...I've looked a little bit into Guide Numbers but don't fully understand the process...
You're not alone. I had to learn it in school many decades ago, but my first decent flash had a calculator scale on it that would show what range to shoot at for a given f-stop and ASA level, or what f-stop and/or ASA to use for a given distance, so I never spent much time trying to calculate everything using the GN approach.
There's nothing wrong with the way you're doing it. As you gain experience, you'll be better able to anticipate what power level of your flash will be needed. Lots of really good photographers do it that way. You didn't mention it in your post, but a bit of thought about the ambient is also important, because it establishes the basis of your entire photo. Slightly underexposing the ambient, for example, enables you to make your flash-lit subject more dominant in the image. Overexposing with just a bit of fill on the shadow side is also a perfectly viable strategy. Either way, dialing in your flash "to taste" is often more easily done by chimping than by using a meter, unless you want to be really precise.
Since switching to digital cameras with clipping warnings that's what I use. It tells me when and where both the ambient and flash are causing a loss of highlight detail.
The thing to understand about flash outdoors it that it is needed because when the ambient is exposed for the highlights (per the blinkies) the sensor can't handle the contrast and will record the midtones and shadows darker than seems normal. An easy to grasp strategy to overcome that contrast problem is to put the sun DIRECTLY BEHIND the subject as rim light. That allows you to first set shutter and aperture to keep the sunlit highlights below clipping with detail then INDEPENDENTLY raise the shaded side to match what camera sensor can record to what you typically see.
In backlight first get the ambient lit highlights are 1/3 stop below clipping via the warning in the test shot playback. Then I add flash until things in the front like white clothing are 2/3 below clipping. That gives me detial in the sunlit white clothing with a slightly darker shade of white on the shaded side of same garment. The shot below was taken that way with one 580ex flash on a bracket:
I've got several tutorials on my site which explain and illustrate that: http://photo.nova.org
I normally use ETTL flash outdoors because it's simpler. That and high-speed sync is why I switched to Canon flash after years of using Vivitars manually. But if using Manual mode on the Canon flashes I'll use a "binary search" approach to find the correct power level for any given situation. I'll start at 1/2 power, shoot, evaluate. Then the next one will either be at Full power or 1/4 power. With 2-3 test shots I zero in on the level of power needed to match the ambient conditions at that distance.
"Balanced fill flash" on Nikon bodies is another viable option when there's not enough time to go through the aforementioned shoot-test-repeat processes. Balanced fill works in matrix metering mode (but not spot metering) in conditions where the background is brighter than the subject. A brief article on iTTl-BL can be found here.
If you are outside and want to balance the ambiant and use flash as fill the first thing to do is lock the camera on manual. If shooting in any auto mode, including ettl flash the camera is making adjustments for you. You will never see what is really happening. After that remember fast shutter will reduce the ambiant but allow in more flash. Slow shutter will allow the same amount of flash but allow in more ambiant. If you only want fill then expose only for ambiant then add flash until you see almost no difference, This should just add light to the eyes while keeping the natural light look.Add a bit more to taste depending on the look you like, clothing etc. If using ettl (camera in Manual) then dial down flash -1 or -2 until you see the lack of flash on the subject. In time you will be able to have it adjusted with 1-2 test shots because you know a starting point having done it enough times. My go to amount is 1/8-1/4 flash as a starting point but I am also looking for shallow DOF most of the time. I almost never use full power but then I try to avoid bight sun and having to match it. I shoot in shade or less bright evening conditions.
jefferies1 wrote:
...fast shutter will reduce the ambiant but allow in more flash. Slow shutter will allow the same amount of flash but allow in more ambiant.
@ BrianO
When using flash you are really making 2 exposures. The shutter speed controlls the 'ambient' light or background light and the flash controlls the subject light.
Increasing or decreasing shutter speed will darken or lighten the ambient light. The flash will illuminate the subject pretty much the same when changing the shutter speed.
Increasing the flash increases the light on the subject. More flash does not affect the ambient light (unless your inside and it bounces off walls/objects).
TMGraphics wrote:
...Increasing or decreasing shutter speed will darken or lighten the ambient light. The flash will illuminate the subject pretty much the same when changing the shutter speed.
Exactly! But jeffries1 said "fast shutter will reduce the ambiant but allow in more flash." That doesn't match my understanding, and is also not consistant with his second sentence where he wrote "Slow shutter will allow the same amount of flash but allow in more ambiant." The latter does match my understanding; changing shutter speed -- within the camera's sync range -- has no effect on the flash, only on the ambient.
So, I was seeking his explaination in case he knows something I don't.
