Strobe and Sunlight – How to?

I’ve had a couple people ask me about how to create the lighting effect in the following image.

It’s one of the various lighting techniques that I teach in my workshops (check this blog, or e-mail me for details). I find there are a number of roadblocks in learning photography that tend to stop people in their tracks until someone gets them over the hump.

One of those was the relationship between the shutter speed, aperture, and light. Until you really understood that relationship, you were forever doomed to shooting in automatic modes and thus severely limiting your creativity. But once  you finally understood it, it opens up a wealth of new opportunities for creativity and further learning while abandoning the ‘green box’ modes.

The relationship and control between strobe light and available light is another one of those stumbling blocks. And in some cases worse, because it also seems opposite of what you were taught with regard to light, shutter speed, and aperture. And in fact it is, so you need to unlearn some principles with regard to exposure, and learn a new one that just seems so obviously wrong!

On top of what you already know, when balancing strobe and available light together, add these to your memory;

If you want to change the exposure of the available lighting, use the shutter speed.

If you want to change the exposure of the strobe, use the strobes power setting.

If you want to change the exposure of the image overall, (both available light and strobe) use the aperture.

Some background first;

The reason why the above works is because the flash duration is shorter than the duration of the shutter speed. Typically, the strobes flash output is in the thousandths of a second. Lets say 1/1000 for the sake of argument. A typical camera shutter sync speed, the speed at which you need to stay below when shooting with flash, is no faster than 1/250th for most SLR cameras. So the shutter never has time to effectively regulate the strobes light output in any way as the flash has finished firing well before the shutter speed has expired.

I.e., the shutter opens, the flash fires  in the beginning of the exposure in maybe a 1/4 of the time the shutter is open. The shutter stays open much longer in order to properly expose of the available light in relation to the time the flash fires. Since all of the light from the strobe is delivered immediately upon the shutter opening (this is called first shutter sync), the effect of adjusting the shutter speed has no effect on the strobes lighting. It’s already contributed all its light to the image long before the shutter ever closes. So the shutter speed does nothing to adjust the exposure of anything that is predominately illuminated by the strobe. Thus, you can use the shutter speed and aperture independently to balance the two light sources together. With that out of the way, the following will be better understood. So on to how the above image was produced.

First, I shoot manual mode almost all the time, except when shooting fast action in changing lighting conditions. I find it faster to shoot manual than trying to second guess what the camera and strobes are thinking on my behalf. Rather than try to understand what they are thinking, equate that to what I want, then figure out what controls I need to twiddle to readjust their ‘thinking’ to match my desires, I just tell it what I want and it does it. I eliminate the middle man (camera and flash CPU and software) and do a direct Star Trek Vulcan mind-meld to the camera (brain to hands to manual controls). Fast, simple, easy.

So, the camera was set to manual mode. I knew I would be shooting directly into the sun, so a small aperture would be needed. I also know I need to stay below the flash sync speed of 1/250th for the camera and strobe to operate properly. Using the sunny 16 rule as a start, I file away in my head 1/125th at f16 as a good starting point. That would give me a real close exposure appropriate for normal daylight conditions.

But we have some ripples here. It wasn’t direct sun, but was overcast and hazy in the background. So I knew I would lose about a stop or two to the overcast. I’m guessing maybe 1/125th at f11 now. I also want a slight bit of under exposure to add a more dramatic feel, so I’m going to under expose the image, and I generally like about 1 to 2 stops under.

I want to adjust the shutter speed first as it will allow me to adjust the expose for the background without affecting the flash power I would need. If I just closed the aperture down, it would require more power from the flash to compensate the smaller aperture. When balancing strobe to daylight, the strobes power is the last thing you want to squander away. So I generally adjust the shutter speed first till I hit the max sync speed, then start to adjust the aperture further to get where I want to be.

I mentally adjust the shutter speed from 1/125th to 1/200th, but know I will still need more since that’s well under the stop or two I feel I need to underexpose the background. I also adjust my aperture as well to f22, which puts me at 1/200th at f22. I dial that into the camera and take a test exposure.

I love the sun and sky, but the background is too dark. But I am within 1 stop of where I wanted to be. I ask my assistant to move in to the frame so I can also start to dial in the strobe exposure. I open up the aperture to f16, dial up the strobe to around 1/2 power, and take another test exposure.

The background is still a bit dark for what I wanted, and the strobe power level isn’t enough. I could adjust the shutter speed down one stop to bring up the background, and then adjust the strobe power up one stop to bring up the light on the subject. That would waste some of the strobes power, and there is a much better way.

Since I want the background lighter by one stop, and the strobe brighter by one stop on the subject, in this case I can use the aperture to adjust them both (see the above rules). And I am not wasting that extra stop of strobe power I would have lost if I just added more power. I kill two birds with one stone. I open up the aperture from f16, to f11 and get the following.

A closer look at the LCD and histogram and decide that f11 is just too bright for what I am after. The sky is more washed out, and I feel the lighting is also to bright on the subject. I adjust the aperture to f14, which will darken both at the same time.

Much better. But I really wanted the sky a bit darker, but also don’t want to darken the ground behind the subject and in the distance which would result from further adjustments to the available light exposure. So instead decide I will darken the sky a bit in post. The available light exposure is good as is. At this point, I move the model into place. Mike put a nice X on the ground to mark the spot just for Anya. Once she is in place, I erase the X with the physical clone healing tool (my sneaker ), so I won’t have to deal with it in post. I ask her to just relax for a moment while I take another few test exposures to see how the light is falling on her.

Other than a cloud that rolled in to ruin my nice sun star effect in the previous images, we are pretty much ready to go. I do a couple more test exposures, check the histograms, zoom in to check focus, added some warmth to the scene (adjusted kelvin), etc. By then the cloud has moved away, I get into a lower shooting position, call for the model to ‘do her thing’,  and we start shooting. The result is the first image in this post.

Here are a few others shots in different locations during the session. All use similar techniques to setup the lighting, but are varied in the effects they produce based on the mixture of the two light sources. I’ll try to find time to add a couple new posts with more details on the images below. Look for the one with the natural rainbow that appeared after the thunderstorm that passed by!

The following images are outtakes from the shoot and have not yet been edited, only exported from Lightroom. But I wanted to give you a feel for the variations that can be made by adjusting the available light and strobe light in different ways.

The above image used a White Lightning 1600Ws strobe on camera left for the main lighting on the subject. My assistant Mike, was also ducked in the weeds on the right and behind with a 580EX set to give just that hint of accent lighting on Anya’s left arm. Its a subtle effect, but brings a lot of production value and interest to the image. All three light sources were balanced appropriately.

The above image goes for a darker effect, as well as just being underexposed, and would be perfect with storm clouds in the background. But the overcast didn’t have any interest in the clouds, other than being dark and forboding. I used a WL 1600ws strobe on camera right for a subtle fill, while the Canon 580EX created the nice accent lighting on their right sides (image left). It adds nice definition to their cheek bones and separation from the background. I feel the strobe on camera right should have been a tad brighter, which I did adjust for some of the images.

This image shows a more balanced effect between all three sources. The available lighting is a bit underexposed, but not by much compared to the others above. The 580EX on camera left, and the white lightning 1600ws on the right, were pretty even in their light output. This does answer the question whether or not a small 580EX is enough to handle balancing with daylight. Although, it was overcast at the time needing about 3 stops less power. My assistant did comment that he liked shooting with the 580 at such a low power setting because of the short recycling time, so it does has ‘longer legs’ to deal with direct sun.

This is another image with the same lighting setup as the image preceding it. The 580EX on the left is set slightly higher than the 1600WS on the right.

A quick look at the setup used for many of the images here. It doesn’t show the 580EX which was had held by my assistant. Note the rainbow in the background! Just luck really. It was a great addition to the thunder and lightning show we were treated to as the storm moved past us.

Here is one of the images that resulted from the above lighting setup (minus the rainbow which appeared shortly after). The only difference is the addition of the 580X that my assistant is hand holding which is absent in the above lighting setup. It provided fill light from the right side of the image.