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Studio lighting on camera flash

As I was preparing for this, taking pictures of a sample pinewood car, I was able to get a good exposure simply using the umbrella and softbox. However, I wanted to try to further soften the shadows using my canon 430ex flash. I kept the studio lights configured and set as they were earlier for the 'successful' shot. I started by pointing the flash directly at the car, but was getting harsh shadows. I then attempted to bounce (again, the intensity of the studio lights were set exactly as before), but this time, the image was very much underexposed.

Since I didn't change the intensity of the studio lights, and bounced the camera flash, my assumption was that the brightness would be the same as my first successful shot and I would simply fill in the shadows. Removing the flash from the camera gave me the 'better' exposure again. Any thoughts on why the combination of the studio lights and flash underexposed the shot?

Thanks!
Bryan

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January 07, 2008

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January 07, 2008

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January 07, 2008

You could use the on-camera strobe as a fill.

Maybe this will help but be warned I am boring and uninteresting.

First let’s talk about the studio lighting. Most shots look better if we can spawn an illusion that the scene is illumined by just a single light source. This is true because man has existed for countless centuries under a single light, the sun. When we induce artificial lighting and it seems to come from multiple locations, the results can look weird (exceptions abound). This is especially true in photography whereby our media is a two dimensional reproduction of a three dimensional subject. To bring about an illusion of depth we need well place shadows at the correct strength. A skilled photographer knows how to play the shadows.

Now the camera is limited as to the range of light (dark to bright) it can handle. Likely the shadows will be rendered too dark because photography has yet to catch up with the human eye/brain (dynamic range). So we need to toss some light into the shadows as this reduces the difference between highlight and shadow. We call this range of difference the lighting ratio. Generally we want a 3:1 ratio as this is a good match to film and chip. The result is shadows, not too dark, we can see detail in the shadows.

How to achieve: We generally try and simulate midday sunlight by placing a lamp high to simulate sunlight 10AM ~ 3PM. This lamp is called the main. Best to place it with all others tuned off. This helps you see the shadows it makes. For starters place it high and off to the side about 45° off center.

Now place the second lamp called the fill at lens height near the camera. To preserve the one light illusion the light from this fill must be adjusted to deliver less light energy than the main. This is best accomplished with a light meter. We would like the fill subordinate by 1 stop or 50% or ½ power (all say the same thing. Again, placement is near the camera because we are filling from the cameras viewpoint.

We can use distance lamp-to-subject to make the brightness adjustments (other methods work too). Measure fill-to-subject distance and multiply by 0.7 (decimal seven). This calculates a closer main-to-subject distance. If the main and fill are equal in brilliance these revised subject-to-lamp distances establish the fill energy at the subject plane, reduced 50% as compared to the main. This is 3:1.

Why 3:1? Consider that the main delivers 100 units and the fill delivers 50 units. Now the shadows are out of the line of sight of the main thus they only receive only 50units of light and that comes from the fill lamp. The highlight areas receive light from both the main and the fill. Thus they get 150 units. So the ratio is 150:50 which reduces to 3:1.

If the fill is further reduced in half it delivers 25 units. The highlights get 125 and the shadows get 25 the ratio is 125:25 = 5:1 a nice more theatrical lighting.

Alan Marcus (marginal technical gobbledygook)
Anaheim, CA ammarcus@earthlink.net

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January 07, 2008

Here’s some exposure information from one of my classes.
In teaching this class I keep trying to find ways to say that you have moved into the land BEYOND metering. When you use a strobe meter you get a response that tells you how to make a middle density, but it doesn’t tell you how to make it look right. There is no automatic way to make it look right, only the application of brains can do that. When I make a shot with strobes and a digital camera, the first thing I do is to put the camera on manual and I will pay no attention to the meter in the camera. The only things I pay attention to are the proof image on the camera back and the histogram. More than metering these two things tell you about your image. Let me suggest a plan for seeking the right exposure: 1) set the shutter speed to the sync speed, 2) set the aperture to your middle aperture, whatever that is on the lens you are using, 3) take a picture, it will be wrong, 4) move the aperture dial to let in more or less light based on test exposure 1, you can look at the histogram to help determine how much to change the aperture, but the proof image should tell you if you need to change a lot or a little, 5) more test exposures and changes of light placement and light power until the strobes are right, 6) change shutter speed to balance values between existing light and strobe light, this will require more test pictures. This same technique will work if you are mixing strobes and daylight. This was why the Polaroid bill was so high with film cameras, but with digital these test exposures are free, so we should not be afraid to make them.

This is the essential trick with strobes, to evaluate and change our images in search of the right levels for our lights and our exposures. With the histogram and the proof image on camera or in the computer we have better tools for creating the right exposure than any meter could give us, but it does take repeated testing.
Thanks, John Siskin

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January 07, 2008

First, I was shooting in manual mode and, much to what John mentioned, it was trial and error when I was just using the strobes. In fact, I did start with the sync speed of 1/250 (so it's good to know I was on the right path John!) and adjusted the aperture. Aside from the trial and error, I changed nothing on the camera.

Second, it was only when I started using the 430EX flash when the 'problem' started occurring. Take the flash off, and the exposures with the strobes worked good (for me, anyways). I was syncing first with the sync cable, but then discovered (albeit a surprise) that I could trigger the strobes with the camera flash - another thing I'll be playing with soon.

I'm afraid if I set the flash power on the 430EX to 50%, the exposure would go even darker, with no improvement on lessening the shadows.

I uploaded 3 examples of what I ran into. They are labeled accordingly.

Again - thanks for the great response and information. Hopefully, you'll see from the photos what my challenge is.

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January 07, 2008

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January 09, 2008