Flash Versus Ambient: By The Numbers

Original You Tube video can be seen here.

Warning: Potentially Disturbing Images. I look pretty awful in these photos. Some days I look worse. Can't explain my Conan O'Brian hair.

I made this series of photos for my Outdoor Flash class to illustrate the role existing (ambient) light plays in the foreground - background relationship so far as exposure is concerned. There are three important points to be made:

• The exposure setting for your background may not be the same as that of your foreground. 
• The background and foreground settings may not be mutually exclusive.
• Your camera's internal meter can only meter what it sees, which may be different from what you want.

Photo #1 Exposure: 1/8, F 5.6, ISO 200

I am standing in front of a closed exit door in our main meeting room (Photo #1). I am being lit only by the overhead fluorescent lights. The camera is mounted on a tripod with a subject-camera distance of about 8 feet. Setting the camera's exposure mode to Aperture Priority, I made this photo at F 5.6, my usual starting point. Exposure compensation was set to zero.

For the record the shots were made with an APS sensor Nikon D80 with a zoom lens set to 135mm. This was to insure that the background in all subsequent photos would completely fill the frame. This will be important in determining a suitable background exposure.

Photo #2 Exposure: 1/20, F 5.6, ISO 200

 For this shot (Photo #2), I opened the door to reveal the solar panels in the parking area adjacent to the building. Again shooting in Aperture Priority, I got this image. The Matrix Metering system attempted to reconcile the extreme differences between the background and the foreground, resulting in an exposure where neither background nor foreground were rendered properly, the two extremes being "averaged" mathematically. Clearly, this is not a satisfactory photograph by anyone's standards, but unfortunately, similar to so many I see when indoor subjects are photographed against an  outdoor background.

Photo #3 Exposure: 1/250, F 5.6, ISO 200

To get a handle on a more suitable background exposure, I simply stepped aside and let the camera evaluate the background minus the foreground (me). Without changing the aperture, the camera selected an exposure duration of 1/250 of a second, which is a full 3 1/3 F-Stop difference (Photo #3).

Now we have a slight problem. The preferred exposure time for the background at F 5.6 is 1/250th of a second. Since the D80 can't synchronize a flash at this speed, we need to find some equivalent exposure (aperture/exposure time) combination where the flash will work (maximum exposure 1/200th of a second).

Two factors to consider:

• Can your speedlight deliver enough light at your chosen aperture?
• Will the corresponding exposure time introduce noticeable camera shake?

Ideally, I would, in the Manual Exposure Mode, choose a combination from a series of equivalent exposure settings, one that would allow for proper flash synchronization. Any of the following might do:

1/200 @ F 6.3
1/160 @ F 7.1
1/125 @ F 8.0
1/100 @ F 9.0

Photo #4 Exposure: 1/200, F 8.0, ISO 200

As you can see from the caption in Photo #4, my choice of exposure settings underexposed the background by 2/3 of a stop. Notice that the blue sky is bit more saturated (true blue) in Photo #4 than it is in Photo #3, a happy outcome.

Reminder:Your camera needs to be in the Manual Mode, using the aperture and exposure settings you like best. If you leave your camera in Aperture Priority or Shutter Priority, you may wind up with an overexposed background like the one in Photo #2.

Photo #5 Exposure: 1/200, F 8.0, ISO 200, plus speedlight on camera

Adding Flash: For Photo #5, I attached an SB-900 (it was handy) to the camera's hot shoe and made a shot. The background remains exactly the same as it was in Photo #4, but now the foreground is illuminated by the speedlight. Not great lighting by any means, but a simple photo made by exposing the background with a manually selected F-Stop and shutter speed, and then allowing the iTTL speedlight to simply do its thing. As I warned, another in a series of very disturbing photographs.

Photo #6 Exposure: 1/200, F 8.0, ISO 200, plus speedlight off camera

Getting The Flash Off-Camera: By using a light stand and an extension cable, I was able to raise my light source to a height of about 8 feet off the ground, but since I'm 5' 6" tall, this translates to only  2' 6" above the center of my face.

Both Photos #5 and #6 were made with direct flash, which is to say that no modifiers were used. I only wanted to illustrate the interplay between the background and your foreground subject. So long as they the foreground illumination is not affected by the ambient or background illumination, you are free to adjust them both to achieve the effect you want.

Non-TTL Adjustment: Vivitar 285 HV

 The Vivitar 285HV - Non-TTL Automation: The main reason that these older speedlights are relatively inexpensive is the "outdated technology" the use to automate exposure. When automatic flashes first appeared in the mid sixties, they offered the photographer the promise of properly exposed images within a range of distances. Instead of explaining how they worked, let's look at h how you might use the automation on a Vivitar 283-285 unit.

Composite #1: Color Coded Settings on the Sensor

Adjustment of the flash's output is controlled by a dial on the sensor. There are four color-coded settings (Composite #1):

• Yellow: This setting will allow you to use the largest aperture within the sensor's range.
• Red: This setting allows you to use an aperture two full F-stops smaller than the Yellow setting.
• Blue: This setting allows you to use an aperture two full F-stops smaller than the  Red setting.
• Purple: This setting allows you to use an aperture about one F-stop smaller than the Blue setting.

The 285/285 HV sensor dial has four manual settings: Full, one-half, one-quarter, and one-sixteenth.The Vivitar 283 sensor adjustments are very similar, but lacks the half, quarter, and sixteenth output settings.

Photo #1

This is the Calculator Dial of the 285HV (Photo #1). If you take a close look you'll see a white triangle which serves as an index mark for the ASA / ISO setting. The Calculator is currently set to ISO 200 (one click to the right of ISO 160).

If you look closely, you can see the four color-coded wedges matching the color patterns of the Sensor Dial. You can see the following suggested apertures:

• Yellow: F 2.8
• Red: F 5.6
• Blue: F 11
• Purple: F 16

With your camera set to ISO 200 and your Sensor set to Red, the dial suggests setting your lens aperture to F 5.6. So long as the sensor is looking directly at your primary subject, the flash will meter out enough light to properly expose you subject, based on the amount of light that is reflected back.

The final step to set the lens aperture based on the sensor's color code. A little complicated, but this type of non-TTL metering will work on any camera's hotshoe.

Photo #2

The ISO can be changed by rotating the Sensor Dial to 400, the circular scale advances to indicate values that are one F-Stop value smaller that those for ISO 200, just as you might expect (Photo #2). Again, a simple design that is reliable, but subject to the variables of sensor alignment.

I must give credit to the engineers who designed the basic Vivitar flash platform. A number of features border on genius. For example, the sensor eye can be removed and one end of the extension cable inserted into the flash body. The camera end of the cable is mounted in the camera's hot shoe, and the sensor inserted. You can see in Photo #3 that the cable, attached to the hot shoe, keeps everything properly aligned.

Photo #3: Extension Cable Installed

Photo #4

To add to the versatility of the extension cable, there is a small contact at the base (camera end) that allows one to install a Wein Peanut Slave (Photo #4), if the situation forces you to regulate the flash output manually.

This might not seem like a big deal, it means that you can completely enclose a 285 HV within a softbox. You can control, and trigger the flash from outside the softbox with a Peanut Slave

One last feature is the 4AA cell battery holder. You can keep extras pre-loaded with fresh batteries available for a quick battery change Also, if there's a battery leak, the insert, rather than the actual flash contacts, takes the corrosive "hit".

Pretty nifty, Little Vivitar 285!