Balancing Flash Output To Ambient Light

I was assigned to make a photograph at the San Mateo County Bar Association's 100th Anniversary dinner. I had contacted the event coordinator and asked for a "Bride, Groom, Maid of Honor, Best Man" grouping, which is my way of saying I wanted only the most significant participants from the event.

Cave Photography: I often photograph in venues that aren't well lit, but this location was as dark a setting as I've ever seen. There was enough light to eat by, but not much more. I scouted a suitable location for my shot, and found a position that provided an interesting background in front of me, and a slightly warm bounce surface behind me. Next, I made four exposures to help me visualize the background. This is done without flash, since I wanted to establish a base-line exposure.

With an aperture of 5.6 and an ISO of 800, I made four exposures at the following settings:

• Upper left: 1/80
• Upper right:1/16
• Lower left: 1/8
• Lower right: 1/2

Making these four exposures helped me decide how much detail the background lights would add to the photo. The long exposure times are not a "free pass" when you combine speedlights into the exposure mix.

From my last exposure settings, I photographed my hand to see the amount of ambient light on my subjects faces.This photo showed that the ambient would add to any additional light from the speedlight. When I saw how warm the lighting was, I changed my White Balance setting to the Incandescent preset and made mounted my SB-80 with the CTO gel already installed. By taking a quick "selfie", I established a starting point for my image.

 

Here's the final image once again. You can see enough architectural details lit by the existing lights.But the long exposure time does have some side effects. You can see the blurred people moving in the background. What's worse is the bleeding of the ceiling lights into the edges of some of my subjects. Look at at the enlargement below, and you'll see what I mean.

Notice that the ambient light is adding to the shadows created by my speedlight key light, My incandescent compensation (gel on speedlight and Incandescent white balance preset) lighting should rendered more neutral skin tones, in spite of the walls being warm-toned (just enough to be considered off-white in color). I could have avoided this be simply decreasing my exposure time, but I would have lost a great deal of ceiling detail. I tried imagining the photo taken at 1/8 of a second, and was not to pleased at the prospect of a background that could pass for a "galaxy of stars".

In case you wondered, this is Marsha, my harshest critic. A San Mateo resident, she does peruse the San Mateo Daily Journal, and when the photo finally appears in print, I'm sure she'll see it, and through her thoughts and actions, let me know exactly how she feels about it lining the bottom of her cage. She pretty much has the same reaction to all of my work.

So be mindful of the contribution any existing light will have on your flash-lit photographs. There is a point where the color contamination may well ruin you photograph. Just be prepared to make some modifications on the fly, and be thankful for that little LCD panel on the back of your digital camera.

Telephoto Lenses - A User's Primer

As a young photographer, I was fascinated by telephoto lenses. Perhaps it was from watching too many wildlife shows on PBS. It would be many years before I'd appreciate long lenses for their perspective-flattening qualities more than their ability to photograph at much longer distances.

I was asked to comment on using telephoto lenses in the field.  There are several factors that must be understood it long lenses are to be used successfully.

Variable Apertures: It is less expensive to build a variable aperture zoom lens than one where the aperture remains constant throughout the zoom range. Shown here is my Nikkor 75-300 AF lens, easily obtained for $100 - $130 from eBay at the time this post was written (I paid considerably more when I purchased my specimen from a local dealer a few years ago, but it was still a bargain). Today, the lens is less popular that it was when it was introduced in 1989 because it's an AF (not an AF-S) lens, meaning you'll need to focus manually with the D3xxx and D5xxx series Nikon bodies. Second, its push/pull trombone zooming mechanism (supposedly) "inhales" dust into the lens' interior. And third, the front element rotates while focusing, annoying if you're trying to use a polarizing filter.

Notice the official designation (see photo, above), which means:

• If you use the lens at 75mm, the widest aperture available is F4.5.
• If you use the lens at 300mm, the widest aperture available is F5.6.

Notice that there are three focus indicators: This lens is not a true zoom, but a Variable Focal Length Lens, meaning that at different focal lengths, the plane of focus shifts. This isn't apparent when the lens is used normally, but in the rare instances when you need to know the camera's to subject distance,  you'll need to select the distance index appropriate to the focal length.

To prevent some unexpected aperture changes during zooming, think of the lens as a 75-300mm F 5.6 lens, and set the aperture accordingly.

Telephoto Lenses And Maximum Exposure Time: There was, and is, an old rule regarding the longest possible exposure time for any lens when hand-held. The rule is as follows, with as modification for the APS sized sensors found on most digital SLR cameras:

Longest Safe Shutter Speed = 1 / (focal length of lens * 1.5)

                    = 1/(300 * 1.5)

                      = 1/450 second

At longer exposure times, the effects of the photographer's shakes and tremors become visible. This does NOT take into account your subject's movement. You could properly freeze a Olympic speed walker or a snail race, but not an arrow in flight. This assumes that you're holding the lens properly, with your elbows tucked close to your body and the top of the camera resting against the bones beneath you eyebrows. Oh, the 1.5 is an adjustment because the APS sensor increases the usable focal length of the lens.

Joe McNally posted "Da Grip" a while back. Check it by clicking here.

Vibration Reduction (VR): Vibration Reduction (Nikon), or Image Stabilization (Canon) is an important feature, especially when using longl lenses. Call it magic, but it allows a steadier platform for the shooter working with with longer exposure times.The improvement provided by VR is often expressed in stops. For example, let's say we have a lens that when VR is engaged, it provides a 2-Stop improvement in performance. In the world of long lenses, it means that if your exposure dictates an shutter speed (exposure duration) of 1/125 of a second with VR off, you should achieve similarly sharp results if your exposure time was 1/30 of second, or four times as long. If you gain these two stops, you could shoot at an aperture two sizes smaller for more depth of field, or a lower ISO setting for improved quality.

This is not an absolute: In a discussion on lens choice,  David Ziser reminded us that VR or IS is not a guarantee of sharper images; It simply improves the probability that you image will show less degradation due to photographer tremors.And some reminders: VR must be turned on if it's going to work, it may not work properly when the camera is mounted on a tripod, and decreases battery life.

Now What? If there is a legitimate reason for not setting your aperture and shutter speed manually, I would suggest the following procedure:

• Set Your ISO: Chose an ISO to start. I would start at ISO 400.
• Set you camera for Aperture Priority Exposure Automation: This allows for exposure automation with an aperture that you select, and the ability to choose a high ISO value for the corresponding decreased exposure time.
• Select Your Preferred Aperture: If I were using this lens, I would set it to 1 F-Stop down from 5.6, or F 8.0. My reasoning is that lenses are seldom sharpest when used "wide open" (at maximum aperture), and by stopping the lens down one stop boosts the performance a bit.
• Make A Test Shot and Check The Exposure Time: After making a test exposure, check to see how the camera responded. If the shutter speed selected is 1/450 of a second or briefer, you're good to go. If not, go back to the first step and up the ISO another full stop, and repeat.

In The Field: When using automated exposure mode, you'll need to use the camera's Exposure Compensation feature to bring the exposure exactly where you want it. Remember that changing the aperture will have no noticeable effect on the overall appearance, as the shutter speed will adjust up or down, following your aperture choices.

One final suggestion:  If possible, get a shooting position where the sun lights the subjects from the front. Fighting for shadow detail with most telephoto lenses is a loosing battle due to physical limitations associated with long lenses.