More On-Camera Fill Part 1

Photo #1: 1/500, F 11.0, ISO 200, Aperture Priority, Exposure Compensation -1 stop

Party School: The Adult School has a large non-native speaking population. As such, learning English can sometimes include lesson in American culture, as it was on this Friday before Valentine's Day. The school was heading into a three-day President's Day weekend, and the general feel was just a bit festive. 

Since I really wasn't out to "win a Pulitzer", I decided to just shoot some fun shots that would test the ability of N-TTL speedlights to effectively lighten the shadows. The camera was a Nikon D70 with a 2.8 24mm Nikkor prime and my SB-30 mounted in the hotshoe. Because the SB-30 hadn't been neutered, I would be forced to limit my shutter speed to 1/500 of a second or slower. Despite this, I set my the body to Aperture Priority, which would allow me some freedom if I moved out of the direct sunlight and into the shade. But for all intents and purposes, I was shooting in the manual mode, since the shots never went below 1/500 when I shot in the sunlight. The speedlight was not set to F11, but rather to F 5.6 to minimize any overexposure caused by the fill light overlapping the areas illuminated by direct sunlight. Photo #1 is typical of the photos made with this setup.

Photo #2: 1/500, F 11.0, ISO 200, Aperture Priority, Exposure Compensation -1 stop

Photo #2 is an interesting variation on adding detail to the shadows. My subject’s lower torso is actually in the shade of the building behind me. The supplementary flash added detail to both his  face and his jacket so nicely that you might not have noticed it. 

Photo #3: 1/800, F10, ISO 200, Aperture Priority, Exposure Compensation -1 stop

Changing It Up: The 1/500 of a second top synchronization speed was starting to bother me, so I changed to a Nikon SB-26 I had just "neutralized" so I could sync at all speeds. I also attached an SD-8 6-AA supplementary battery pack. While the increase in weight and bulk were obvious, this new combination gave me three advantages over the on-camera SB-30. The new combination positioned the flash tube higher above the lens axis for marginally better lighting, increased my available power, and decreased flash recycle time. Photo #3 shows the advantage of switching to a neutered flash. The record shutter setting was 1/800 of a second with no blown highlights, the byproduct of the minus 1 stop exposure compensation.

Photo #4: 1/500, F 10.0, ISO 200, Aperture Priority, Exposure Compensation -1 stop

Foreshortening And Wide Angle Lenses: Assuming that you can work comfortably at such close shooting distances, you're bound to experience two consequences: foreshortening and light fall-off. Foreshortening is when objects closer to the camera appear disproportionally large, and somewhat brighter. In Photo #4, you can see that the left hand appears much larger than the right one. Also, the skin of one's open palm is more reflective than the back of the hand, resulting in a combination that makes the hand appear much larger than it is. Burning the hand in post production can reduce the visual impact.

Photo #5: 1/250, F10, ISO 200, Aperture Priority, Exposure Compensation -1 stop

Paper Plate: Working in a free-style manner, I was free to experiment a bit. I remember that in the past, resourceful photographers would use a white paper plate as a reflector to improve the quality of the lighting. This worked well with an older flash whose head could be tipped skyward. All you had to do was just hold the plate at a 45 degree angle to the head, a relatively simple task. This raised the light ever higher over the lens axis, giving the best lighting yet.

Photo #6: 1/200, F 10.0, ISO 200, Aperture Priority, Exposure Compensation -1 stop

As you can see from the "glare" that outlines these two dancers (Photo #6), the sunlight is obviously coming from behind. The longer exposure in these last two photos (remember we're in Aperture Priority) allowed more detail in the classrooms in the background, making the two photos much more believable. The "ghosts" problem wasn't adequately addressed by the factory lens hood. However, when using a film formatted (FX) lens on a APS-sized sensor equipped camera, there are going to be some gaps in the protection provided by the hood. I once modified a Hasselblad adjustable bellows lens hood to work on a Sigma 24mm F 1.8 lens, and may be forced to return to that solution because it actually worked.

On-camera speedlight fill is a useful techniques when photographing outdoors. It is almost a requirement for event photographers who must provide photographs that are both salable to the subjects and reproducible in the society pages of the local newspapers. I'll talk more about light modifiers for on-camera flash in a future posting. In the mean time, here's one on the Gary Fong Light Sphere.

When "Speedlight Present" Is Absent

So far I've neutered a total of four Nikon Speedlights (one SB-24, two SB-26s,  and one SB-28). As a precaution, I've blue-taped, or installed blue velcro, on each of these units, primarily as a reminder that the Speedlight Present pin has been disabled. This is not an issue with the D70s they were modified to be used with, but this modification could cause some problems if any of these modified speedlights wander into a camera bag with my D300 or my D7000, two heavy-use cameras that can't perform the sync-at-all-speeds magic.

The Speedlight Present feature is a safety device that prevents a camera from firing at any shutter setting that exceeds the manufacturer's top synchronization speed. When functioning normally, Speedlight Present prevents the user from accidentally selecting a speed faster than 1/500 of a second for the D70; 1/250 for the C90, D300 and D7000; or 1/200 for the D80. These speeds are not arbitrary; they are the minimum speed where the entire sensor is exposed to the light coming through the lens for a single instant.

The shutter mechanism used in the digital single lens reflex has its roots in the original Leica camera, which dates back to 1925. It consisted of two rubberized cloth curtains that marched past the film using a mechanical clockwork mechanism. Early versions moved from right to left, probably as a concession to the positioning of the gears and springs required to make the system work. At some point, the shutters were redesigned to accommodate a metal curtain that moved from top to bottom, something like a roll-top desk. Here's how the two-curtain shutter works when the camera is set to the maximum flash synchronization speed. When the shutter release is pressed:

• The first curtain falls, exposing the top of the sensor first, until the entire sensor is exposed.
• At this exact moment, the flash is fired, allowing all of the photosites (photo-optical sensor that yields one pixel of data) of the sensor to be lit simultaneously. 

• The second curtain falls, first covering the top of the sensor, until the sensor is completely covered.

When shutter speeds briefer than this maximum synchronization speed are chosen, it is impossible for all of the pixels to be lit at once. At these speeds, a slit (gap) separating the two curtains travels across the sensor. All of the photosites get their serving of light, but not all at once.  The slit could be made to vary in width, depending on how much light is required to properly illuminate the image. A wider slit translates into more time for each pixel to absorb the light necessary for proper exposure. A narrower slit, less.

I made a series of photos to illustrate the slit, and what could happen if I deploy the wrong speedlight. Because optical lens systems actually invert the image, I modified the samples as a nod to technical accuracy. If you inadvertently put a neutered speedlight on a camera incapable of high speed synchronization, like a Nikon D90, you'll get results similar to these:

1/200 of a second                                            1/250 of a second                                          1/320 of a second

At 1/200 of a second, the first curtain has advanced and disappeared into the lower reaches of the cameras innards. The second curtain waits briefly before advancing, giving each pixel its full 1/200 of second. The entire surface isn't illuminated all at once: the  pixels at the top edge are lit before those at the bottom.

At 1/250 of a second, the top synchronization speed for the Nikon D90 I used for these photos. The second curtain will advance the moment the first has disappeared past the lower edge.

At 1/320, you can see a darkened area at the top edge of the frame. The second curtain started its advance before the first curtain fully disappeared, creating a gap between the two that was not as wide as the frame. Since the flash fired the moment the first curtain had completely disappeared, we catch the leading edge of the second curtain as it advances into the image area.

1/400 of a second                                      1/500 of a second                                               1/640 of a second

In these last three images, you can see that the second curtain is in motion a bit sooner for each decrease in exposure time. Remember that that the flash is set to fire when first curtain is completely hidden by the lower edge of the frame, and that the rear curtain follows, leaving the proper gap for each exposure setting.

I've been really pleased with the modified speedlights, as it gives me the option to carry one as my third, backup unit. I can now stuff a D70 in my camera bag (or carry a spare on my neck) and know that I can use the magic all-speed-synchronization if I need it, and not have to worry about finding a neutered SD-17 flash extension cable to keep with the flash,or the extra hand needed to use it.

Non-TTL Flash Automation

Photo #1

When all is said and done, my favorite "legacy" Nikon speedlight is the SB-26 (Photo #1) because it has a built-in SU-4 optical slave, fully adjustable manual exposure in 1/3 stop increments, and Non-TTL exposure automation in one-stop aperture increments. For the purposes of this posting we shall define Non-TTL (N-TTL) exposure automation as the ability to deliver proper flash exposure within a given range by varying the duration of the flash pulse through a sensor built into the flash itself.

Because there is no direct communication between the camera and the speedlight, the ISO and aperture settings of the speedlight must be set to match those of the camera. In use, one should definitely NOT chose the camera's shutter priority exposure setting because N-TTL relies on a constant F-Stop in order to work. 

Photo #2

If you look at the cropped image at the right (Photo #2), you can see where the sensor is located. It's mounted on the flash body so that it always faced forward, even when the flash head is rotated or tilted. Because the circuitry is completely contained within the unit, N-TTL flash can fully function with any camera when triggered by a PC cable or a standard hotshoe, depending on the flash. The SB-26, like the legacy flashes introduced after the SB-24, has a supplementary PC connector on the side, should the PC cable be your only triggering option.

Here’s how it works. Assume that both the speedlight and the camera are set to ISO 200 and an aperture of F 5.6, and that the two are attached. Let's make a theoretical test to see how N-TTL exposure automation works.

• Imagine that the flash/camera combination is placed five feet from a blank white wall. Take a photo. Based on a ISO and aperture settings, the flash will provide enough light to properly expose the wall with a burst of light, which in our hypothetically example might last 1/2000^th of a second. 

• Next, imagine moving the flash to a distance of ten feet from the wall. The inverse square law tells us that when we double the distance, we must increase the amount of light by a factor of four. When a photo is taken, the N-TTL sensor will measure the light bouncing back from the wall and increase the flash duration to 1/500 of a second, quadrupling the light output.

• The opposite is also true. If the distance is reduced to 2.5 feet, the flash duration would be cut to one-quarter, or 1/8,000 of a second.

One important footnote in the N-TTL story is the inclusion of Thyristor Circuitry. In early units, any  excess flash power that wasn't needed to expose the film was "dumped" in a quench tube and lost forever. The power was essentially wasted, meaning that every shot, no matter how close, was at full discharge. The introduction of the thyristor allowed any excess power to be re-cycled within the unit, allowing for a much faster recycle time and longer battery life.

N-TTL Automation In Action: I tested the consistency of N-TTL exposure by mounting a 60mm 2.8 Macro Nikkor on a D600 body, ISO set to 200, aperture set to F 7.1*, shutter speed 1/160 of a second. I mounted an SB-26 in the hotshoe, set it to F 5.6 at ISO 200, and set the camera to manual focus since I would be photographing a blank white wall and there wouldn't be anything to focus on. Four exposures were made at distances of three, six, nine, and twelve feet. The camera and flash settings were not changed between shots. The composite (Photo #3) was made from the histogram displays from the respective images with three feet at the extreme left, and twelve at the extreme right.

3 feet                                                 6 feet                                         9 feet                                             12 feet

You can see from the "white" histogram (the one at the top), that the exposure is very consistent from shot to shot. Each time the flash moves farther from the wall, the sensor allows more light to escape. When enough light for a proper exposure has been dispensed, the excess power is shunted away from the flash tub and returned for use during the next flash.

This series of photos demonstrates (to my satisfaction, at least), the N-TTL flash automation is capable of providing consistent exposures over a variety of distances. This neither proves nor disproves the accuracy of the exposure, only that given a constant set of exposure conditions, the discharge accurately dispenses the correct amount of light over the four tested distances. By adjusting the size of the lens aperture, the results can be fine tuned to taste. But at least we know that Non Through The Lens exposure automation is capable of accurately compensating for changes in flash to subject distances.

*Several old timers recommended selecting a lens aperture 2/3 of a stop smaller than the one suggested by the flash. This would, in theory, underexpose your flash images. I'm willing to take this on faith.

Nikon SB-30 Micro* Speedlight

http://www.kenrockwell.com/nikon/sb30.htm

While checking e-Bay for Nikon speedlights, for found a Nikon SB-30 for $30.00. Too great a coincidence to not purchase it. And since it was sold by a brick an mortar store in the midwest, how could I go wrong?

Ken Rockwell, a reliable and "to the point" photo blogger, started a writeup on this flash unit, but the last time I checked, it was still under construction. He did make some wonderful photos of the unit, which I'm including here, along with links to his article. Granted, I can see why this flash wouldn't be Priority One on his, or anyone's, blogging to-do list, but having purchased one and played with it a fair amount, I can think of a number of uses for it. Incidentally, for a posting from DPreview, click here.

The unit uses a single CR-123 battery, which contributes to its small size and rapid recycle time. However, the batteries are expensive when compared to AA cells. It does not offer iTTL metering as does the Nikon SB-400, my other tiny flash. But it offers far more exposure control features than you might expect. For starters:

http://www.kenrockwell.com/nikon/sb30.htm

TTL Exposure Metering: If you're a digital photographer and have a D1x, or D100, or even a Fuji S1 or S2, you're in luck. These cameras can utilize the speedlight's basic TTL metering. I suspect that if you're reading this post you don't have any of these DSLR cameras, but if you do/did, you've got TTL exposure automation with your flash.

Non TTL Flash Exposure Metering: The unit has its own sensor that meters out four measured bursts of light that will provide proper exposure for four basic aperture settings at ISO 100 and four more at ISO 400. Need something in between? You can easily extrapolate what you need for ISO 200, and maybe even ISO 800. While a full post on non-TTL flash automation is justified, it suffices to say that for fill purposes, the SB-30's non-TTL metering mode should work well, or well enough.

+/- 1/2 Stop Exposure Compensation: This is an interesting tweak, but rather limited.

3 Manual Output Levels: You can set the flash to manually discharge a "full" discharge, plus 1/8 and 1/32 power discharges. This could be very handy in situations where a precise (and small) burst of light is all that's needed.

Built-In IR Panel: Like the Nikon SB-50 DX, there is an infra-red panel you can use to cover the flash tube for use as a wireless optical trigger. Unlike the SB-50, there is some white lite leakage, a definite distraction when photographing anything with functional eyes.

SU-4 Style Optical Slave Modes: The orange M and A allow for firing the unit as a optical slave, but only at full power in the M(anual) mode. Haven't quite figured out the A(uto) mode, but just having the slave feature is cool enough.

So where does this unit fit in? First off, it's small size (it could probably fit in a cigarette box) makes it a great fill light for a compact camera that can take advantage of the speedlight's manual controls. Used in either the non-TTL or the manual mode, you can arrange for a fast fill light solution, or a more precise flick of fill light, depending on what you need. It sits very close to the lens axis, but not close enough to cast a shadow when your wide angle sports a petal lens hood.

I'm pretty impressed with the flash, and plan to use it for filling some upcoming outdoor events. We'll find out whether I picked a winner or a loser!

*Micro is my descriptor. When compared to the SB-910, it is REALLY small! 

February 10 Addendum: I used the flash with the IR Panel in place to trigger a wall-bounced SB-800 in SU-4 Mode. Using a 60mm 2.4 Macro on a Fuji X-E1, I made this selfie (Photo #1):

Photo #1

Incidentally, the shot is full width, with the cropping affecting only the top and bottom edges.

Photo #2

As a subject, I didn't find the white light leak particularly annoying. In fact, I really don't remember seeing it. But in this cropped photo (Photo #2), you can  see the distinct two-spot "signature" made by the SB-30, but you have to look very carefully to find it. While this would be an easy post processing fix, it could give you some grief if the reflections show up on eyeglasses. Just the same, this feature proved very convenient!