Establish Outdoor Guide Numbers

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I now own several Strobist inspired manual-only flashes (Yongnou 560, the Lumopro 180 Quadsync, and the new Adorama Flashpoint Li-On) which I use more frequently now that my Fuji mirrorless cameras have become my "go to" cameras in the field. I keep a Fuji EF-42 flash when I need the convenience of TTL exposure automation, and can accept the unbearably slow recycle time. The Yongnou 560, when used with an accessory (Canon compatible) battery pack, gives me a fast recycle time and has pretty much become my indoor flash flash of choice.

Like most modern manual flashes, the light output can be adjusted down from full power in full stop, or third stop increments. Coupled with the modern digital cameras' access to extremely high ISO sensitivity levels, manual flashes are seldom used at full-power. This said, matching the output to the subject to flash distance will require some quick mental calculations. These usually involve Guide Numbers, a simple mathematical trick concerning the aperture and the distance for given ISO value. To put it another way:

Guide Number = Aperture * Distance

Backstory:Back in my film days, I did most of my best work with a twin lens reflex Mamayaflex which had a leaf shutter to control exposure. It suffices to say that leaf shutters couldn't be used for exposures of less than 1/500 of a second, but could synchronize an electronic flash at any exposure setting. In those days I was a Vivitar 180 flash, which had a guide number of 56 when used at half-power, a necessary setting if I was to shoot more than 40 shots for the rechargeable, built-in nickel-cadmium batteries. I committed to memory three critical distances; 5', 7', and 10', and three corresponding apertures; F 11, F 8.0, and F 5.6, as the appropriate pairings for each distance. Since I used Plus-X film with a nominal ASA/ISO rating of 100, the appropriate exposure time, based on the Sunny 16 Rule, would have been 1/100 of a second, 1/200 of a second, and 1/400 of a second.

I made an informal test while vacationing in Oroville, using a D70 and a single SB-800 flash to make a series of selfies from which a subjective guide number was determined. In a later post I calculated the light loss associated with Nikon's High Speed Synchronization using a Photovision White Balance Target. I liked the results so much that I decided to repeat the guide number experiment using the test target, a speedlight, a tripod, and a suitable indoor location (Photo #1, below)

A Simple Test: 

• I shot the test shots in our "Great Room", which has a very high ceiling and a maroon carpet covering the floor. For all intents and purposes, in non-reflective environment.
• I positioned a 24" Digital Calibration Target from PhotoVision exactly 10 feet from the speedlight I was testing.
• I mounted a 135mm F 2.0 Nikkor lens on D70 body, and set it to manual, ISO 200.
• Each of the three tested flashes would take their turns mounted in the light stand next to the camera. They would be triggered with a Nikon SC-17 cable.
• With each flash starting at full power output, I would shoot, check the histogram, and adjust the aperture until the histogram's midpoint was positioned exactly at the half-way marker.
• Since the flash to subject distance had already been determined, I calculated the Guide Number by multiplying the final aperture by 10.
• Once the guide number had been determined at full power, the flash output was cut in half, and the process repeated.

Photo #1

Here you can see the three histogram "peaks" representing the black point, mid point, and white point (Photo #2). A centered midpoint can be interpreted as a correct exposure for a typical subject with an 18% reflectivity, just what you might expect if an incident light meter reading had been made.

Photo #2

The calculated guide numbers were as follows:

All Flashes set to 35mm Beam Angle, 10’ from Calibration Target, ISO 200
Manual Power Setting	Yongnuo 560	LumoPro 180 Quad Sync	Adorama Flashpoint Li-On (manual)
Full Power	110	130	130
½ power	80	100	90
¼ power	56	71	63
1/8 power	40	50	45
1/16 power	28	35	32
1/32 power	20	28	22

Once I had compiled all of the is data, a thought occurred to me: If I selected a specific aperture, I could the select the output as dictated by the subject-to-flash distance.

Nikon Coolpix A, 1/500 of a second, F 11.0 ISO 200

Fast Forward to 2016. Due to the output limitations of the Fuji EF-42 Flash, I've resigned myself to shifting my flash output manually. In doing so, I've re-acquainted myself with the fundamentals of guide numbers. All of the tested speedlights can be set at full stop increments from full to 1/128 power. And two of them, the FlashPoint and the LomoPro, support 1/3 stop increments.

My photographic aesthetic has changed, too. Now, my background often includes large amounts of sky. In an effort to maintain a rich cyan color, I've started basing my exposure based on which aperture/shutter combination that gives me the best looking sky and letting my flash provide the illumination for the foreground.In this sample photo, you can see that I have both a blue sky and a hint of clouds at the given exposure settings. The foreground (the walls of my stairwell) is now dependent on supplementary lighting.  This same exposure setting could have been applied to a Nikon D70 which, like the Coolpix, can sync a flash at 1/500 of a second.

I chose the Yongnuo because the tested guide numbers aligned with existing apertures. F11 was chosen because this coincides with the aperture of choice when working with an ISO of 200 and a maximum synchronization speed of 1/500 of a second. It will also accept an accessory battery pack that will give faster recycle time.

Reverse Engineering: From the data gathered from my Yongnuo exposure experiments, I took each calculated guide number (Middle Column) and divided it by 11, my preferred aperture.The appropriate distance for the aperture could be seen at the right.

Yongnuo 560 (F11, ISO 200)
Power Setting	Guide Number	Optimal Distance
Full Power	110	10.0 feet
½ power	80	7.3 feet
¼ power	56	5.1 feet
1/8 power	40	3.6 feet
1/16 power	28	2.5 feet
1/32 power	20	1.8 feet

What Does It All Mean? Based on the table calculations, I would pre-set my camera to an aperture of F11, a shutter speed (exposure duration) of 1/500 of a second, and an ISO setting of 200.  I can then position myself so my flash-to-subject distance is 2.5 feet. Based on the table, I should select an output of 1/16 power and achieve a "proper" exposure. If wanted the flash to serve as a  fill, I could increase the distance by stepping backward, or if the flash is hand held, merely increasing the distance.

I'll be photographing an outdoor Lunar New Year celebration, so we'll see how well this system works.

Year Of The Monkey: Foster City, 2016

Photo #`

Another Chinese New Year in Foster City. Same location, and same exposure challenges. The window in the background faces the Foster City lagoon, and on a sunny day, creates a background that is almost impossible to expose properly. I was using forward and back bounce flash without the  benefit of a Black Foamie Thing. I was forced to use my hand instead. The photo was published on Page 1 of the February 17 issue.

Photo #1 was my favorite of the two photos I submitted. The young lady is playing a traditional Chinese Hammer Dulcimer. Behind her are the San Mateo/Foster City School Superintendent, two members of the SM/FC Board of Trustees, and the Mayor of Redwood City.

Photo #2

This second choice shot (Photo #2) is a bit crowded. The 28mm equivalent lens of the X-100 wasn't  wide enough lens to include more spectators on the left and all of the Lion's  rump on the right. I liked the contrast of the young lady's hand on the dark background, and while it appears she is trying to hypnotize the Lion, she's actually holding a cell phone camera.

Photo #3

The One That Got Away. This is the photo that I didn't submit because I forgot to ask the name of the teacher in the blue t-shirt. It has everything I could have asked for. The off-center composition is full of enthusiastic spectators, bringing the photo something none of my others had - the audience's involvement in the Lion Dance. The combination of window light from the left with my bounced flash fill gave the image more depth than the other two. Alas...

Photo #4

I rejected this photo (Photo #4) because the lion's black mane seemed to melt into the background, It didn't think it would reproduce well if accepted for publication.

Photo #5 - 1/500, F 5.6, ISO 800

Technical Notes: I used a Fuji X100S fitted with my newly acquired Fuji WCL-X100 adapter, believing that its 28mm equivalent view would be wide enough for use in these relatively tight quarters. I made all of these images with a Fuji X100S with the wide angle adapter except for Photo #1, which was made with an X-T1 with a 35mm 1.4 lens.

Lighting: I used forward and side directed bounce flash to boost the interior lighting levels. I used the Adorama Flashpoint Li-On speedlight in the manual mode, full output. The recessed skylight directly above the performers made it difficult to back-bounce, but when the speedlight was aimed camera left and bounced off of a wall, I was rewarded with soft lighting with a sense of direction, as you can see in Photo #5. One other point: You can actually see people beyond the back window.

Photo #6

This low-angle shot (Photo #6) was easily made by composing with the LCD instead of the eye-level finder. The composition has too much foreground for my taste, and was removed from consideration as soon as I saw it.

Photo #7

The finale for these young dancers was this circular formation. Forward bounce was used. I rejected it because it looked too much like last year's submission. And what's going on with the man in the window?

Photo #8

Here's a young man in a colorful costume (Photo #8). I wonder about the black and white jester's costumes, which look too Western to me.

Photo #9

Cute Kids (Photo #9).

Photo #10

Another Cute Kid (Photo #10).

Photo #11

This last flying leap (Photo #11) could have been used because I had the wherewithal to ask this young man his name. But there wasn't enough context to support the shot.

The X-100S with the wide angle adapter did well on this assignment. I particularly liked the leaf shutter's ability of sync at speeds faster than the 1/180th of a second in the T-1 body. Still, the mirrorless cameras seem to be missing something that the Single Lens Reflexes have, which is the sense that you are look through the lens and not at a computer-generate simulation. I'm not sure that I'll ever really get used to it, but I'll keep trying.

Science of Mixology at the Exploritorium

Photo #1

After 44 years inside the Palace of Fine Arts in San Francisco's Marina district, the Exploratorium moved to Pier 15 on the Embarcadero in San Francisco in April of 2013. I was an occasional visitor to the old location, and never had cause to visit its new digs. Times change, as do the requirement of transit and parking.

I contacted the Media Coordinator, and explained that I had been assigned to make a photograph. I included this line: “Since we are a local newspaper on the San Francisco peninsula, we are looking for (subjects) who live in our service area.” The event was offered to me as a “plum”, as I would be getting two VIP passes and all the delicious goodies that go with it. But I saw it as a chance to take a visit to the new facility off my “long” bucket list.

Photo #2

I spent a lot of time worrying about how I would make a photograph in so large a venue. With the Exploratorium’s architecture inspired by a minimalist “warehouse” school of design, I was faced with a huge open structure with no walls and a high, dark ceiling. Preliminary attempts to bounce flash proved futile, so I ran some test shots first using straight available light (Photo #2) and then with palm-bounced fill (Photo #3, below). While some images were produced, light still failed to reach the distance background, and my subjects simply melted into the darkness. I brought some extra speedlights for possible use as “highlights”, but without an assistant or two, there would be no way to effectively deploy them.

Photo #3

Photo #4

I finally found a large exhibit that was one of the Exploritorium’s permanent displays. I tried to imagine a photo that included the display and the exhibitors in front of it, but the juxtaposition of camera, foreground subjects and the background made impossible to light them all evenly (Photo #4). Again stumped, I abandoned the idea of direct flash. But I noticed I was standing in front of another permanent exhibit that did have a suitable bounce surface. If I were to move my subjects closer to me, my on-camera bounce flash could properly illuminate them. With my foreground lighting now established, I could now deal with the background.

Photo #5

The bounced flash would light my foreground subjects with soft, even lighting, but little light reached the background. To compensate, I increased my exposure time until there was just enough detail to reveal guests milling about in the background (Photo #5). I noticed that there was a ceiling mounted spotlight that could provide enough light to separate my subjects from the background if they were properly positioned in its beam. And if I could include that spotlight in the photo, the dark ceiling would be revealed for what it was, rather than just an underexposed dark region. To my surprise, the solution to the background problem emerged, and I was glad of it. Just then, these two young women walked by. Seeing I had a camera in hand, they automatically assumed I could use their cell phone to make a photo, and so asked. I countered by saying that if they would pose for me, I would instead send them a photo taken with my camera. They agreed, and the resulting test shot showed that my lighting solution would work (Photo #6).

Photo #6

While this was going on, the Media Coordinator and I kept in touch via cell phone. She had her people try to locate any Board members who might show, but none but the Board President himself was in attendance. By 10:00 PM, three hours after I had arrived, I called and told her that it was now or never, and asked that the she bring the Board President to where I wanted to make the photo. It was agreed that I would include her in the shot, since she was the only other Exploritorium staff member at hand.

When they arrived, I noticed that neither one had brought a prop I could use to help carry the shot. I asked them to wait while I tried to find the hors d'oeuvre hostess I saw a few minutes before, which of course I couldn’t. Returning, I asked if either of my subjects would object to holding a drink. When neither one minded, I quickly walked up to a small group of guests, introduced myself as a photographer, and begged them to loan me two drinks to use as props for my photo. In exchange, I’d take a group photo and send it to any member who would e-mail me. They agreed, and I now had two yummy looking drinks for my subjects to hold (Photo #1). In two minutes, I had seven variations on the shot. This done, my newfound friends retrieved their drinks and the group photo was made (Photo #7).

Photo #7

Photo #8

I immediately packed up my gear, completely satisfied with the final product. If you look closely at the image I submitted, you can make out the smiling face of my new best friend, the young lady I photographed earlier that evening (Photo #8).

 

As I left the venue, I recall thinking about the expression on the Media Coordinator’s face, who looked at me as if to say, “I can’t believe you DID that!”.

 

Come to think of it, neither can I.