dante stella stories photographs technical guestbook

Davidde, I've read the same line nine times.  What do you want?
 
Fill flash for amnesiacs!
 

This article is primarily written for my brother, who cannot seem to remember these rules, no matter how many times I explain them. You can read along for kicks, since there does not seem to be any other systematic discussion available anywhere. This is organized by what type of camera and flash you have, so look at the headings until you see something like yours. 

Fill flash is typically used to correct for a backlit subject - or one with shadows that are too deep.  And by eliminating some (or all) of the shadows in a scene, fill flash can make the dynamic range of a scene manageable.  That's why point-and-shoot cameras love to fire the flash - and why the "ok" rate with these cameras is embarrassingly high compared to what you might see from a sophisticated user who has nothing but disdain for strobes.  Fill flash can also be abused; in daylight scenes, you might want less of it.

In this article, sections 1-6 cover basic fill flash; sections 7-9 cover some variations on these techniques.

1. General principles governing fill flash

The following are basic principles which limit fill flash. Don't ask why these limit you; if you do enough experimentation you will know exactly why. If I save you the trouble of working these out, I hope you excuse the fact that I am not going to explain the "whys." None of these is a show-stopper, but the more rules you obey, the broader your range of fill flash possibilities.

a. Slow film is better than fast film.

b. Fast shutter maximum synch is better than slow. 1/125 is practical minimum; 1/60 is close to useless.

c. Never set a shutter speed faster than the maximum flash synch. So if your camera has a red 1/125, do not set it at 1/250.  If you do, you'll end up with half-underexposed pictures.

d. A closer subject distance is better than far.

e. A leaf shutter is better than focal plane, if for no other reason than it synchs at all speeds (in many cases up to 1/500 sec or more).

f. More powerful flash is better.

g. More flash auto modes are better. Or more power factor modes.

h. You cannot do it predictably in program mode.

The beauty of fill flash is this: almost any flash can be for the purpose, provided that you have aperture control on the camera and have an idea of the flash's guide number (or if it has automatic operation).  It never hurts to have more power in the flash, more auto modes on the flash, more manual power factors, or more ability to change the camera exposure.

Something like a Nikon SB-800 is the prototypical "good" (though expensive) fill flash.  It has a guide number of 125 in feet at ISO 100 (making it fairly powerful), it has manual modes down to 1/128 power, and numerous automatic modes.  So is a Metz 45CL-3, which is even more powerful.  At the low end of a good fill flash is something like a Nikon SB-20 or a Vivitar 283.  But you can do fill flash even with a $15 Vivitar 2800 that you bought on Ebay.

2. Any camera with a manual flash

In a perverse way, this is the easiest way to do fill flash, because manual flash does not care about how reflective the subject is. Learn the guide number of your flash (feet or meters is unimportant, but you have to use the same unit of measure for all steps). Focus the lens and note the distance (same unit as before). Divide the guide number by the distance. This gives you the aperture. Then meter the overall scene. Set the shutter speed that corresponds to this aperture for the overall scene. If you have to set a shutter speed above the maximum synch speed of your camera, you can't use fill flash.

Example:

a. Flash Guide Number is 30 in meters.

b. Subject Distance is 5 meters.

c. Aperture (based on flash) = 30/5 = ~5.6

(This far will produce accurately exposed flash pictures against a dark background)

d. Measure overall exposure and select shutter speed based on flash aperture. F/5.6 and 1/125 (other choices were f/4 and 1/250; f/8 and 1/60; f/11 and 1/30)

Leaf Shutter: It is worth noting that this technique works a lot better with cameras with leaf shutters that synchronize at up to 1/500 sec. With a leaf shutter, you can fill-flash in daylight with 100-speed film.

Half-Power Fill: If the flash has a half-power setting, simply select it. If the flash does not, pick the aperture/shutter combination that has the aperture one stop smaller than what the computation wants. For example, if the GN/distance dictates 1/125 and f/16, select 1/60 and f/22.

3. Any camera with an automatic flash

An automatic flash is a great aid in doing fill flash, and it greatly simplifies things. First, set exposure for the background scene, using any shutter speed at or slower than the maximum synch speed. Next, choose an automatic mode on your flash that (a) matches your distance and (b) is one of the combinations that matches the background scene.

Example:

a. Flash has automatic modes of f/2-f/16

b. Background exposure is 1/125 and f/16 (other choices were 1/60 and f/22; 1/250 and f/11; 1/500 and f/8; 1/1000 and f/5.6)

c. Set flash to f/16 mode (provided your subject is close enough)

Leaf shutter: If you have a leaf shutter camera, in the example above you could also select the aperture to f/11 (with 1/250 sec) or f/8 (with 1/500 sec) as well, selecting the appropriate auto mode on the flash. Some flashes have one auto mode, some two, some more. The Nikon SB-20 I use has 8, ranging from f/2 to f/8 with 100-speed film.

Leaf shutter with LVS/EVS: If your camera has a system which can lock the shutter speed and aperture rings together (like the Rolleiflex 3.5MX-EVS, a Kodak Retina IIC, etc.), you set the background exposure and to switch both aperture and shutter speed, you just turn one dial. This lets you cycle through the shutter speed/aperture combinations much more easily and as far as I know is the only good use for the LVS/EVS system.

Half Power Fill: pick an aperture/shutter speed that is one f-stop smaller than the flash mode you are using. So if the background exposure is 1/125 and f/16, pick the flash auto mode for f/11.

4. Aperture-priority camera with an automatic flash

Aperture priority follows the same basic rules as manual, but you have to watch the shutter speed, which cannot be allowed to get higher than the maximum synch speed. Let the camera meter the scene. Rotate the aperture dial until you get a shutter speed within the synch range. Set flash to automatic mode dictated by the aperture you selected.

Example:

a. Flash has automatic modes of f/2-f/16

b. In this example, background exposure is 1/125 and f/16 (other choices were 1/60 and f/22; 1/250 and f/11; 1/500 and f/8; 1/1000 and f/5.6)

c. Set flash to f/16 automatic mode

Leaf shutter: If you have a leaf shutter camera, in the example above you could also select the aperture to f/11 (with 1/250 sec) or f/8 (with 1/500 sec) as well, selecting the appropriate auto mode on the flash. Some flashes have one auto mode, some two, some more. The Nikon SB-20 I use has 5, ranging from f/2 to f/8 with 100-speed film.

Half Power Fill: Pick a flash auto mode that is one f-stop larger than the aperture you have selected. So if the camera is set to f/16, set the flash auto mode to f/11.

5. Shutter-priority camera with automatic flash

Aha! Now this is a tough one. Set the camera to the maximum shutter synch speed (typically 1/125 on these cameras). Let the camera pick the aperture. Choose the automatic mode on the flash to match.

Example:

a. Flash has automatic modes of f/2-f/16

b. It's a sunny day. You set to 1/125 sec; the camera sets the aperture to f/16.

c. Set flash to f/16 automatic mode

Half Power Fill: pick a flash auto mode that is one stop larger than the aperture the camera has selected. So if the camera picks f/16, set the flash to the f/11 mode.  For quarter-power, set the flash to the f/8 mode

6.  TTL flash

There is not a lot to say about fill flash with TTL.  I've always wondered how it works in film cameras, since the reflectivity of film emulsions (where the TTL sensor reads) is not very uniform across brands and types.  But I digress.  If your camera and flash lack TTL exposure compensation, you can do full-power TTL fill flash, and that's about it.  The metering pattern will be more central than with an automatic flash (because the sensing area in more primitive TTL systems generally is the center of the film, rather than an area in the top 1/3 of the frame that is seen by a sensor on the flash body).

Things get better if your flash or camera has exposure compensation for flash.  If both do, be sure to read the camera manual to see which compensation (the one on the flash or the one on the camera body) predominates.  It is also good to figure out the metering pattern being used for the TTL functionality.  And it pays big dividends to learn whether the regular (non-flash) exposure compensation control still works when using flash.  I won't name any names, but some older cameras completely ignore the ambient exposure compensation when TTL flash is being used. 

TTL flash is not bad for fill, but it has some of the same defects as automatic flash, namely, it can be fooled by subject reflectivity.  This is mitigated in systems like D-TTL, E-TTL, i-TTL, and M-TTL, which preflash the subject and take a reading.  The only nit with these systems is that the preflash sometimes is visible to the subject.

7.  Bounce flash

Some people like to take things a bit further by adding bounce to one of the fill techniques described in Sections 1-6.  Bounce with a handheld camera is very difficult to do except with an automatic or TTL flash (if you are using a manual-only flash, consider metering at the subject with an incident flash meter).  Part of the problem is that ceiling heights and reflectivity vary.  The nice thing about bounce flash is that if done correctly, it looks very nice, with few or no shadows visible in frame. 

Bounce flash works best with (a) flashes that have tilt heads; (b) flashes with high guide numbers; (c) reflection surfaces of neutral color (like bright white); and (d) a reasonable distance from camera to subject to background.  The tilt head - rather than a tilt bracket - is important because you want the flash's auto sensor pointing toward the subject and not the ceiling.  The high guide number is necessary because you are not making the light travel in a straight line to the subject; rather, it is following two sides of a triangle.  This is a much longer distance, and the intensity of light falls off exponentially as distance increases (double the distance, one-quarter the intensity).  The reflection surface should be a neutral color so as not to create a color cast on the subject.

The rules of half-power flash apply here.

One variation of bounce flash is tilting the head up and using a bounce card to diffuse the light before launching it at the subject.  This automatically costs flash power but in most instances makes the light more flattering on the subject.  Another is to use a Sto-Fen-style diffuser (opaque rigid plastic diffuser that snaps onto the nose of the flash) or a Gary Fong diffuser (like a pearlescent clear plastic bowl).  All of these fit into the subcategory of using bounce and diffusion simultaneously.

8.  Off-camera fill flash

Off-camera flash is also popular.  This requires the flash to be cabled to the camera either with a PC cord or a full-TTL-shoe passthrough (see Nikon SC-17).  The off-camera flash is often put on a flash bracket or held in the hand.  Brackets are a bit more comfortable.

A simple PC cord will work for non-dedicated automatic flashes.  Unless you use one with a locking function (screwdown or bayonet), it may pull out of the camera.  The only issue with using a PC cord is that when handheld, the sensor will not be looking at the subject from exactly the same angle (and in most cases distance) that the lens is.  You can get around this with a remote sensor mount (like on the Vivitar 283, which has a special cord that sits in the flash shoe and to which you stick the flash sensor - the cord then plugs into the sensor jack on the flash).  Some flashes have separate remote sensors like the Metz Mecamat for th 45 and 60 series.  The Mecamat is a fearsome device and possibly the most elaborate remote sensor ever made: two spot-metering sections (with popout viewfinder), twin calculator dials for manual and automatic modes, and parallax correction for closeups.

Using a full-TTL-shoe cord will give you some additional functionality like the ready light in the viewfinder and automatic synch speed setting (for dedicated flashes) and, if desired, TTL operation.  It also has the benefits of being more difficult to dislodge from the camera in handheld use.  If you use TTL, the flash sensor (i.e., the camera) will always be pointed at the subject.

9.  (Bare) bulb fill flash

If you ever wondered why old pictures are always in focus, even though film was slow and lenses were slow, here's the answer: bulb flash.  Back then, flashbulbs were made of magnesium foil in a light bulb filled with pure oxygen.  As you can imagine, it was a very bright flash.  In fact, even the "small" flashbulbs could easily hit guide numbers of 300 with 100-speed film - in other words, many times more powerful than the typical electronic flash today.  Back then, the guide number of a flash depended in part on the shutter speed of the camera because the flash had a rising (and then falling) brightness as it burned.  Depending on how much of this was caught by the shutter's being open, that much illumination would hit the film.  And in the end, result was that Speed Graphic cameras shooting huge flash bulbs could be stopped down to f/32, pretty much obviating any focusing.

Even after flash bulbs fell out of favor, people really liked the flash from round and oval reflectors, hence the Honeywell Strobonar space-age electronic flashes (oval reflector assembly) and newer electronic "bulb" flashes like the Sunpak 120j and the Quantum Q-flash.  Some people like to take this to the next level by not using a reflector, i.e., making it a "bare bulb."  The light from a bare bulb flash radiates in all directions, simulating a super-powerful bare light bulb.  This has all of the same benefits of bounce flash - plus more indirect light hitting the subject from surfaces other than the ceiling.  The light is less directional, but it has a cost: unlike situations where there is a reflector, light can also go away from the subject. 

This, too, is a mode of fill flash that greatly benefits from an automatic flash, a TTL flash/camera setup, or the use of an incident flashmeter at the subject.

Conclusion

As Dirty Harry says, "A man's got to know his limitations." The best fill flash system ever made was the Konica Hexar AF, a camera which makes two exposures in P mode - one for the background measured by ambient light, and one for flash, measured by focused-subject distance. It knows how to balance these. Nifty!

DAST