Hot-Shoe Flash Primer
Indoors - Single Flash

Single flash indoor photographs are dreadfully flat. Adding a bracket and diffuser improve the lighting somewhat, but it is still flat and provides very little subject / background tonal separation. Separation is important because that contrast is what will lead the eye the center of interest. Just about any flash can perform this task.

Manual flashes require the photographer to manually calculate distance to the subject and adjust the aperture as needed per the guide number or chart/dial indicator on the flash, or a flash meter reading. Shutter speed is limited to the x-sync speed of the camera (typically 1/200 or 1/250th).

Semi-automatic Thyristor flashes use a photocell in the flash unit to control the flash duration / output. The camera is set manually to a single f/stop (e.g. f/8) and then as the photographer changes his distance to the subject the flash compensates by adjusting the output. Exposure is based on the reflected light the flash sensor sees, so it must be pointed in the same direction as the camera. Since is sees a wide average it may not be accurate when used with telephoto lenses. Shutter speed is limited to the x-sync speed of the camera (typically 1/200 or 1/250th).

Fully automatic TTL flashes utilize feedback from the camera's settings and metering system to control the flash duration / output. The connectivity allows the use of auto exposure modes (P, Av, TV) and adjustment of the flash (FEC) to compensate for scenes with less or more than average middle gray reflectance. Because the camera meters what the lens sees a TTL flash will more accurately meter the scene regardless of the focal length used. Most linked flash systems automatically zoom the flash head as focal length changes to put the maximum amount of light in the field of view of the lens.

Outdoor Fill Flash

The range of brightness in a typical outdoor scene or a subject standing with their backs to the sun exceeds the range a digital camera can record. In recording for highlight detail shadow detail will be lost. Light from an on-camera flash can be used to add light and fill the shadows. For a natural look the fact flash has been used shouldn't be obvious. This requires modifying the flash with a diffuser so it is soft and as shadowless as possible and keeping it above the lens where any shadows it does create will not be distracting. Natural looking fill flash also requires precise balance of the flash output with the ambient light.

Manual and Thyristor flashes are limited to the x-sync speed of the camera (e.g. 1/250th) which would require an f/stop of f/11 on a sunny day shooting at ISO 100 (Sunny 16 rule-of-thumb). f/11 requires a great deal of flash power to match and DOF at that aperture makes separating a subject from the background using wide apertures impossible.

Some TTL flashes support high speed flash mode which overcomes the x-sync limit by pulsing the flash as the shutter curtain slit passes over the camera sensor. Light output is less than normal mode, but very short shutter speeds can be used for outdoor fill flash at wide apertures. The creative value of HS flash in fill-flash situations should not be underestimated. I would not by a new flash without it!

Dual Flash

Adding a second off-camera flash provides modeling and subject / background separation. The subjects appear three dimensional and project from the darker background. The off camera flash creates eye catching highlights which led the eye to the faces and distractions in the background fade into the shadows because the on camera flash, now used in a fill role, outputs less light. Manual, Thyristor, or TTL flashes can be used in dual flash configurations.

Off camera manual and thyristor flashes will need to be triggered with and optical or wireless device. Optical triggers work fine if there are no other flashes going off nearby. Multi-channel wireless triggers will allow control of the lights when others are shooting nearby. Most high-end TTL flash systems incorporate wireless control via infrared or pulsed "pre-flash" signals.

Lighting ratios are controlled with manual flashes via power setting and distance from the subject. For example, two identical flashes at equal distances will produce a 2:1 reflected highlight:shadow lighting ratio of a face. Placing the key/fill (on camera) lights at any of these distances combinations will produce a 3:1 H:S ratio: 16ft/11ft, 11/8, 8/6, 6/4.

Lighting ratios with Thyristor flashes can be controlled by using the flash sensors, but since the off camera flash sensor does not see the same view as the camera the manual method above produces more predictable results.

Most high-end TTL flash systems (e.g., Canon 580ex, 550ex, 430ex, 420ex) allow the setting of ratios via the master unit on the camera. Prior to the actual exposure the camera will fire a sequence of pre-flashes, first to determine the scene reflectance, and then to transmit the control signals to the flashes. The ratio settings and nomenclature used for Canon flashes does not conform to the conventional reflected H:S ratios used to describe studio lighting. It is necessary to perform tests at various ratio combinations.

Check the index for separate tutorials on Dual Flash Candids and Lighting Ratios and Meter Readings

Using more than two flashes

Hot-shoe flashes can be successfully used in combinations of 3 to a dozen, but consider that the reason one would think of using more than one flash is creative control of the scene which is photographed. Unless portablitity is the most important factor lighting scenarios requiring more than two lights are generally better done with studio lighting systems which have modeling lights and allow the use of a wide range of modifiers. I mention this as a caveat so you'll stop and think before buying that third $300 - $400 TTL wireless flash whether a $250 studio light might be a better start to meet your long term goals for lighting.

Tips on flash technique

The keys to effective single source lighting is to make the light diffuse and control the direction of the shadows it casts. There are a great many techniques you can use with single and dual flashes. No one of them is ideal for every shooting situation so its best to be equipped and experienced to utilize all of them. Below are some of the possibilities. Try everything, find what works best for you in terms of results, convenience, and cost.

Ceiling Bounce: Bounce off the ceiling is the simplest approach, but you need to watch the angle the bounced light is striking the subject. If you get too close to the subject and the bounced light comes straight down the brow will shade the light and you'll wind up with a bright forehead (closest to the light) and cheeks (next closest) with dark eye sockets in between. That little card that pulls out of the flash is to create reflective catchlights in the eyes when you bounce off the ceiling. There are many commercial devices such as the StoFen which bounce most of the light off the ceiling, but some of it forward. You can accomplish the same thing by simply attaching a 5x7 or larger white card to your flash with a rubber band.

Wall Bounce: Another bounce approach is to use a nearby wall as the bounce surface. You use the tilt and swivel to aim the flash at the point on the wall where you'd put a softbox is you had one so the diffuse light will bounce at a sideways angle. The flash will automatically zoom to 50mm when you tilt the head to bounce but its more effective to manually zoom the flash out to its maximum zoom so the spot of light you put on the wall is as bright and intense as possible. The smaller the spot of light on the wall is the more directional and controlled the reflected light will be. When you use this side bounce technique you need to be aware of where the nose shadow is falling on the face. You want the light to strike from a downwards direction so the nose shadow falls downward, not sideways into the far eye. Aim the light towards the direction the subject is facing and shoot into the shadow side for the best 3D modeling of the subject.

Umbrella Bounce:Bouncing into an umbrella is similar in concept to the side wall technique. But to do it you need a means to trigger the stand mounted light and a bracket to hold the umbrella and flash. Triggering for the Canon TTL flash system can be done via a ST-E2 trigger (about $200) or and extension TTL cord. The standard TTL "extension cord 2" Canon sells is only 2' long, but some have cut it, added connectors, and extended it with Cat5 or Cat 6 wire. If you don't want to modify the cable yourself custom made extensions are available from You can find a bracket to hold the flash and umbrella at B&H.

The ST-E2 controller seems like a logical solution at first glance, but there is a better long term approach. The ST-E2 costs about $200 and can only control two groups; A:B. It uses infrared signals which have a limited range. Most people wind up getting a second flash to have key and fill lights. B&H sells the 580ex for $379 (Early 2006). It will serve as the Master for the 430ex and control 3 groups A:B ratios, and power settings for group C. It uses visible light to send the control signals and has a greater useful range than the ST-E2. Thus if you look at the long-term growth strategy for your lighting buying a 580ex is a much better investment than the ST-E2, because you will inevitably by the ST-E2 then a second flash.

Brackets: The biggest drawback of camera hot shoe design is the fact the flash winds up even with the lens when in portrait mode which creates unflattering and distracting sideways shadows. The solution to this problem is to use a camera bracket which keeps the flash above the less at all times. You want it at least 10-12 inches above the len so the direction of the light is always downward relative to the nose of the subject. The use of a bracket makes direct flash photos more attractive. They will still have harsh shadows, but those shadows will be in places which are not seen or are less distracting. For example the head shadow will fall out of sight down behind the shoulders and the nose shadow will fall directly under the nose, helping to hide the nostrils (if you keep the camera above the subject's eye line).

Brackets + Reflecting Diffusers: The better positioning of the flash in portrait mode created by a flash bracket makes the use of direct diffusion methods practical. Instead of bouncing most of the light off the ceiling you can bounce all of it forward with more efficiency and control. That's the approach I use in most situation and I've made my own diffusers. The advantage of the direct-diffused approach vs bounce is that it works the same whether there is a ceiling or not; indoors and out. That consistency makes the lighting it creates predicable and predictiblity makes it controllable. Commericial mini-softbox products produce the same style of lighting; bouncing all the light forward rather than relying on external bounce surfaces. The Canon TTL extension cable 2 (about $50) is needed when using a bracket to retain the TTL control of the flash

Even when a dual or multiple hotshot flash lighting scenario is used, a flash mounted on a camera bracket with a reflection-diffuser will be a good source of nearly shadowless fill.

Holistic Concepts for Lighting
and Digital Photography

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You can contact me at: Chuck Gardner

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