Flash photography

by Quoc-Huy NGUYEN DINH - www.qhphotography.com

Introduction

1. A little bit of theory.
2. Different flash modes: manual / auto / TTL.
3. TTL or Manual?
4. On-camera / Off-camera TTL flash.
5. White balance?
6. Demo.
7. Hands on!

Different flash modes

Manual modes:

• Fixed full power, non adjustable
• Adjustable power settings: 1/1, 1/2, 1/4, 1/8 etc...

Automatic modes:

• A mode (Auto): controlled by the Flash only
• TTL (Through The Lens) mode (E-TTL, E-TTL2, iTTL etc...): controlled by the camera

A bit of theory - TTL & Manual

• 3 properties of light: direction, color, quality.
• Sync speed limited to your camera max flash sync speed: 1/200sec.
• Distance matters: the closer, the softer; the further away, the more even.
• Size matters: the bigger, the softer.
• Position matters: the direction and location of the flash determines the shadows' ones.

A bit of theory - Manual

• The flash light only cares about the aperture!
• The shutter speed only affects the exposure for the ambient light, but at high enough level can add to the exposure of the subject lit by flash.
• The ISO affects both ambient and flash lights.
• If the flash lit subject is too dark dial up, if too bright dial down. You can either dial up/down the aperture or flash power.
• Chimp and check your histogram to judge the exposure.

A bit of theory - TTL

• Focus points & metering modes can affect the TTL exposure calculation.
• The environment can and will affect the TTL exposure calculation.
• If the exposure calculated by the camera is too low, use the flash exposure compensation to dial up/down the flash power.
• Selecting a correct aperture/ISO will help your flash.
• Avoid shiny surface that will reflect the flashlight and fool the TTL sensor.

Auto modes - Pros and Cons

Pros:

• ease of use
• less hassle (sort of...)
• recent flashes/cameras have very decent auto technology
• no need for a light meter: less to carry
• great for fast paced events

Auto modes - Pros and Cons

Cons:

• limited on the technology
• lack of in-depth control
• can be fooled by the environment: non-consistent accuracy, repeatability
• hardware compatibility

Manual mode - Pros and Cons

Pros

• Consistent and repeatable results
• Full control on the exposure
• Great for creative shots
• Wider range of exposure compensation

Manual Mode - pros and cons

Cons

• Exposure calculation, test shots or light meter (not that bad actually)
• If distance flash / subject changes, exposure changes
• If aperture / ISO changes, exposure changes

On-camera TTL flash - pros & cons

Pros:

• practical.
• portable.
• accessible.
• less gear to carry.

On-camera TTL flash - pros & cons

Cons:

• not flattering light.
• light is coming from the camera's position.
• need a surface to bounce off of.
• limited choice of modifiers.

Limited choice of modifiers?

Off-camera TTL flash - pros and cons

Pros:

• control of where the light is coming from and thus control of the shadows.
• look more natural even without modifiers.
• can still bounce off surfaces.
• can use lot of different modifiers.
• open to more creativity.
• lot of fun.

Off-camera TTL flash - pros and cons

Cons:

• need for a light stand or a clamp or an assistant or hand holding the camera and flash.
• need a way to remotely trigger the flash units.

Off-camera flash modifiers!

About white balance.

• Recent flash and bodies support automatic white balance compensation.
• In difficult situations where lights have different colors, balance for the key light.
• You can use custom white balance if your camera supports it.
• If unsure, shoot RAW and set the WB to daylight.

Demo + Practical session

Let's have fun with the models!

How to expose for the flash?

Camera and flash are in Manual Mode. Tip: trials/errors and LCD/Histogram are your best friends.

1. Start at your lowest ISO for best image quality. But the following applies to any given ISO.
2. Set your shutter speed to your camera max flash sync speed (1/200 sec for most).
3. Set your aperture to any value, lets say f/8.
4. Take a picture and chimp. If the subject is to dark/bright, dial up/down the flash power. Alternatively dial up/down the aperture.
5. Repeat step 4 until satisfaction.

The histogram

How to balance the flash with the ambiance

This is a general approach to the technique, you can start with any aperture or shutter speed, just remember the max flash sync speed:

1. Set your ISO to the lowest value for highest image quality if you are shooting outdoor or in a bright location. Up this value if you are in a low light location.
2. Find the exposure for the ambiance. For this you can either use the camera metering indicator thru the viewfinder or take a shot in Aperture Priority and use the same settings back in Manual Mode.
3. Under-expose the ambiance by 2 stops, so when we'll bring in the flash onto the subject he/she will stands out.
4. Bring the flash in and get an exposure for the flash.
5. Chimp to verify your histogram and judge the flash/ambiance ratio.
6. Adjust the shutter speed if you want to change the intensity of the ambiance.
7. Adjust the aperture if you want to change the exposure for the flash. Then dial the same value to the shutter speed, in the opposite way, to compensate the ambiance.