Camera flash pulses are typically very fast. It is fast enough to freeze motion even if you use a very slow shutter speed as long as the light from flash dominates the exposure.
Most camera flashes have xenon flashtubes. It lights up when the charge stored in a capacitor is discharged through xenon gas. The xenon gas is not very conductive in its normal state but its resistance can be greatly reduced when the xenon gas molecules are ionized, ignited by a high voltage pulse. The charges stored in the capacitor start to flow through the tube, giving out a very bright light. As the charge stored in capacitor discharges, the light intensity decreases.
The light intensity during a flash pulse isn’t constant. The light intensity emitted from the flash tube rises to a maximum quickly then fall off. If the charges stored in the capacitor are allowed to completely discharge, the light intensity will show a graduate reduction tail. Since we don’t want full power flash for each shot but rather just the right amount of light for proper exposure, the flash unit cuts off the discharge circuit at different times to control the amount of light emitted. Lower flash output power means shorter flash duration. Read More…
Posted in
Flash photography on January 26th, 2010.
No Comments.
The flash output level of a Nikon SB-600 Speedlight Flash
can only be set to the minimal of 1/64 in manual mode. That leads many people to speculate the minimal output from the flash is 1/64. If you have used the Nikon Creative Lighting System (CLS) Advanced Wireless Lighting (AWL), you will know that you can use 1/128 output setting on the wireless commander unit. The wireless commander can be the built-in flash of your camera, or SU-800 commander, or SB-800/SB-900 Speedlight flashes. The question is what happens when the remote flash is a SB-600. Will it actually output 1/64 or 1/128 of light when the commander tells it to do 1/128?
To answer this question, I ran a test with a flash light meter to measure the output of the SB-600. Read More…
Posted in
Flash photography,
Q & A on January 20th, 2010.
2 Comments.
The question got asked quite often on the internet lately. Is it possible to mix TTL Flashes with non-TTL manual power flashes or strobes so they sync together? For example, one guy wanted to fire two SB-900s in wireless TTL mode while also triggering an Alien Bee studio strobe at the same time.
The answer is Yes. Since I have only Nikon DSLR and Nikon Speedlight flashes (D200, SB-800, and SB-600), I can only describe what’s possible for people in similar situation. For your particular Camera/Flash brands you will need to decide if this method works for you. Read More…
Posted in
Flash photography on January 4th, 2010.
2 Comments.
In the previous post about front-curtain and rear-curtain sync modes, I used a two-exposure model to describe the final image created by the contribution of both ambient and flash lights. In this post, I will go into details about the shooting parameters that affect both exposures and the most effective techniques of balancing flash and ambient exposure. I will mostly speak in Nikon terms since that’s the only brand of DSLR camera I have access to.
Four parameters
The four camera parameters that affect the final exposure are: ISO, aperture, shutter speed, and flash output amount. If the camera and flash are in full manual mode, all four parameters can be freely adjusted by the photographer. In the chart below, a check mark is used to indicate that the particular camera or flash parameter affects ambient or flash exposure. “–” means it does’t. An important assumption is made here: Flash duration is so short compared to shutter speed that shutter speed does not affect flash exposure. This excludes the FP high speed sync flash mode from our discussion to avoid complications. Read More…
Posted in
Flash photography on January 1st, 2010.
2 Comments.
In the article titled Understanding Flash Sync Speed, I discussed in details how focal plane shutter works and what maximum sync speed is. What was left out was the two different flash sync modes: front-curtain vs. rear-curtain sync.
In front-curtain sync, the flash fires immediately after the first (front) curtain opens completely; in rear-curtain sync, the flash fires just before the second (rear) curtain starts to close. To understand the differences they make, let’s use a simple two-image model.
The image sensor continuously capture the image formed by the lens on the sensor surface when the shutter is open. There is one image captured by the camera in each exposure but you can imagine the sensor captures two images: one image formed by ambient light and one image formed by the flash. The two images are then superimposed together. In front-curtain sync, the flash image is captured first followed by the image of the ambient light; while in rear-curtain sync, the flash image is captured after the image sensor captures the ambient image. Read More…
It is not the safety of the photographer but the safety of the camera at stake here. Some flashes use very high voltages in the trigger circuit that may be high enough to fry your camera’s circuit board. If you are temped to buy cheap flashes from garage sale or off eBay to expand your strobist arsenal, check this site first to make sure it is safe to use on your camera or other triggering devices’ hotshoe.
If the flash you are interested in is not listed, you can follow the instructions (scroll down until you see How to Check the Trigger Voltage) to measure it yourself. My Starblitz 200 DNX isn’t listed in there. The voltage on the sync terminal is ~11 volts. I put it on my Nikon D200 and it works just fine. According to Nikon D200 manual, the accessory shoe on the camera can support up to 250 volts.
Nikon USA Learn & Explore learning site has posted some really nice video tutorials in which Joe McNally brings you on location and shows you how to control the color in flash photography. The video tutorial has two parts:
In this set of video tutorials, Joe brings you to Good Springs, Neveda, a ghost town. You will learn from Joe as he steps in a historical place called Pioneer Salon and goes through location assessment and the actual shooting process. The success criteria of location photography is that the photos should be able to capture the mood of the environment and invoke feelings in people who sees the photos even though he/she may be millions of miles away. The focus of the tutorial is about achieving such goals by the choice of color and control of color. Read More…
Nikon CLS Advanced Wireless Lighting is actually very capable. It handles all the functions you can do with a Nikon Speedlight attached to the camera’s hot shoe except the RPT flash. Specifically, Flash Value (FV) lock, FP high speed sync, modeling flash all work seamlessly. It even works when you use mirror-lockup function on the camera. In the part V of the series, we will look at the FV lock function.
Flash Value (FV) Lock
When you push the FV lock button (on my D200, I assign the FUNC button to FV Lock), the camera will initialize the pre-flash sequences to determine the flash output amount for all groups involved. Then you can recompose and take a photo without causing incorrect exposures for off-center subject. This is fairly straight forward in regular TTL flash mode but more complicated in wireless lighting setup due to the extra communication requirements. To illustrate the flash sequence when FV lock is used in Advanced Wireless Lighting, I use a simple example in which Master (a Nikon D200 in Commander mode) is set to TTL mode and remote group A is also set to TTL mode. I first pressed the FV lock button, then pressed the shutter release button all the way down ~1 second later. Read More…
Posted in
Flash photography on December 1st, 2009.
4 Comments.
