Flash, on camera, off camera, synch speed, etc

This post is about using flash. I've got Nikon cameras, and shoot with 2 SB-800's but it should apply to just about any equipment.

Much has been written and discussed regarding flash already. Strobist ( http://www.strobist.com ) and the flickr group ( http://www.flickr.com/groups/strobist) have lots to offer when you begin to work on various levels of flash in your photography.

But there's a fear among some people about getting past just using the on camera flash, or a strobe mounted on camera. Hopefully this post will help explain some details for moving past that.


Like I said, I shoot with Nikon gear. I've got a D70s, D200 and a D300. Most of the follow will apply to the SB-600 or the SB-800. But realize the SB-800 comes with the stofen cap diffuser, and has some extra modes available.

Modes and Concepts

TTL / iTTL - TTL is the abbreviate for Through The Lens. All this means is that the flash is pre-firing, sending out a bit of light, and the camera is metering what got lit, how the exposure should be adjusted, and how much power the flash should output, to produce a good exposure.

Flash compensation - If all you have is the camera's build in flash. it's often tough to get a natural looking image. The flash is coming from right over the lens, it is often quite strong at close range. Note, most on-camera flashes (built in flashes) cannot even come close to reaching anything beyond 15 or 20 feet. But, one thing you can do is adjust the flashes "compensation" or the flash EV. Setting the flash EV to -1 to -2 is a great range of settings to go for. This will balance the natural/available light with the flashes output.

Note, when you've set the built-in flash's compensation, and then if you add a shoe-mounted flash (Nikon anyway), the compensation setting will be added (or subtracted) from mounted flash's output (sb-600, sb-800, etc). In other words if you set the on camera flash to -1 EV, and then mount a flash unit to the camera, TTL mode, and set it to -1EV, you're actually now shooting at -2 Flash EV. If you're using a dedicated flash unit be sure to set the on camera flash's setting back to 0EV. I've been burned by this before, trying to figure out why the flash's output was so much lower than expected.

Get the flash off the camera! (TTL cable) - One of the best things you can do to improve the light produced by a flash is moving it off the camera. There's just something that doesn't look natural or that good when the light is coming from right over the lens.

The easiest way to move the flash off the camera is to use a TTL cable. For Nikons this is the SC-29. It costs around 80 dollars, and you mount one end to the camera's shot, and the other end to the SB unit. Everything else works just like the flash was on the camera. You can set the flash to TTL, FP, or Master mode for example. With this setup, you can hold the camera in your right hand and the flash in your left hand and shoot and make adjustments as you go. Off camera flash will drastically change the result you get, for the better.

Nikon CLS - I think CLS (Creative Lighting System) generally refers to being able to remotely trigger flash units from the camera, and have them each behave differently, i.e. as you've set them) to produce a complex lighting setup. This can range from the camera and flashes entirely determining the proper output, to the flashes just producing the manually set output, or a mixture of both, triggered remotely, as a complete system/setup.


The way I tend to leverage Nikon's CLS is in one of two ways:
1) I use a flash or two set to a specific TTL EV settings, and let them pre-flash, and determine how much light to add to a photo/exposure.
2) I use a flash in commander mode (either built-in, or shoe mounted sb-800), and another flash set to manual remote mode at a specific output setting (1/8th power for example).

Flash Zoom Head Setting - The SB-600 and SB-800 has a flash head that can zoom to project light wider or narrower depending on the lens's zoom amount. This will happen automatically if the flash is mounted to the camera, as you zoom a lens the flash will zoom to send light to just the part of the scene seen by the lens. While this is great, you can also set the flash zoom setting manually.

With the stofen cap mounted, the flash will automatically change the zoom setting to 14mm. With the diffuser panel dropped in front of the flash head, it will change automatically to 12mm (I think).

But, with the flash off camera in remote mode, you can gain some control over the flash by setting the zoom mm manually. You can use a remote flash set to 90mm and positioned to just light a person's face for example, instead of letting it be at a wider setting automatically. A leap you can make is to control the flash zoom head's setting and distance from a subject to gain more control.

SB-800 Reset - If you played around with the settings on your SB-800 or SB-600 and need to reset thing, you can just hold down the Mode and the Power buttons for a few seconds and it will blink and will reset the settings.

Remote flash channel and group - D70, D70s, D40 ?, D50 ?, D60 ?, D80 ?, I think for all these cameras you need to set the remote flash to Channel 3 and group A. With the D200 and D300 you can set both the channel and bank and configure settings for a tons of flashes in a few groups.

FP mode and Flash Sync Speed - FP mode stands for Focal Plane mode. To understand what this is, you need to understand how the shutter works. When you take a picture with an SLR, there's a front curtain and a rear curtain. To expose film or the digital sensor, first the front curtain opens exposing the "film". Then approximately when the shutter duration is reached, the rear curtain raises and blocks further exposure. At slow shutter speeds there's a long period of time when the "film" is exposed. When shutter speeds are very fast, the two curtains are moving at the same time for some part of the exposure. In this case there's a limited "window" or opening where light is coming in, and it's moving across the "film".

To understand how this relates to flash, realize that normally flashes fire very fast. A flash can fire anywhere (roughly) from 1/250th of a second to 1/10,000th of a second. When the shutter speed is 1/100th of a second, there's more than enough time for the flash to fire and do its full output in less time.

But, if you want to shoot at 1/500th of a second and add flash, generally it won't work. The Nikon D200 and D300 have a sync speed of 1/250th. So, that's the max shutter speed you can get when adding flash. At faster shutter speeds the problem is that the two curtains are moving at the same time, and the flash is so fast that only part of the "film" is exposed during the flashes very fast output. To overcome this limitation, the camera can be set to flash-sync mode of 1/250th FP-mode. What this does is enable higher flash sync speeds. The way it accomplishes it is by moving the curtains the same way, but the flash emits multiple bursts of light in order to add flash across the entire exposure, as the curtains are moving. You won't likely be able to see it with the naked eye, but the flash will fire tens of times for example at 1/1,000the of a second exposure when in auto-FP mode.

I first learned how to use remote flash with my SB-800 and D70s from Ken Rockwell's site. While many people have harsh opinions regarding his site and views, I have a new found appreciation for what he writes, after trying to write a few guides from scratch myself... You can see his flash guide here: http://www.kenrockwell.com/nikon/flash.htm

-Jon

Flash, on camera, off camera, synch speed, etc