Saturday, July 19, 2008

Camera Sync Speed and Flash

There seems to be a fair bit of confusion in the world about camera sync speeds, Pocket Wizards, and high speed sync so I thought I would try to explain and demonstrate how it all works.

Camera Sync Speed (SLR)
Your camera has a set sync speed which is the fastest shutter speed you can use with a flash for that particular camera. So say the camera companies. Knowing how it works can allow for some additional creative processes. I'm going to assume that you know what a shutter is, and the examples here were shot with a Nikon D2Xs, Canon's work the same way, they both have vertical focal plane shutters. Rather than rewrite what's already been written about shutters I'll refer you to a fairly good description with diagrams on wikipedia.

The sync speed of your camera is the maximum shutter speed at which the shutter is entirely open. After that point the shutter begins to close before it is fully open, creating a slit that moves across the focal plane as can be seen in these shots below.

"Wait a minute you're saying, how did you shoot faster than the sync speed of the camera, mine won't let me do that!"
Most SLR and DSLR cameras detect that a flash is attached and electronically limit the shutter speed to the maximum sync speed of the camera. By using a PC cord or a Pocket Wizard or other such remote you can bypass the detection of the flash. If the flash is not on the hot shoe, the camera doesn't know that it's there, and thus it doesn't limit the shutter speed. This can be a good thing if you understand how to use it. As you can see in the images above there is very little difference in the 1/250 shot and the 1/320 shot, if I'm shooting with pocket wizards I frequently shoot at 1/320. Even at 1/500 the flash still covers almost the bottom 2/3 of the frame, so if I position my flash lit subject in that bottom 2/3, and keep the top 1/3 lit by ambient light, everything will be fine. You can use the same trick for vertical shots as well, just keep the flash cropping in mind when you compose.

Pocket Wizard Multimax Fast Mode
The Pocket Wizard Multimax transceivers have a fast mode that according to the manual allows you to sync up to 1/1000 of a second. Of course that's dependent on your camera's sync speed, and the only camera I know of that can sync at 1/1000 is a Rollei with a PQS lens. It does affect your camera's sync however, as shown in the photos below. The photos with the HS are the ones shot in Fast Mode

As you can see from the images, with Fast mode on the Multimax there is no discernible flash cropping at 1/320, and at 1/400 you still have most of the frame available for flash. At 1/500 and 1/1000 there is a smaller difference, but still good to know about. Please note that every camera is slightly different so you should repeat this test with your own camera before you start using it this way.

Nikon Auto FP High Speed Sync
As I use Nikon Cameras I won't go into the Canon version of this feature, although i believe it is similar. Nikon pro cameras and the newer Nikon "prosumer" cameras allow you to use what they call "Auto FP High-Speed Sync" mode with the Nikon SB600 and SB800 flashes. It allows you to shoot up to 1/8000 with a flash. It accomplishes this by firing a bunch of vey fast flash pulses instead of one single flash, and these pulses blanket the shutter as it opens and closes so that the entire image is lit. There are several benefits as well as several drawbacks to this feature.
Benefits - As it allows you to shoot at a higher shutter speed you can adjust the ambient light level and keep a lower aperature even in bright daylight. Also you can shoot at a higher shutter speed to freeze action and still use fill flash.
Drawbacks - Because it fires a bunch of flashes the actual flash "duration" becomes much longer making it less than useful for freezing action between 1/250 and 1/1000. Also because it has to fire more than once the effective power level of the flash is greatly reduced, and the recycle time increases. The biggest drawback is the huge reduction in output. My Nikon SB800's at ISO100, 1/2 power, 70mm zoom at @7 feet give me @f8. With the same settings using Auto FP high speed sync I get less than f2.8 Even at full power I get less than f2.8 Not great if you need to have the flash more than a few feet from your subject.
Also this is a feature that is enabled on the camera, not the flash, so it won't work with Pocket Wizards, although the new Radio Popper wireless TTL system will probably work fairly well with it.

I'll follow up with review of this feature with the Radio Poppers once I get a set, hopefully fairly soon.

Saturday, July 5, 2008

Seeing things. Light - part 1

A lot of people over the years have asked me to critique their photos or help them with things like lighting. I always get asked about what I think is the most important thing to learn about photography, or "how can I become a better photographer?"

I usually respond by talking about spending time learning to see things. A photograph can be brought down to two basic elements, light and composition. There are other things that contribute to a great photo as well of course. Things like color and timing and focus etc. but really it comes down to light and composition.


By light I don't mean how well you use flashes to light something, I mean the overall light. A photograph is light traveling through a lens and hitting film or a sensor for a brief moment of time. That light usually comes from a certain direction and is filtered by various things that diffuse it or obscure it or make shadows out of it. If it isn't diffused it is much brighter on the side that the source is on, and darker on the side away from the source. Highlights and shadows. Our eyes see it all and in combination with our brain interpret it so that we see light and shadow mostly as one. When you look at a photo you don't interpret it the same way you do the surrounding world. It is flat, two dimensional, and it's not moving. It is a frozen slice of time and the differences between light and dark are far more noticeable. The way light strikes an object is far more noticeable as well. When you are taking photos, one of the most important things you can do is learn to see the light that is actually happening as you are shooting. And learning to see it the way it will look in a photo. Practice this. Take the time to look at the way light is happening. Walk around and look at objects front lit and side lit and back lit. See the differences. Take photos of things from 3 different angles so you can see the difference in your photo. Look for interesting shadows or highlights. Practice seeing the light.

More to come including examples in part 2 on light.