Sync Speed

3Aug/117

Shooting with flash is a bit different to shooting with out flash. The key part of determining any flash exposure is the lens’ aperture, the camera ISO, and the power out put of your flash. The exposure happens when the flash fires and your shutter needs to be open for the duration of the flash.

The duration of the flash from electronic flash units is quite short, about 1/1000th of a second or even faster is not uncommon. The exposure is made while the shutter is open, and the flash fires. Your cameras shutter speed will be slower that the flashes there for you freeze that moment in time. In short the shutter opens, the flash fires, and the shutter closes. The amount of light that get through to your chip (or film) is determined by the power of the flash and the F/ (aperture) used. Finally the ISO settings of your camera will determine how much of that light it keeps or can use.

If you are shooting at a higher shutter speed than your camera can synchronise at you will only get part of the picture. What part is missing depends on which way the shutter travels and how much you get is determined by the shutter speed you selected. If your shutter speed is set way to fast you will only get a black frame, if your sync speed is set only slightly to fast you will get a black stripe on the side of your photo. Modern DSLR cameras have maximum synchronization speed that varies with each camera so please look at your cameras hand book to find out the maximum sync speed (or X speed)

There are several different affects you can achieve by adjusting your sync speed. Lower shutter speeds allow more of the ambient light to influence overall exposure, mostly the background (because the aperture you select determines the main subject’s exposure). Using a slow shutter speed can "open up" the background allowing more ambient light to affect the exposure and show more separation between subject and background.

But be aware that the colour temperature of any artificial lights in the ambient light. Depending on how bright they may be, using slower shutter speeds can add unwanted colour that may pollute skin tones in your shot. The solution: Increase shutter speed but not too much. On the other hand, warmer light sources can add pleasant warmth to the photographs.

A faster exposure speed will generally result in a sharper image due to less movement during the exposure. It will also isolate the subject more from any back ground as less ambient light will be captured in the exposure.

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Comments (7) Trackbacks (0)

Christian
August 3rd, 2011 - 11:52

I’ve read that the duration of the flash is about 1/20.000th of a second.
Can this be true?
Shot by Scott
August 3rd, 2011 - 12:19

Depending on the manufacture it could be possible… and it depends on how they measure the timing of the flash.

Flash duration is measured in two different ways. These methods of describing flash duration define the time as the flash begins to glow and then dims at the end of the flash. The methods are referred to as t.5 and t.1…. t.5 describes the duration above 50% of the maximum brightness, and the t1 describes the duration of above 10%.

The t.5 duration is generally the method used by manufactures in specifications of their lights. This t.5 reference is not the best indicator of stop action capabilities of a flash. The t1 method gives us a better indication action stopping of a flash. T.1 durations are generally 3x the duration of a t.5. For example a monolight flash that is rated at 1/900 t.5 will have the action stopping of a 1/300, not really much action stopping.
Shot by Scott
August 3rd, 2011 - 12:24
julie
August 4th, 2011 - 10:02

Good article. I have experienced this a couple of times.
Christian
August 4th, 2011 - 10:08

Thanks for your explanation
Shot by Scott
August 4th, 2011 - 10:33

Also if you buy a flash base on its t.5 rating and only use your maximum sync speed you may also run into problems with banding due to its t.1 rating and the power out put. But that is a lot more complicated and a topic for another day.

The easiest answer is play it safe an use a sync speed lower then your x speed i.e. if you camera is rated at 1/200 then go down to 1/125 you you should be ok.
Vicco
August 13th, 2011 - 13:36

Good explanation, good stuff!

Yes, flash sync speed should be not faster than 1/200 or 1/250 plus RF transmitter delay (1/125 s is on the safe side). Unless … unless you use the whole flash duration for exposure In other words: there’s a trick how to use a long duration flash (flash on high power*) as some sort of continuos light source.

http://www.calvinhollywood-blog.de/2010/05/26/portyfotografie-mit-offener-blende
http://www.lichtkunst-stralsund.de/videos/357-video-highspeed-mit-studioblitz.html

=> For this trick, you’ll need really *long* flash durations and in addition a TTL speedlite in HSS mode to (optically) trigger the studio flashes …

Another trick, quite similar: With this speedlite /studio strobe combination, you can also trigger on the second curtain. I know of no other way to use 2nd curtain in the studio, do you?

All the best
Vicco

–
* The more powerful, the slower, … this is an almost proportional relation.
If you want to be fast for freezing action, turn down the power or use speedlites …. best is (fastest is) to use speedlites on really low power. If you need more light, use many of them.