First & Second Flash Curtains: Bwha? And what the heck is Slow-Synchro?

Depending on what type of digital camera you have, you might have noticed in the Flash Menu, a choice between “First Curtain” and “Second Curtain”. Also, “slow synchro”. 

What the heck do those mean?

Well, okay. I had to read a bunch of articles to understand what was going on (and at least one article said the opposite of all the *other* articles, so there you go) with these flash settings.

The camera I currently work with is a Canon SX-20is. It’s a couple years old. Other camera brands such as Nikon don’t use the term “first” or “second” in their menus. Nikon uses “front” and “rear curtain synch” instead.

Here’s my camera so there’s a point of reference:

I love my Canon!  (image from canoncompact.com) Note the Flash button on the left side on the top of the camera body.

First Curtain flash is typically unlabeled as such in most point & cameras. It’s the default setting. But what IS it?

Every camera has a shutter. Digital cameras have sliding rectangular shutters (the curtains). First Curtain flash means that the flash goes off as the shutter opens, at the beginning of an exposure.  Depending on what setting you use on your camera, the background behind your subject will be dark, and your subject typically washed out if the flash strength hasn’t been adjusted.

So if First Curtain is the default, then what the heck is Second Curtain? I’m sure the pro photographers at The Lily Pad could probably add a whole bunch of information to this article. So pros, feel free to comment!

Second Curtain slides the shutter over the light sensor in your digital camera and times the flash to go off as the shutter is closing over the light sensor in your camera.  That is what happens inside the camera.  If you set your camera to Second Curtain, but leave the shutter open at 1/60th of a second (the standard or default setting for flash exposures), you won’t really notice much of a difference in your photograph from a First Curtain photo in terms of light blur.

Where the second curtain shines is when you use it for longer exposures or exposures using light as its subject. (like cars zipping past you leaving streaks of light) Also, Second Curtain is good to use with the Slow Synchro setting. Using these two settings in conjunction will give you photographs what will give you better lighting in the background, and a clear well-lit subject in the foreground.

Slow-Synchro lengthens the amount of time the shutter is open, allowing more light to hit the light sensor before the flash goes off. This has the effect of brightening the background. If you have a DSLR camera, you can “drag the shutter” by lengthening out the time the shutter is open while your aperture and ISO speed remain the same.

Now, if you have a point and shoot camera that doesn’t seem to have these settings, it actually might–only all the settings are programmed into a particular “scene” on your camera’s dial. Look up Night Snapshot, or a symbol of a person with a moon/star next to it. That is the setting that will generally have the second curtain, extended exposure time similar to the second photograph I took. Try it out!

With a DSLR and an external flash mounted onto the camera’s hot-shoe, your options are much more under your control. DSLR owners will be able to lengthen the exposure time as long as they want and get more effects.  Curious about what you can do with the second curtain?

Take a look at these sites: Digital Photography School, Neil Van Nekierk Dragging the Shutter, 13 Great Slow-Synch Images. Search for “second curtain” and “dragging the shutter” and much more will come up.

I hope this was informative and not confusing! Please ask questions in the comment section.

Julie (javamonster)