S1 and S2 modes on a flash: what's the difference?

Flash photography can be quite daunting, but once learned it can give your photography an edge and yield amazing professional looking results. Shoot in TTL, S1 and S2 modes or using a shutter release button, once the basics of flash photography are understood it can be very simple to really make a dramatic change in your photography. It's one of the biggest improvements you can make and offers a level of versatility for difficult low-light situations.

So what are S1 and S2 modes? These modes are simply Optical Slave modes, hence the letter S. Still not sure? So read on.

There is a lot to learn about flash photography. This article is not intended to describe how to get started with flash photography or most of the basics of flash photography. There are many articles already published on photography flash on Enhance Photography. You can try the

Crash course in flash photography

to get you started on this. Or if it's too basic, you can try

Jim Harmer's lighting in a flash

video workshop that takes flash photography to the next level. This article is specifically aimed at explaining the optical slave flash modes called S1 and S2 and will not go into detail on other topics related to flash photography.

There are many ways to use a flash. You can stick it in the camera's hot shoe and fire it in TTL mode (stands for Through the Lens, if that doesn't make sense I recommend one of tutorials mentioned above). You can bounce the flash just by pointing it at ceilings, walls and other surfaces and away you go. You can also use the flash in manual mode in this form where you have a much more creative control over the flash, similar to shooting in manual mode with your camera. In this mode, you can change the flash output, among other settings, to light the scene as needed. All of these modes are triggered by a direct signal from the camera, through the hot shoe and to the flash.You can use a light stand to remove your flash from the camera for much more controlled light and directional. The flash can a can then be triggered either by a radio transmitter or using an optical slave mode.

The benefits of Off Camera Flash (or OCF as it's abbreviated) are well documented and I don't intend to cover them here, but it's safe to say that if you haven't tried it, you definitely should , experimenting with OCF was one of my most enjoyable photography experiences and I still love it today. So I definitely encourage you to use slave modes, as it's an easy way to get started. Slave modes work by triggering the flash when the flash sensor sees light from another source, whether it's a a studio flash or strobe. This is useful for triggering multiple flashes around your image from the flash of a single unit. The triggering flash can come from any source, such as your pop-up flash. up, a camera-mounted flash, or an OCF activated by a remote shutter release. Any of these methods will activate the flash in optical slave mode.

S1 and S2 modes can be used to easily and quickly set up and trigger multiple flashes in a large area

Where the S1 and S2 modes differ is when the flash is set

in optical slave mode will be triggered.

It may be different for different models of

This may be different for the different flash models you have so you will have to read the manual for yours but here I am trying to relay the principle of these slave modes.

Remember TTL (mentioned briefly in this article)? When TTL is on, many flashes send out an almost invisible first flash to get the metering signal to allow the TTL to work, then a second flash illuminates the scene for the actual exposure. This ensures that the camera and flash get enough data and information from the scene to be able to calculate the correct exposure.

In many cases (again check the manual for your specific flash), S1 mode will fire the slave flash as soon as it sees that initial flash. This result is similar to what you would get with a radio-slave flash. To use In this mode, the master flash should be set to manual flash and TTL should not be used in this case.

S2 is programmed to ignore this pre-flash required for TTL and run on the second flash, which is the actual flash that will light the scene from the main flash. So if you want to use the flash's TTL functionality, your slave mode preferred is probably S2.

Optical slave modes are great if you have a source flash to trigger them. As mentioned these would work with pop-up flash, camera flash or OCF. With OCF you would need a trigger to activate the flash of the main flash which would then trigger the flashes in S1 or S2 modes.

The disadvantages of using slave modes are that the flash power of slave flashes cannot be controlled remotely. This means that you have to physically change the flash settings on each flash individually. This can get a bit cumbersome when you have set up a flash at a wedding reception with a flash in every corner of a large room. This also means that the lighting conditions cannot be changed quickly and makes it difficult to use the OCF in these situations and that a remote shutter with the ability to change flash settings is more appropriate. These modes are also unreliable outdoors in bright ambient light conditions, if the flash is changed, preventing the slave flash to see the light pop from the master.

Slave modes work great with simple setups and shots where conditions are more controlled. In the studio or at home for a family shoot would be ideal.

Slave modes are a great way to access OCF and an easy way to add additional flashes into a scene. The main benefit is its simplicity to fire up another flash and just fire. It has its downsides, but it certainly has its place in flash photography and can be a very useful feature.

So go ahead! Try out S1 and S2 modes and join the discussion on Improving Photography and let us know how it worked for you!