This Professional DF-400 Speedlite Camera Flash for Nikon D3000 D3100 D3200 D3300 D5000 D5100 D5200 D5300 D40 D40X D50 D60 D70 D70X D80 D90 D7000 D7100 D300 D300S D600 D610 D700 D800 D800E Canon Rebel SL1 T3 XSi T1i XS T2i T3i T4i T5i EOS 40D 50D 60D 70D 7D 5D 5D Mark II 5D Mark III and Pentax Samsung Olympus Panasonic Ricoh DSLR Cameras and Digital Cameras with Single-Contact Hot Shoe features 3 flash mode. M mode, In this mode, you can adjust flash brightness according to your own preference, the speedlight will flash under the camera synchronous signal. S1 mode, In this mode, DF-400 will trigger flash with the main speedlight first flash, the effect is the same as using radio trigger. When using this mode, your main speedlight should be set to manual flash mode, using neither TTL flash system nor red-eye removal function which caused multiple flash. S2 mode, S2 mode is similar to S1 mode and is also known as "preflashing cancel mode", but it can ignore the preflashing from TTL, so you can use it to support the main speedlight that working in TTL mode. In particular, if S1 mode is unable to synchronously flash with your built-in speedlight, you can try to use S2 mode.