How to shoot rear curtain with OMD E-M5 and Inon Z-240?

When I use the rear curtain (2^nd curtain), I get a flash at both the beginning and end of the exposure, with the one at the beginning brighter. I find that odd because I thought the flash should be at the end of the exposure.

Now when using rear curtain with external strobes (Inon Z-240 type 3, optical) the strobes fire fire at the beginning of the exposure. So it's not working the way I hoped.

Can this be done? Are some of my setting wrong or am I expecting too much?

Thanks for your help!

Is the camera set in A or P mode? Rear curtain sync does not always fire in P or A modes. Also, what is your shutter speed when this is occuring?

I have tested it with M, S, A and P modes with different shutter speeds between 1 sec and 1/15. Always the same result, two flashes both the beginning and end of the exposure.

I have tested it with M, S, A and P modes with different shutter speeds between 1 sec and 1/15. Always the same result, two flashes both the beginning and end of the exposure.

I believe that this camera needs a pre-flash to determine flash exposure. Many cameras fire a pre-flash to meter, then open the shutter and fire the flash that exposes the scene. During normal first-curtain operation, you probably don't even realize that it is firing twice (once for the pre-flash, then again for the main flash). However, when you shoot second curtain, the time between the pre flash (before the shutter is open) and main flash (at the end of the exposure) is more pronounced so you notice it easily. The pre-flash should not be seen in the actual photo.

Mike