How to reduce overexposure with speedlight?

[MLeeK]

If you are close to the subject with the background in the distance you should still get a fairly shallow DOF using a bit smaller aperture. Otherwise a ND or a couple of them will definitely make a great difference.

 

[KmH]

A ND filter blocks the strobed light too, so little if anything is really gained by using one.

That's right, I forgot every flash ever made only fires at a single non-adjustable power level...

There is an upper limit to the amount of flash power the unit can produce to over power the sunlight.

 

[Rephargotohp]

A ND filter blocks the strobed light too, so little if anything is really gained by using one.

That's right, I forgot every flash ever made only fires at a single non-adjustable power level...

There is an upper limit to the amount of flash power the unit can produce to over power the sunlight.

The ratio of flash power to ambient remains constant before or after you put the ND on. But it ALL is reduced by 4 stops necessitating you open the aperture by 4 Stops (If it was a 4 stop ND)

You didn't all of a sudden reduce flash power by placing an ND filter on the flash. It's on the lens

If you could equal ambient before you can equal ambient after, You just need to open your aperture up..thus shallower DOF

 

[Rephargotohp]

There are some downsides to using a ND though, The reduced light through the lens can affect AF, Plus it reduces the light in the viewfinder making it difficult to see in contrasty situations- Think split lit alley
Another option is to NOT shoot with a shallow DOF, Instead put your subject in a beautiful background and celebrate it rather than try to diminish it. We use DOF to isolate and highlight our subject, But you can also use OCF to accomplish that too by providing good light on the subject which will isolate it from a background, in a different way than DOF, but in a good way..if done right

 

[fokker]

For simplicity, you could also try using a reflector if you're shooting into the sun.