Portraits with 2-light setup results in blown out background

[gossamer]

I have a D500 with a 24-70mm, an SB700 plus a YONGNUO YN560 IV speedlight on a small tripod for fill lighting against a white backdrop, and trying to create a basic headshot. The YONGNUO flash is set as a slave to trigger on the SB700 flash. The SB700 is set to 1/2, although I've tried many different settings. The camera is set for f5.6 ISO 200 and a shutter from 320 to 1000.

I don't know how to describe the effect I'm seeing here where there's a point where it appears the fill flash doesn't fill the entire backdrop and instead stops at a certain point from the bottom:

The only way to avoid this is to set the flash to full power - 1/1, but then the background is completely blown out, of course.

I seem to recall this may have something to do with rear curtain sync?

Perhaps you have some general guidance on what I might be doing wrong? I'm not even sure what other information I can provide to help fix this problem.

 

[mrca]

I believe the max flash sync speed with a d500 is 1/250 and above that results in the shutter partially blocking the frame. Try lowering the shutter speed to 1/250 or 1/200. I don't know if your yongno flash is capable of high speed sync. It could be that the sb700 on the subject is but the background light is not. Do you have the sb700 set to hss? Why? Why the high shutter speed inside? Are you trying to kill ambient? Power setting alone tells us nothing as distance and any diffusion effects the exposure.

 

[greybeard]

I'm pretty sure the yongnuo won't high speed sync and is just dumping full. Like others have posted, slow your shutter speed to 1/200 and see if that helps.

 

[cgw]

With respect, you might learn a great deal from this site:

Strobist

strobist.blogspot.com

 

[garygruber]

First off, Your flashes are too close to the camera and your subject is too close to the background. Try using umbrellas to avoid the harshness of the flash. I use a tent made from white parachute material, and this was done with a single light shot through the tent (you can see the position of the light by looking for the catchlight in the eye):