5

I have a Canon Rebel T7i and Godox flashes. I am a real estate photographer, and I am using a multiple exposure method to expose the windows to see the view outside.

On especially bright days, I need to set my shutter speed much faster than 1/200 to get a good window exposure, sometimes closer to 1/500 or more. But when this happens it seems that my flashes, even though I have them set to full 1/1 power, are not putting out full power. But as soon as I go back to 1/200, they’re at full brightness again.

I have my camera set to HSS, but that doesn’t seem to help at all. Is it the flashes? Is there another setting I can try? If the curtain leaves the black band across the top/bottom of the photo that doesn’t matter to me because it’s only the windows in the picture that I really need. I'm usually set at ISO 200 f/8.

New contributor
Monica M is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
8

That's the nature of HSS. Instead of one full-power firing of the flash at a point when the entire sensor is exposed, it has to fire a series of very fast flashes at different points while different sections of the sensor are exposed between the slit caused by the first and second shutter blades. Otherwise, you'd get one band of well lit exposure through your image and the rest underexposed. There may be some high-end brands of flash that can do that high-speed series of flashes all at full power, but most can't.

  • None can. Not only because they must use the single charge of the capacitor to pop more than once, but also because full power flash pulses have the greatest difference between power at peak and power at cutoff. For the same flash they're also longer than lower power pulses. – Michael C 2 days ago
3

As noted in another answer, High Speed Sync has limitations on available power, because of the way the flash has to be operated to light the full frame. There are a couple ways to get around this.

Since you noted a dark band in the frame would be acceptable, because you really only need the window, one method would be to turn off the HSS. This will get you a band the width of the shutter slit, at the bottom of the image, that's correctly exposed by the flash -- whether that band is wide enough for your purposes is something you may have to determine by experience, but if you're only having to go up from 1/200 to 1/500, you ought to get something like 40% of the frame lit by the flash.

However, there's probably an easier way around this: with the camera on a tripod, take one frame with the flash off (giving correctly exposed outdoor view) and one with the flash on automatic or manually set to correctly expose the interior, then use HDR software to combine the two. This could also be done manually in any photo editor, just by cutting the bright parts of the window and pasting them into the interior image, or even by combining them on different layers and using a brightness mask to let the outdoor portion show through the indoor -- but an HDR processor is far easier to use and should give good results.

There's also an old-fashioned way to do this, that would have worked well with film: add more flash heads and stop down or use a Neutral Density filter to get an outdoor exposure below sync speed. This will also work for digital, so you don't have to shoot two frames with different settings and can see the final result on the camera display and be sure you got the shot you want before leaving the room. You may need to do some research on Guide Numbers to determine how many flash heads you'll need, but if you're only one or two stops over on the exterior, it won't exceed four.

2

Those are just flash basics. Flashes simply cannot put out full power in HSS mode, which HSS will then not likely be enough power this use for your real estate distances.

So for your use in this case, use camera S mode (Tv in Canon) so you can set shutter speed to 1/200 second so that HSS flash mode will not be enabled automatically. Limiting shutter speed to 1/200 will stop down aperture to a larger f/number, which will still be correct for daylight (called Equivalent Exposure). This higher f/number will also require more flash power (adjusted by TTL), but odds are speedlight mode probably has enough power, where HSS mode will not.

Your Answer

Monica M is a new contributor. Be nice, and check out our Code of Conduct.

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.