There is a challenge to shoot HDR of a subject in a studio, but the problem is that the subject is illuminated with flashes that flash momentarily in complete darkness. Because of this, it is not possible to change the exposure on the camera. Therefore, it was decided to change the flash power between shots for HDR. But we faced the problem that the software for creating HDR from a series of images requires information about the exposure of the camera. In our case, we only changed the flash power, and the camera settings remain unchanged. Therefore, it is not possible to calculate HDR.

As a result, the question arises, is it possible to calculate HDR in some software without information about the exposure of the images? Or does it all make no sense, and is this information required? And if necessary, then there are suggestions on how you can shoot HDR in such conditions?

  • This makes no sense to me. What software are you using to create HDR from the bracketed images? As long as the file names are different, the software shouldn't care what the EXIF info says the Tv, Av, and ISO were for each shot.
    – Michael C
    Feb 25 '21 at 12:16
  • @MichaelC I am using Photoshop HDR Pro. Due to the fact that I only changed the flash rates between photos, Photoshop says that the exposure is the same in each shot and therefore the result is incorrect Feb 26 '21 at 6:14
  • Then I would suggest using a better HDR software that lets you load whatever images you desire... But why do you need to do HDR with a flash? The whole point of flash is to expose everything at the same relative brightness, so that nothing is too dark or too bright to fit in the camera's dynamic range for a single shot.
    – Michael C
    Feb 26 '21 at 15:15

Software like Photomatix will let you specify the exposure offsets for the images. If trying to use Adobe, then you will need to modify the exif with an external editor.

Alternatively, shutter speed does not affect the flash exposure and will allow you to bracket using flash power and cause an exif difference.

But your premise is wrong from what I can see... the subject being illuminated solely by flash does not prevent bracketing the exposure with camera settings. ISO affects the flash exposure, so you could bracket using ISO instead; and w/o significant penalty with many cameras as long as you don't go too far with it. Or you could bracket with the aperture setting which also affects the flash exposure... but that will affect the DoF which might be undesirable.

What strikes me as odd is the need to do HDR in the first place. HDR is really only useful when the dynamic range of the scene/lighting exceeds the camera's capability; but you are creating the lighting and dynamic range... it's within your control.

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  • Thank you very much for the answer! We will try your advice shortly. We need to shoot HDR in studio lighting with flashlights to create an HDRI. Feb 26 '21 at 6:22

A solution is to alter the EXIF data of the photos to make the HDR software believe that the exposure is different.

Normally, a factor of two on the power (halved or doubled) should entail difference of one EV (in the EXIF, better translated as a change is exposure duration, since this doesn't change the DoF in case it matters).

The problem is figuring out how accurate are the flash settings.

Otherwise, on the camera you can sill change the aperture, and if you don't want to change the aperture you can change the ISO.

  • But does the flash power somehow correlate with the exposure of the pictures? HDR needs exposure, but how do you get it from flash power? Feb 25 '21 at 9:26
  • A factor of two on flash power should be one EV.
    – xenoid
    Feb 25 '21 at 11:20
  • @xenoid That depends on the model of the flash. Some studio monolights have flash powers expressed as 1-2-3-4-5, etc. where full power is the highest number (n), 1/2 power is n-1, 1/4 power is n-2, and so on.
    – Michael C
    Feb 25 '21 at 12:20
  • If the room is totally dark except for the flash, why not change Tv? As long as you stay under x-sync, your results won't be affected by the specific Tv, but whatever insane software needs to compare exposure between shots would be happy. You'd have three Tv values of, say 1/200, 1/100, and 1/50. Since you're bracketing shots, the camera is already on a stable tripod.
    – Michael C
    Feb 25 '21 at 12:23
  • @MichaelC Good remark :)
    – xenoid
    Feb 25 '21 at 12:52

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