I got a few questions about the Electronic View Finder on a mirrorless camera concerning flash photography. And yes, when you use the wrong settings it can be quite a challenge using a mirrorless camera in dark situations when flash is needed. The solution is fairly simple.
The optical view finder of a DSLR allows us to see through the lens, making the composition as we see fit. That image in the optical view finder is not influenced by any exposure setting and we have to rely on the exposure meter for the correct exposure. It also means we can see through the optical view finder perfectly when the exposure is completely wrong, or when we rely on flashlight in combination with the flash sync in a dark situation.
With mirrorless cameras the Electronic View Finder (EVF) is introduced. A real tiny digital screen that is refreshed in such a high rate it looks (almost) like it is an optical view finder. The beauty of that EVF is the ability to preview the exposure settings of our camera even before the picture is taken, thus having a visible control over how the image will look like when we push the exposure button. It is the similar image we see on the rear screen of the mirrorless camera, and it is also similar to the live view on a DSLR camera. This preview of the exposure setting is called exposure simulation, something that is turned on by default on mirrorless cameras.
For those who use flash photography a lot, it is common to use manual exposure for that. You set the exposure for the amount of ambient light you desire to be visible in the photo, and you use the flashlight for the exposure of the subject itself. When we don’t want the ambient light to register it is best to choose flash sync setting for the shutter time, which is often somewhere between 1/125 and 1/500 of a second. With this exposure setting the ambient light won’t show up and the flash light is the only light that will show up in the photo.
And there starts the problem with an EVF. When set to the default setting it will show exposure simulation and since the exposure setting is set on flash sync and not the ambient light, the EFV will show only a dark frame. You won’t be able to make the composition anymore, or sometimes even fail to use the auto focus.
The solution is very simple, but you have to change a setting in the menu. You need to turn off the exposure simulation of the EVF in order to be able to use it. After you have done this, you can use the EVF, or the rear LCD screen again, just like the next two images will show. This also is useful when you use live view on a DSLR for your flash photography.
Changing this setting requires to dive into the menu, or perhaps you can program this setting into a quick menu, or assign it to a custom button if possible. You can also program one of the three custom settings on the PSAM wheel, called [C1], [C2] and [C3] on a Canon, [U1], [U2] and [U3] on a Nikon, or simply , and  on Sony, with all the wanted settings for this kind of flash photography.
Every camera is different and acts accordingly. I noticed the ability of setting exposure simulation at [M] separately from the [P], [S] and [A] on a Hasselblad X1D-50c. On the Canon EOS R there is a measurement timer in the menu allowing the EVF to become brighter for a certain amount of time and making it possible for the AF to focus. You can use this setting to make a composition also but the frame will afterwards become dark again. On the Nikon Z7 the AF won’t focus at all, and I haven’t found a solution on that camera. I believe turning off the exposure simulation is the best practical solution.
If you blend in flash light with ambient light the view finder will stay usable with exposure simulation and this setting may not effect you at all. Unless you want to underexpose the ambient light of course. In that case the EVF will become darker proportionally. It it becomes too dark — which is funnily enough also influenced by the amount of ambient light — you might want to turn off exposure also.
So, when you use flash with a mirrorless camera, and the view finder is so dark you cannot use it, this setting may come to your rescue. Assign a button and you’re good.
Have you assigned a custom setting for flash exposure? Or do you have another EVF solution for using flash with flash sync on a mirrorless camera? Let me know below in the comments.