After the AF modes and areas, we now talk about the external flash and how to use it for macros.
Firstly, check and set your flash sync speed and make sure you never exceed the shutter speed specified here. You will start getting black on the bottom of the frame if you exceed the sync speed.
Second, check the flash mode on the camera. If it is set to red-eye, then make sure you change it to normal. Most flashes support the red-eye double flash and that can totally ruin a wildlife shot.
Keep in mind that not all camera bodies have a popup flash.
Let’s now look at the modes a flash would offer. In general, you would have an auto or TTL mode which works exactly like a popup flash and you can control the flash via the camera. There are master and slave modes which allow controlling either a single or multiple flash setup. Finally, there is a manual mode and that is the only mode we are interested in here.
Since we use a flash cord to connect the flash and the camera body, we only need to set the flash to manual mode along with the zoom and power we want.
In the wild, one would generally not get a chance to fiddle with the power and zoom of the flash and we will see how to get around that. Recall the inverse square law for light falloff we discussed earlier? Yes, that is how we control the power of the flash in the wild. Simply changing the distance of the flash to the subject will increase or decrease the power of the light on the subject. We would, in general, never need to change the power once we are set for that depending on the GN of the flash and the capability of our camera sensor.
This is an aspect you will have to experiment and find out for your setup based on the aperture you use. I will discuss what I generally use in a later video.
Let us now look at the zoom and power aspects of the flash and how they impact our macro shots.
First, the zoom.
The zoom on the flash tries to match the zoom or focal length of the lens to cover the FoV for that focal length. A 50mm zoom would cover a wider area than a zoom of 90mm. In the TTL (auto) mode, the flash would automatically set the zoom to match the focal length of the lens on the camera.
So, where would we change the zoom to be more or less than the actual FoV of the focal length?
Recall the example in an earlier video where I used a zoom of 50 on the flash instead of the 90mm focal length of the lens? This was to spread the light out a bit more so we could see more of the surface and the reflections the objects created on the surface. The other case would be where you are lucky enough to get a subject in a clear area and want more of the natural background to blend in the frame rather than holding the flash on top of the subject for a dark background. In this case, you would point the flash directly at the subject, but, do not want intense light on the subject itself and therefore you can reduce the zoom to spread the light more than required for the FoV.
Now, let us look at the flash power.
Almost all flashes will shoot at the full power based on their GN, down to around 1/128 of the full power. Generally, the increments would be in 1/3rds but, can differ for different flash units.
In general, we will never use the full power mode for macros. A higher power for the flash implies a longer duration of the flash and vice-versa for low power. Understanding this part is critical for macros. Using a low power not only allows the flash to recharge faster (generally under a second), but, more importantly, since the duration of the flash is so short, it helps in freezing the subject and eliminating any shake we might get when shooting at 1:1 or higher magnifications.
For example, the flash duration range on my Godox flash is 1/300 – 1/20000 of a second. Imagine the speed of the low power flash. This is also the reason why the shutter speed cannot be used to cut the flash light and only the aperture can.
Therefore, my recommendation would be to use the lowest flash power that allows you to shoot around the base ISO of your camera to get the best possible details in your macro shots.
Now that we have covered the flash part, let us look at a few examples…
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