Find the appropriate ISO level
Now it’s time to think about the ISO setting. You will capture more of the tree’s branches if you use a higher ISO value, as the sky background will be lighter and the branches won’t disappear into darkness. Having tried ISO 200 and ISO 400, I chose ISO 800. If the flash is too overpowering, dial in some negative flash compensation, reduce the manual flash power, or just narrow the aperture (increase the f/ value).