I am a beginner in photography. I take portraits indoors. How much does it cost to fill the light with an auxiliary flash (reflective umbrella)?

If only the flash is used indoors without natural light, the shutter will be set to1125 seconds. If there is natural light, it will be set at the aperture first. But it should be noted that if there is no high-speed synchronization of the flash, the shutter should not exceed the maximum synchronization speed. If there is high-speed synchronization, don't worry. As for the aperture, it depends on what effect you need. Generally, if you take portraits, you mainly blur the background with a large aperture, but if you take wide-angle environmental portraits, you may also need to use a small aperture. However, it should be noted that it is best not to use the maximum aperture of the lens when using a large aperture, because generally speaking, the imaging of the maximum aperture is often not very good, and it is best to lower one or two steps.