Final answer:
When correcting underexposure in photography, you typically start with a 2-fold change in exposure, but it may vary depending on the situation.
Step-by-step explanation:
When correcting an underexposure in photography, you will typically start by increasing the exposure by one stop or doubling the amount of light.
This is equivalent to a 2-fold change in exposure.
However, the specific fold change you need to make will depend on the level of underexposure and the desired result.
It is important to review the histogram and adjust the exposure accordingly.