Exposure vs. Levels: Differences in Practical Use

Question

I would like to better understand the differences between the Exposure control in the Exposure Adjustment section and the White, Gray and Black Levels sliders in the Levels Adjustment section. For example, I am working on a Raw-format image that is somewhat over-exposed. The Exposure control allows me to force it down by about 6/10 of stop, which seems to do a nice job of adjusting overall exposure, and the results are obvious on the histogram. What I'm not clear on is whether I can achieve the same effect using only the Levels adjustments. I know how to set white and black points in Levels, and understand that the gray level adjusts overall brightness, but is there a way to control exposure with levels or are they two different facets of raw adjustment?

Answer 1

They are two different aspects.
In general, raising the exposure by a stop raises the values of all pixels by the same amount -- say one stop.
If you are familiar with the zone system, then using exposure to change something that is neutral grey (zone 5) and making it white with detail (zone 7), should also pull things that are black (zone 3) to neutral grey (zone 7).
Using levels should not do this -- it is effectively setting black and white points, and it ends up increasing contrast at the same time (because, you could take a low contrast shot, where the histogram was very compressed, and use levels to ensure the photo has a true black point and true white point, thus increasing the dynamic range of the shot).
This is a fairly vague description -- but the way levels and exposure tools work is fairly well detailed, though you'll find a larger breadth of documentation that uses Photoshop as the medium.