Learn about exposure range and how to use it to get the brightness in images correct.
Getting Into Exposure Range
The reality is that our sensibility about what images look good comes from our own sense of perception. Our eyes and interpretative brain can handle a whole range of contrasts and light paradigms without many problems. These images may look good to us because we have the ability to handle the diversity in the frame, but often times film and video technology cannot handle this in the same way. The ability for a digital video or motion film camera to capture both extremely dark and bright areas in the same frame is referred to as its exposure range.
Estimating Exposure Range
Exposure range will become less of an issue as digital video and high definition technology matures, though video technology traditionally has a much smaller exposure range than film does. It is a persistent issue when it comes to actual motion film stock. You want to be able to pick film stock that will pick up the images you are looking for, but you also want versatility so you can adapt to situations and new ideas.
What you want to find is a film stock that has a large exposure range. This can sometimes be referred to as film stock with a sizable latitude. The over all latitude ties in directly to how long the strait area of the film stock's characteristic curve is. When looking at film stock types you can also estimate the over all exposure range often by the type of film stock it is. For example, reversal film stocks usually have a range of about five stops.
The way you estimate how to respond to exposure range is by using a light meter and measuring f-stops. The f-stop reading on two different areas can give you your estimated range of the image. You can then compare this to your video equipment to see if it can handle it. For example, if the range between two areas in the same frame are around eight stops then you will have trouble with most reversal film stocks. This can help you decide whether or not you need different video equipment or if you are going to have to add light to a scene artificially.
Make sure you always employ this calculation and know what your exposure range is before you enter into live production.