Courthouse Towers at Sunrise - Arches National Park, Utah
Link To Original Image: http://www.tom-hill.biz/Galleries/Scenics/Utah/20957775_CZGg5B#!i=1726113116&k=stmCTvZ
If you're new to digital photography you might already know there are a million compromises to deal with when out in the field. It all has to do with the limitations of your equipment meaning your camera does not see what you eye sees, which might be a surprise to you. Today's topic is about one of those limitations. We're going to talk about dynamic range.
Dynamic range is the breadth of luminance from very dark to white bright. This breadth is usually measured with a thing called Exposure Value (EV) or if you're old school, in F-Stops. Essentially the increase in brightness--i.e. luminance--on a dark gray object to one that's "twice as bright" increases it's EV by one or a single F-Stop. For two EV's it's a double double or 4 times the light increase.
According to Wikipedia the human eye with it's brain involved and various other chemical reactions can discern about 20 stops or about a million times the light increase. I've heard the number about 11 stops, which seems to make more sense. Still it's a huge number. If you're wondering, your camera probably does about 5 stops meaning whatever your camera sees is not nearly what your eye can do. So begins the quest to get more than your equipment will allow.
The technique we're talking about today is HDR. I have an article about what HDR means:
The basic premise of HDR is collecting two or more exposure values of the same scene then merging them together using software back at home. In the example I'm using today, I collected two sets of exposures separated by two stops--or four times the light.
The technique I'm teaching here uses Photoshop and it's layers and mask features. If you're familiar with these you can easily understand what I'm about to introduce.
The idea is you stack one exposure on top of the other then use a mask to mask out portions of the upper layer to reveal the lower one. The technique I'm teaching here is you'll be stacking layers with the bottom most the darkest layer with the upper one a bit lighter. In this case, the dark layer has the best highlights. The upper layer has the best shadows. The goal is to build a mask that allows the best highlights--the sunrise--to come through while preserving the best shadows.