1. Understanding High Dynamic Range (HDR) Photography
When
we refer to Dynamic Range we talk about the difference between extremes. As it
relates to photography and exposure we talk about the difference between the
lightest part of the scene and the darkest parts.
Dynamic Range is expressed as a Ratio. So in that context, the human eye can see in a range of approximately 10,000:1. In comparison, a good digital camera can capture a scene with about 1,000:1. So, we can see that the eye is much more capable of viewing a range of brightness than a digital camera. Even more incredible is that a scene with both dark and light aspects–light as dim as room lighting, and Sun lighting in a window–can scale as high as a Dynamic Range of 100,000:1!
So, in conventional photography, we have to make compromises. We can expose for the highlights and get them without blowout, but the shadows will be dark and full of noise. Or, we could go the other way and expose for the shadows, but then we would blow out the highlights and lose all detail.
We could use a split Neutral Density filter, and half of the image would be one exposure and the other half would be 2 or 3 stops less depending on the filter. But that would only work with the straight line of a horizon. What if you were shooting an odd-shaped mountain or an open doorway? There is no way to put these shots in a standard photographic filter.
But if we were to make an image that exposed for every area “just right” we could expand the dynamic range of our camera to make it comparable to what our eyes can see and beyond. That is what High Dynamic Range Photography is all about.
Before we begin, let me make one thing clear that people often get confused about. We are going to use High Dynamic Range Photography but our end result is going to be a Low Dynamic Range image (and all current HDR images are really Low Dynamic Range images). As things stand now, no printer or computer display is capable of displaying a truly High Dynamic Range image.
Dynamic Range is expressed as a Ratio. So in that context, the human eye can see in a range of approximately 10,000:1. In comparison, a good digital camera can capture a scene with about 1,000:1. So, we can see that the eye is much more capable of viewing a range of brightness than a digital camera. Even more incredible is that a scene with both dark and light aspects–light as dim as room lighting, and Sun lighting in a window–can scale as high as a Dynamic Range of 100,000:1!
So, in conventional photography, we have to make compromises. We can expose for the highlights and get them without blowout, but the shadows will be dark and full of noise. Or, we could go the other way and expose for the shadows, but then we would blow out the highlights and lose all detail.
We could use a split Neutral Density filter, and half of the image would be one exposure and the other half would be 2 or 3 stops less depending on the filter. But that would only work with the straight line of a horizon. What if you were shooting an odd-shaped mountain or an open doorway? There is no way to put these shots in a standard photographic filter.
But if we were to make an image that exposed for every area “just right” we could expand the dynamic range of our camera to make it comparable to what our eyes can see and beyond. That is what High Dynamic Range Photography is all about.
Before we begin, let me make one thing clear that people often get confused about. We are going to use High Dynamic Range Photography but our end result is going to be a Low Dynamic Range image (and all current HDR images are really Low Dynamic Range images). As things stand now, no printer or computer display is capable of displaying a truly High Dynamic Range image.
2. How do I shoot a HDR Photograph?
A High Dynamic Range Image is composed of 3 to 7 of the same image at different exposures. Each image is at perfect exposure for every level of brightness in a scene. How we adjust the exposures is critical. If we kept the shutter speed constant and adjusted the aperture, this would give us varying Depths of Field–an unwanted characteristic. We want all the shots to look the same, only varying in exposure. We could vary the ISO, but higher ISOs add more noise and we want as noise-free an image as possible. Since HDR is an additive process any noise will be multiplied. So that leaves us with one choice: Shutter Speed.
To begin setting up your HDR photo shoot, set your camera on a sturdy tripod. This will ensure each image in the sequence is exactly the same. Set your ISO for the lowest noise and set your aperture for f16.
Yes, you could use wider apertures, but in my images I want detail, since capturing extreme detail is the reason we take HDR images. We want that detail to go as far into the field as possible, so that is why “I” suggest f16. YOU, don’t have to. This is one of the many artistic choices you can make when it comes to HDR.
As far as varying the Shutter Speed, we have two choices. We can set our camera to AV mode and use theAuto Bracketing feature most cameras have. Most Canons are limited to 3 exposures at the interval we choose (+ – 2EV Max). Certain Nikon models allow for greater numbers of auto shots and a wider spread of EVs (Exposure Values).
I recommend a wholly manual approach. I find it allows for a faster process, as I don’t have to go through any menus to set it up and will have more options at my disposal if I want to make a last minute change to how many exposures I will shoot, and at what intervals. But that choice is up to you.
3. What type of images do you use for HDR?
A HDR image is a 32-Bit image. This means that the image is capable of an infinite number of different tones and brightness levels. We need to produce the best images possible that will leave us with as much information as is possible. Since no camera shoots with 32-bits we must make do with the options available to us. This means shooting RAW or Tiff images, as these formats are both capable of 16-Bit which, while not infinite, gives us about 64,000 different levels of information.Can we use JPEGs? You can, but since JPEGs are only 8-Bit they are only capable of 255 different levels of information. While they are not optimum at all, they can be used in a pinch..
4. How many exposures will I need and how far apart should they be?
In most cases 3 exposures are all that is necessary and 2 stops or 2 EV apart is sufficient. If you have the sun in the shot or bright sunlight you should use more. I like to shoot at least 5 shots and have them only 1 stop apart but I am going for a more realistic look, which may or may not be what you want from your image.
Now that we have our equipment set up correctly we are going to take our 3 shots. The first one will be with your meter centered for a good average metered shot. For your second shot, we will dial back the shutter speed until the meter reads -2, then we will take our next shot with a meter reading of +2. If you use the Auto Bracketing feature of your camera, this will be done automatically for you.
In my own shoots, I start at 0 Meter and that is my first shot, then I do one at -1, -2 and then (if I have sun in the image) I also bang one hard at -4 because I want to make sure that I have no blow-out in the brightest part of the image. Unfortunately, there is no meter reading for -4 so I need to figure out what that would be. The good thing is that since we are using Shutter Speed it is quite easy to figure out, as opposed to aperture which is Logarithmic. If my -2 exposure was 1/50, I multiply x2 (1 stop) and then again x2 (1 more stop) and I get 1/200th of a second and I set my exposure at that. After that I take one shot at +1 and one at +2. Rarely will you have to go beyond that on the + side, since +2 normally exposes shadows quite well.
Below are some examples of a Shoot Pattern. The first shot is what your shot would look like if you did not use HDR photography.
