Posted by: In: In-Camera, Techniques 28 Jan 2011 0 comments Tags: , , ,

This is a follow up post to “What is HDR” and is the second in a trinity of posts about HDR. There are two phases to getting a decent image for HDR. Camera-side and Software-side. This post looks at the camera functions.

So – what do you need?

The answer to that, is that you need some form of manual control over your camera. You also need to know how to manually control your camera! Finally, you need a tripod, or a steady base for your camera (so that it doesn’t move)

As discussed in the last post, HDR is all about getting a balance between the lightest and darkest areas of your image. What I’m going to explain here, is how to take a range of images at different exposure settings so that you capture all the information. Beyond that (in the third post) I will detail how to blend these all together. But it’s important you know now that you’ll be blending these images in post-processing. That’s why the following is important:

– The camera must not move once you’ve started. The HDR software will cater for small movements in-camera, but you’ll be most likely shooting at low shutter speeds, and you need crisp, unshaky images to get the best results. Additionally, it’s probably wise to turn OFF auto focus and any image stabilisation. By reducing the light, the lens may want to hunt for focus giving you blurred images. When you’re set up with a tripod, find focus using auto-focus if you like, but then switch AF off.

– The Aperture must not change once you’ve started. Different apertures give different depths of field, so if you change the aperture through your shooting, some images will be out of focus beyond the focal point, and some will be sharp. When they are blended, it looks messy. That’s why Manual mode (M) or Shutter speed priority (Tv) if manual mode scares you, are the best options.

– The camera must be changed to shoot in RAW mode. JPEGS do work, but the effect and clarity is much better in RAW mode. There is simply more information in the RAW files for the post processing software to work with.

– The camera should be set to spot metering. You’re going to take light readings from different parts of the scene (the darkest and the brightest) and averaged meter readings will mess everything up. Set to spot metering and the middle 3% of the sensor is where the light will be measured.

So let’s walk through this with an example. My living room is a great place to start, as it has content in shade, and content in bright light. Just snapping a shot of the sofa shows the problem. When we expose for the sofa, the light coming through from the room beyond is totally white. We can’t see any detail.

Shows how a scene with multiple=

So what’s the solution?

Here’s where you need to know how to understand your camera. Looking at the display, when I point the camera at the sofa (the middle point of the viewfinder – spot metering meters this point), it shows a correct exposure at 1/10 sec, f5.6, ISO 500. However, when I point the camera at the bright areas, it shows 1/125 sec (f5.6, ISO 500 unchanged remember!)

Exposing for the highlights to get the top reading for HDR photography

So now we know that to capture all the detail in the image, we need to shoot exposures between 1/10sec and 1/125 sec.

Most modern DSLRs shoot in anywhere from 1/3 stop increments to 1 stop. I generally set my camera to shoot in 1/3 stop increments to get the best exposure possible.

So, in 1/3 stop increments, I need to shoot the images at: 1/10, 1/13, 1/15, 1/20, 1/25, 1/30, 1/40, 1/50, 1/60, 1/80, 1/100, 1/125.

“Twelve shots for a sofa?” I hear you cry. Yes. In the above instance, I wouldn’t take twelve, but then I don’t see a lot of artistic merit in a sofa… Outside, with a nice landscape, those twelve shots would merge into a lovely looking HDR.

In all seriousness, taking this number of shots isn’t a big deal. If you have shutter speed set to one of the wheels on the camera, it’s just a case of shoot, rotate wheel one click, shoot, rotate wheel, etc etc.

Misconceptions about HDR: i.e. “Why does my HDR look bad?”

“Five Exposures is best”

Some people will tell you that 3, 5 or 7 exposures are best for HDR, but that must be taken as a guide. If you want the best image possible, you need to take the number of photos equal to the number of stops (or fraction of stops) between the lightest and darkest area. In the above example, that’s 12 exposures. If we went in full stops rather than thirds, it would be 1/125, 1/60, 1/30, 1/15, 1/8 (five exposures)

“Auto-bracketing works fine”

Yep. It does. But the quality of the HDR can be a bit hit and miss. Auto-bracketing basically takes one shot at the correct exposure, then more shots +/- one or two stops. This is fine if you meter for the “middle ground” and there are no more than 4 stops difference between the brightest and darkest areas. If you’re in a hurry, by all means use this method – I did for years, but I’m now a convert to using a tripod and taking two light readings, then  a sequence of shots from light to dark.

“Hand holding works”

Also true, but you’re asking the software to marry up images that will have moved, and the end result is an image that has ghosting around the edges of your lines. Even the brightest day (equating to fast shutter speeds) will need slow shutter speeds for the dark areas. Again – by slowing down with a tripod, you get perfectly aligned images, as well as having to pause to consider other artistic elements that make up a good image. Composition being the most important!

For the tl;dr Crowd

  • Use a tripod, turn off Image Stabilisation.
  • Stop and think about composition.
  • Make sure you’re shooting in RAW
  • Once you’ve focussed, turn off Auto focus.
  • Make sure the camera is set to Spot meter and then meter the brightest and darkest areas.
  • Take shot #1 at one end of the shutter speed scale (1/125 in the above example)
  • Step through the range, taking one shot at each stop (or fraction of, depending on how you set up your camera). The more images you take, the better the HDR result will be!

Next time: How to blend the images in HDR software. You could make your sofa look like this!!

A final example of an HDR image

Yeah – it looks terrible, but as I said above, I wasn’t going to take 12 exposures of the sofa! In this case, I took just four exposures to “see what would happen”. For the software tutorial, we will use a proper image.

Next… Using Photomatix to create the HDR image