What is ‘dynamic range’ and how does it affect our photographs?
I think one of the most difficult issues most people face when taking photographs is how to record a scene as we see it with our eyes. Quite often the scene we are trying to photograph has an extreme range of brightness from very dark areas to very brightly lit. Our eyes are remarkable as they enable us to see a very broad range of light. However, often it can be quite frustrating that our camera cannot record all of this range in one photograph.
This is the dynamic range – the difference between the darkest and brightest areas. It is measured in Exposure Value (‘EV’) or ‘stops of light’.
Our camera’s sensors have a limit on their ability to record extreme values and as such you will sometime find that it is not possible to achieve a single shot that records all of this information correctly – the camera simply cannot capture the full range of brightness and tones either leading to the dark shadow areas being too dark or the brighter areas becoming overexposed. Some scenes just have too wide a dynamic range from dark shadows to bright highlights. This is often the case inside buildings looking out of the windows at the daylight, or at dusk or sunset.
In this multi-part tutorial, I am going to explain what preliminary steps you should take when faced with such a situation and any tips and tricks to help. The next tutorial will explain how to take bracketed photographs and the final tutorial will provide a visual guide how to blend the exposures to provide a more accurate representation of the scene from the brightest elements to the darkest shadows.
When will you know you have exceeded the dynamic range of your camera?
This is usually pretty simple to see once you have taken a photograph. You can see when reviewing your image that the darkest areas of the image will be black and underexposed and/or the highlights or brighter areas are completely blown out and are just white.
Alternatively you can check your histogram and see whether your camera has been able to record any data for the shadows or highlights. To recall, under-exposed elements in your images will show the histogram clipping on the left side and overexposed highlights clipping on the right side. Please click here to read my earlier article on the histogram and how to read it.
Just to re-repeat, sometimes it is extremely difficult to get and accurate reading of an image from the screen on the back of the camera. This could be because you are out in bright sunlight or have the brightness settings on your screen set very high. As such it may be too difficult to know if you have completely under or over exposed an area of your image. This is where checking the histogram is a great help as you will be able to see from a glance if you have done this. Alternatively a great feature on many cameras and one I use myself is to turn on the highlight warnings that flash white areas in the playback image where you have over-exposed.
Quite often where you have over or underexposed an area of your image, you can re-shoot your image with amending the appropriate settings (such as exposure compensation, aperture or shutter speed). However, this will only fix one of the ends of the dynamic range applied to the whole image. Where you have a histogram that is showing very wide range of brightness, shifting exposure to fix one will affect the other extreme.
How to deal with the extremes and fix the issue?
- Whilst flash may help lighten some shadows, it is often unlikely to be much use to solve this issue. It may make the brighter areas overexposed or it may not be possible to uses a flash effectively due to distance of the subject (a flash won’t light up a mountain or other distant element in a frame).
- Neutral Density Filters (ND Grads) can help to darken elements of an image but again can only work in select situations. These are often used where the sky is the only part of the image that needs to be underexposed. I will write a tutorial about ND Filters in the coming weeks.
- Shooting in RAW format will provide you with additional leeway in terms of EV and dynamic range. In post production, you will be able to recover highlights and shadow areas of your photographs much more than with a jpg file, without damaging the data recorded. However, RAW data will only realistically give you an additional 1 EV of data and this may often not be enough to solve the problems you have.
- The only other way to deal with this situation is to take multiple exposures, known as bracketed shots covering a wide range of exposure values. This is know as High Dynamic Range photography (HDR) and I will explain this in further detail in the next tutorial.
I hope this tutorial helps to explain the dynamic range problems that most photographers experience.
Once again please feel free to contact me if you have any questions or comments about this post (or anything else on my website), and to pass this tutorial onto any photographer friends you think may benefit from it.
Until next time!
Leave a Reply