Dynamic range for dummies

[btaylor]

Hi all,


I work for a large mining company and our corporate photographer was on site recently to take a bunch of photos around our site. One of my good friends works in the community relations department and introduced me to him. Now even though he shoots Nikon (2 x D3s's... quite nice to be honest), he's a great guy and we got to talking and I even took him out to a couple of my favourite spots for some night shots over the mine.


To cut a long story short he briefly mentioned thatthe most important thing to look out for when looking to upgrade a body is the dynamic range of the sensor. Now I have a couple of other things that I also find highly important (high ISO performance, sensor size, AF performance etc etc etc). But I'd liketo know if these properties are in fact related to the dynamic rangeof the sensor. Anyway, I kindly agreed with him and we carried on shooting.


So I supposemy questions are:


What is dynamic range (in laymans terms) and how is it measured?


- My understanding is that it is the range within which you can still pick up detail in a shot. i.e without being a blown highlight or a completely black shadow. I realise that the measurement is the number of stops but how does this translate to real life.


What does dynamic range affect? Is it just colours/light? Is it related to ISO performance?


That might do for now but I'm sure as the thread progresses I'll have some more detailed questions. I really enjoy the technical side of digital photography so I'd love to get a better understanding of dynamic range. (sometimes though I think I need to remove my engineer's hat and donn a more creative one)


Thanks in advance, I look forward to your replies.


Ben

[crosbyharbison]

http://www.dpreview.com/learn/?/key=Dynamic_Range ("http://www.dpreview.com/learn/?/key=Dynamic_Range)





http://www.cambridgeincolour.com/tutorials/dynamic-range.htm ("http://www.cambridgeincolour.com/tutorials/dynamic-range.htm)

[Daniel Browning]

What is dynamic range (in laymans terms) and how is it measured?





You are in a maze of twisty definitions, all alike. You are likely to be eaten by a grue.


Seriously, everyone has their own pet definition of what dynamic range is. In the context of a processed photo (printed or viewed on the monitor), it generally means just what you wrote: the range between clipped highlights and black shadows. In the context of a camera performance metric, it can mean several things: the range generated by the camera's JPEG engine with default settings, and/or custom settings, or it may mean something about the raw files generated by the camera. If raw files, then the engineering definition of dynamic range is the range between clipping and a 1:1 signal to noise ratio (SNR) -- where noise is very strong in each pixel. But most photographers will never use that much dynamic range because the noise is too high for their taste, and it may have certain ugly characteristics as well, such as lines.



I realise that the measurement is the number of stops but how does this translate to real life.


Here's an example. At ISO 100 f/2.8, let's say the 5D2 raw file has good usable dynamic range of
around 9 stops. The variable pattern noise (temporal FPN) in the
shadows limits any more than that (depending on the color balance of
the light). A typical raw conversion will put white at 0.3 stops below
clipping, middle gray at 3 stops below clipping, and black at 7 stops
below clipping. So 6.6 out of 9 stops of dynamic range are used for the raw conversion.



At ISO 200+HTP f/4, the raw file, the dynamic range is shifted. The
scene luminance that was 0.3 stops below clipping in now 1.3 stops
below clipping, and one whole stop of clipped information is no longer
clipped. Similarly, scene tones that were 9 stops below clipping before
are now 10, and are lost to the pattern noise of the 5D2. Furthermore,
all the rest of the tones have increased noise compared to the above.
But the total dynamic range is still the same: 9 stops. If the HTP
instructions are followed, then instead of using 6.5 out of 9 stops, it
will use 7.5: white at 0.3 below clipping, gray at 4 stops below
clipping (instead of 3), and black at 8 stops below clipping.


Technically, both raw files have the same amount of dynamic range. They just fall over different parts of the scene. In the second case, the raw file used a different raw conversion to utilize more of that dynamic range in the image.






What does dynamic range affect? Is it just colours/light? Is it related to ISO performance?





Sorry, I'm not really sure how to answer these questions. [:D]






http://www.dpreview.com/learn/?/key=Dynamic_Range ("http://www.dpreview.com/learn/?/key=Dynamic_Range)


http://www.cambridgeincolour.com/tutorials/dynamic-range.htm ("http://www.cambridgeincolour.com/tutorials/dynamic-range.htm)





Good articles overall, but they're both flawed in that they claim that larger sensors have more dynamic range because they have larger pixels. In fact, they would have the exact same superiority in dynamic range even if they had pixels of the same size or smaller. But that's off topic for this thread anyway.

[btaylor]

You are in a maze of twisty definitions, all alike. You are likely to be eaten by a grue.





[:|]












...it generally means just what you wrote: the range between clipped highlights and black shadows.





Great, sometimes I like the uber technical side of things. For this one I'll take this lovely, simple definition and work with it.










Here's an example. At ISO 100 f/2.8, let's say the 5D2 raw file has good usable dynamic range of around 9 stops.





Does f-stop make a difference to the dynamic range of an image? If so would this be a reason to stop down when you don't need a thinner DOF?









Sorry, I'm not really sure how to answer these questions. /emoticons/emotion-2.gif










I'm not really sure what I'm asking so we'll leave it there. [Y]





Thanks for the replies.

[scalesusa]

In the days of film, film hadwhat we calledexposure latitude. That is to say that you could over expose or under expose filma reasonable amount and still get a excellent image. This was due to the high dynamic range of film.


Digital sensors have muchless dynamic range, so getting a good exposure is more critical. If you are shooting in bright sunlight, the dynamic range of the scene from the brightest to the shadow areas may exceed what the sensor can capture. Thus you have to choose overexposing the bright areas, or under exposing the dark areas, or both.


Graduated filters or polarizing filters may help to reduce the dynamic range of the scene.


One of the reasons photographers shoot in RAW format is that it has more dynamic range and will forgive overexposures quite a bit. Under exposures are not so pleasant, so always err to a slight overexposure if in doubt.


Some more info.


http://www.nature-photography-central.com/DynamicRange.html ("http://www.nature-photography-central.com/DynamicRange.html)