Exercise: Your Camera’s Dynamic Range
I had a so much difficulty with this exercise, to the point where I couldn’t achieve what was requested, and originally abandoned the exercise itself.
The dynamic range of any camera is the light range, from black to white, that the sensor can resolve without any pixel going beyond its resolution range.
As I fully understand what the term ‘dynamic range’ is when applied to any digital camera, I can only wonder why this has any effect on what I do as a photographer with my particular equipment. Whatever the dynamic range of my own camera is I cannot do anything about it, similarly whatever the dynamic range of any scene is that I choose to photograph I cannot do anything about that either. I certainly wouldn’t be worrying about how many f-stops of range I’ve got to play with when settling down to take any image. If the dynamic range is beyond that of my camera would knowing that stop me from making that image? I don’t think so; I’d still have a go no matter what. I’d look at the histogram, highlight and shadow clipping and make whatever adjustments I can, provided the image is still available to re-shoot.
So when you put the two together I have to make the best fist I can with whatever it is I’m presented and then make any possible adjustments within post-processing.
There is of course the possibility that I could use HDRI techniques to cover the entire range or image blending (I think that’s the correct term). If one end of the range is not as important as the other visually, one could always employ a filter or lighting to shift the dynamic range up or down dependent upon requirement.
Another way of finding out more accurately would be to take a Stouffer 21 step transmission step wedge, place it onto a backlit surface, probably a slide viewing light-box or similar, photograph the strip and then check the highest and lowest ranges without clipping or hidden by noise to determine the full range. Alternatively Imatest software could be used to help determine this range, but both of these methods seem a little extreme for a single camera sensor.
When it comes to post-processing, I found that this exercise provided me with some evidence that Photoshop 5.1 and Lightroom 4.2, both of which I use, do not in fact have exactly the same RAW conversion software as each other as I’d been led to believe. The same image RAW information displayed different highlight and shadow clipping when displayed in each product, leaving me to wonder which one was the true representation.
I took this question to the OCA Student Site Forum and posed the questions there, the link that follows will take you to that discussion. http://oca-student.com/node/94546
After thinking about this for some time, I decided to invest in the Stouffer step wedge. Taking advice from the American manufacturer I purchased the forty-one step version of the film strip rather than the twenty-one step as each step of the twenty-one is set to be an f/0.5 increment and only covers a maximum of 10.5 stops, the 41 step is set for f/0.33 increments and therefore covers 13.66 stops.
I took my slide viewer light-box and blacked out the screen with black cartridge paper with a slot of sufficient size to take the 9.5″ X 1″ strip without light showing around it. I then took a series of manually exposed images to get a best exposed set of results. The images below show that highlight clipping begins to occur at step 3 and lowlight (shadow) clipping takes place at step 33, this means that the dynamic range of my camera sensor is 10.
The most obvious learning point is that I now know what the dynamic range of my camera sensor is and accurately too. The next learning point is that by choice of shutter speed/aperture it’s possible to move the dynamic range up or down the scale, depending upon their settings, but the actual range of the sensor never changes, it just moves.