Exposure Science

Landscape Photography Workshops Lesson 04

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Lofoten, Norway. Fine Art Landscape Photography Workshops by David Osborn Photography

Exposure Science

Lofoten, Norway by David Osborn.

The Camera Response Curve

28. What Is The Camera Response Curve?

The camera response curve is a graph showing the relationship between the amount of incoming light received by the camera and the tonal value of that light recorded by the camera. The red line, my own Nikon D800E camera response curve created from fifty exposures then plotted in graph form. The green line represents the linear curve if the camera recorded identical tones as the subject. All cameras have almost identical camera response curves.

29. What The Response Curve Tells Us

Cameras change the tones we see. Graphing the camera response curve allows us to quantify those changes. If the camera did capture the tones we see, then the red line would overlay the green. The ‘changes’ being the difference between the two lines. The angle of the red line indicates the level of contrast. Steeper the angle, higher the contrast, greater the tonal separation. Flatter the curve, lower the contrast, more compressed the tonal separation.

30. What Does This Mean For You?

Highlight tones above 50%, A ~ B, gain 45% more contrast giving enhanced tonal separation, great for flat skies. But the shadows are killed. Below 50%, B ~ C, there is a 53% reduction in contrast and tonal separation. The darker the shadow tone, the worse it becomes – 50% ~ 75% shadows lose 26% contrast but from 75% ~ 100% a whopping 79% reduction in contrast and separation! We cannot create rich shadows with these numbers, we must overexpose the shadows.

Camera Response Curve
Overexposure Explained

The Key To Rich Shadow Tones

31. Camera Data Versus Computer Generated Data

Interpolated data is artificial computer data. The computer sees Tone #1 and Tone #3 then creates Tone #2 to fill the gap to make continuous tone. It is created when we stretch the tones in software by brightening the shadows. Problem is Tone #2 is crude, solid tone, containing no subtones. If captured by the camera, it would contain subtones. Camera tones are always richer because you cannot create in software what you did not capture with the camera.

32. Expose For The Highlights Then For The Shadows

Basing the exposure on the highlights, the shadows will be terrible; compressed, having no separation. Brighten those shadows in software, the tones are stretched introducing interpolation. The ideal solution is overexposing the shadows, moving them up the red line away from the flat part of the curve into the straight-line area. This way the tones will gain natural contrast and separation ‘in-camera’. The result is rich shadows full of detail, contrast, and subtle tones.

33. Then Build The Picture With Camera Data Only

If we manipulate data, we degrade the quality of the data. The goal is to create the initial photograph without needing any manipulated data. The highest quality data is pure camera data – so we try to create the initial photograph using pure camera data only. We divide the exposure into two problems: highlights and shadows blending them together in Photoshop later. Highlights will contain good separation, the shadows we overexpose to get good separation.

Overexposure Explained

The Camera Histogram

34. The Histogram Falls Over ~ Then Pulls Away

How do we know we have the best exposure for our shadows? Watch the camera histogram. As we overexpose each frame the camera histogram moves to the right. More importantly, it will change shape. The vertical line pivots at the corner and falls over. It continues to change shape, then pulls away, creating a gap on the left. When the histogram no longer changes shape and has a good gap, you have the maximum exposure. Do not worry about the highlights.

35. The Aircraft ‘Smooth Take-Off’ Analogy

Smooth camera histogram, smooth tone. Brutal camera histogram, brutal tone. Imagine the histogram was a graph of your take off as a passenger in an aircraft. If the histogram is vertical on the left, it’s a vertical lift off – a rough take off! However, if the histogram is like a smooth ramp – a smooth take off! The same with tone, the smoother the histogram the smoother the tone. It also means you captured the maximum tonal range and separation possible ‘in-camera’.

36. The Purpose Of The Tutorial And Conclusion

Shadows are the foundation of all photographs, giving the picture strength, structure, and depth. They are critical. We need to make a choice at the camera regarding shadow quality ~ home is too late. The easiest solution is enhancing the shadows using software ~ but accept this never creates quality. Or, we must expose additional frames to capture perfect shadow quality and accept the extra work involved in blending the shadow and highlight exposures together.

Interpolation Explained

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