Workshop created for Arteveldehogeschool Gent

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Zone system in the digital age.

What is this workshop all about.

This workshop will give you a better understanding of light metering, the dynamic range of your camera, the limits in dynamic range in digital camera’s and how to deal with extreme light situations.

An important limiting factor in capturing a high contrast situation is the dynamic range of the image sensor of our camera.

A better understanding of the different aspects of light metering, exposure, contrast ratio etcetera, will allow students to better evaluate when special exposure techniques will be needed to capture a scene. This workshop is based on the knowledge within Ansel Adams’ Zone system. This knowledge was developed in the film-age of photography, but is ‘with some re-thinking’ perfectly applicable in the digital age.

Workshop created for Arteveldehogeschool Gent

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The basics of light metering.

In this part of the workshop you will generate a series of images, and then answer some simple questions in order to get up to speed in your knowledge about light metering.

• Work in automatic white balance mode

• Work in Aperture priority

• Work in a low ISO setting

• Use the same aperture for all images

• Work in RAW

• Use spot or central metering

Exercise 1

Take a light metering on a grey card 18% grey.

Make an image with the light meter set at zero. (no exposure compensation).

Look at the histogram.

Where is the histogram positioned? Somewhere near the middle of the histogram scale

Why is the histogram not a single line, that would be logic since we photograph one single colour tone?

What does it mean if the peak in the histogram is not perfectly in the middle?

What does it mean if the RGB channels are not well aligned?

Slight tonal differences within the grey card and lens vignetting causes the peak to have some wider appearance as it would have with a single tone

Your camera’s light meter is slightly in-correct (at least if you have checked that your exposure is set at 0.

The white balance setting of your cam-era does not correspond with the light source you are working in.

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Excercise 2

Make a picture of an evenly lit white surface, make sure the white surface covers the entire photograph. Be careful not to cast any shadows on the surface.

Take a light metering and expose at 0 exposure metering

What does the histogram look like? Why is the peak not positioned to the right?

Our cameras measure reflected light, and are programmed to use a total exposure value that results in medium grey. Whatever grey tone we photograph with our exposure com-pensation set at 0, the result will always result in a medium grey exposure.

Add a 18% grey card to the scene, use the same metering as before and make an image. What does the histogram look like? What tone does the grey card have in your image?

The histogram shows two peaks, one in the middle, one at the left side of the histogram. The grey card looks dark dark grey.

Now take a light metering on the grey card, and make an exposure. How many stops differ-ence you have in your shutter speed? What does the histogram look like now? What does the gray card look like in your image?

The histogram shows one peak at medium grey, one peak in the highlight zone. The expo-sure is 2 stops different compared to the previous image. The grey card looks correct.

Add a black surface to the image, measure the light on the grey card, and make the image. What does the histogram look like? What tone does the grey card have in your image?

The histogram shows three peaks, one in the middle, one at the left side, one at the right side. The grey card looks correct.

If you look at this last image, which contains black, grey and white, you’ll see that the cam-era is well able to capture this tonal range. Why would there be a problem with the dynam-ic range if your camera can capture all tones from black to white?

This image contains black and grey and white, but every grey-tone has been photographed in the same light circumstances. If you use direct light to your white surface, and you would put your black surface in a shadow area, the dynamic range of the scene will further ex-pand, and eventually reach or surpass the dynamic range of the camera.

Workshop created for Arteveldehogeschool Gent

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Excercise 3

Make your own zone scale. Work in manual exposure mode and work on a tripod for this excercise!

Find yourself a bright, non coloured surface with a subtle structure. (I will use white woven wall paper as an example) Make an image at the indicated light metering. You will get a medium grey reproduction of the wallpaper but that is ok. Make a bracketing series in full stops up to 5 stops over- and underexposed. You will get 11 images in the end. (if you want to work more precisely, you could make an image every 1/3 of a stop in stead of working in full stops)

Import the images in Adobe Lightroom or any other RAW-development software.

Neutralize the white balance in the first image and synchronize all images.

Redevelop all images into a correct exposure: the 1 stop overexposed image will get -1 in the exposure slider, +2 stops overexposed will get -2 in the exposure slider. … At the end all images should look equally exposed.

Note from what exposure on (overexposed images) you get totally blown out zones in your image (evenly grey without detail). This is the point where your sensor is overexposed be-yond repair (clipping). Find out what is the last exposure that gives good results after RAW developing. This is your sensor’s limit for overexposure. (lets assume your image looks ok in the +3 exposure, clipped in +4 exposure)

Note from what exposure on (underexposed images) you get too much image noise to be able to discern the original woven structure. This is the limit for image detail in under-ex-posed areas. (lets assume your image looks more or less ok in -4, not ok in -5 stops expo-sure)

From the assumptions made in the previous paragraphs, this camera’s dynamic range is 7 stops, with limits at -4 stops underexposure and at +3 stops overexposure. Some cameras have a wider dynamic range, some cameras have a smaller dynamic range.

-5 to + 5 bracketing series for camera dynamic range test, before and after developing.

The Zone System developed by Ansel Adams.

Look here for more information on Ansel Adams: https://en.wikipedia.org/wiki/Ansel_Adams

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Ansel Adams and his contemporaries had no feedback on the images they made at the mo-ment of exposure, they had no spot light meter as we had now, and only after developing the image they were confronted with eventual mistakes they made.

He developed an exposure value system that would allow adapting exposure settings and developing methods to the dynamic range found in the scene he wanted to photograph. It based on extensive research and strict methodology.

One of the important parts of the Zone system was the brightness scale he developed to define the different tonalities in the scene. He worked in ‘Stops’ the same way as we know them now, but the dynamic range of film was slightly smaller than what we can reproduce now in a digital camera. He rated the zones with several ‘landscape equivalent’ subjects as you can see in the scale below. Zone 5 or V is what we call middle gray. In this way he could define the number of ‘Stops’ in the scene, and adapt exposure and negative development accordingly. In this manner he could slightly expand/reduce the dynamic range of the used film in order to enhance the contrast in the resulting negative.

In the next exercise we will measure the different zones in a high contrast scene with our digital camera’s spot meter functionality. This will help us define the dynamic range of the scene, and compare this with the dynamic range of our cameras.

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Excercise 4

• For this exercise, look for a high contrast scene. This can be a landscape in the morning or evening, looking towards the sun, but it can also be a dark interior, with a window showing exterior light.

• Use aperture priority and use an aperture that you would use for photographing the sub-ject/scene (for example f/8.0)

• Use the lowest ISO setting for your camera.

• Use spot metering to measure the shutter speed values.

• Make a rough sketch of your scene so you can note down the shutter speeds.

• Take a meter reading in the area you consider to be medium grey in your image.

• This will be considered the Zone V in the zone system. Note the corresponding shutter speed. (1/400s in my example)

• Measure the brightest area in your image, and the darkest area. Note the corresponding shutter speeds. Measure some intermediate brightness values.

Write down the matching zones from the zone system.

• Calculate the number of stops of difference in your brightest/darkest zone compared to the zone V`

Workshop created for Arteveldehogeschool Gent

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Consider what options you have for optimizing your exposure. you can shift your exposure up or down to optimally use the dynamic range of your cam-era and develop your raw file accordingly You can decide that the dynamic range of the scene is too wide and demands the use of graduated filters or exposure bracketing + HDR software merging.

In the above image:

1/400s is zone V 1/800s is zone VI or +1 stop compared to the medium grey area 1/1600s is zone VII or +2 stops 1/15s is somewhere in-between zone 0 and zone I 1/2s is far below zone 0, I could define it as zone V -8 stops of light.

If I consider the total dynamic range in this scene (from +2 to -8) and compare this with the dynamic range of my camera (from +3 to -4) then I know I will not have any problems in the highlights, but in the shadows, every stop below -4 will not have enough information to cre-ate detail in the shadows.

I can enhance the detail in the shadows by increasing my exposure by one stop, since I have one stop of play in the highlight range of my camera, and thus enhance the shadow area’s with one stop. I still will have very dark shadows, but I also know that I do not ab-solutely need to have detail in the darkest areas between the rocks in the foreground. In practical terms this means that in stead of using the 1/400s shutter speed (corresponding with the area I want to have as middle gray) I will expose at 1/200s. This will over-expose my image with one stop.

In development I will reduce the highlight brightness with one stop, to get a correct rendi-tion of the highlights. My shadow areas will have better tonal values and detail definition, thanks to the brighter exposure. I can still further add light to the shadow areas to further enhance their rendition in the final image, but I know that the (now -7stops) darkest areas will still not have enough detail to get over the image noise in those areas.

High contrast scene final image after adapting exposure settings and development.

Workshop created for Arteveldehogeschool Gent

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What would be the result if I used a Neutral Density graduated filter of 2 stops and adapted my exposure +3 stops (1/50s)?

I could have decided to use a Neutral density graduated filter to darken the sky by two stops, and brighten the exposure by three stops. This would bring the -8 stops shadows in the -5 stop zone, and further enhance the shadow areas. I would need to bring down the exposure of the sky with one stop to compensate for the graduated filter.

Final note:

The most important exposure rule in digital photography is not to over-expose your highlights. With the knowledge about your camera’s dynamic range, you can

• Define the area in the image that should have the medium grey exposure. • Set your exposure at 0 and check the shutter speed in this area. • Check if your highlights fall within the highlight maximum of the dynamic range of your cam-era. (+3,xx stops compared to the medium grey area) • If yes, you are ok and can make the exposure, if no, you should adapt your exposure to pre-serve your highlights.