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Metering and Exposure Compensation

August 13th, 2019

There are several camera settings that allow us to control or adjust how a scene is metered. 

Most middle to upper end cameras include several metering mode options that control how much and which parts of a scene are used to assess the light intensity. The most basic of these metering options uses the entire visible scene to evaluate the exposure; this mode gives equal weight to the middle, edges and corners of the scene. Another mode, sometimes called spot metering, only uses the center of the image, sometimes the spot is as little as 1% of the total scene. Most cameras that include the ability to adjust metering have other options that fall somewhere in between these two modes. 

Using the appropriate metering mode for the subject that you are shooting will help you get closer to an optimal image. For example: when shooting a wide landscape I probably would want to use a mode that takes into account the full scene. On the other hand when shooting an event where there is a strong central subject (see Faceplant below) I would most likely use spot metering to ensure the exposure on the subject was spot-on and not care about the less important edges and corners.

(Faceplant, Oakley Rodeo; Canon 5DMII, EF70-300 @ 135, 1/125s, f6.7, ISO 6400)

Another option to control the metering of a scene is exposure compensation. As I stated previously, by default the camera attempts to achieve middle grey for the exposure. Using the exposure compensation setting allows you to tell the camera to purposefully under or over expose an image. 

The exposure compensation setting is frequently present on the camera as a dial labelled -2, -1, 0, +1, +2. Setting the camera to 0 (zero) allows the camera to do it’s default thing and try and adjust to middle grey. Adjusting the dial to -1 tells the camera to adjust the target from middle grey to one full stop darker. (Recall one full stop is a halving/doubling of the light.) Conversely, adjusting to +1 will tell the camera to make the image lighter by one full stop. When shooting a winter snow scene using a setting of +1 or +2 will ensure that the snow is rendered whiter than middle grey.  

(Canon 5DMII, EF16-35 @ 30mm, 1/1000s, f6.3, ISO 250)

Understanding how your camera interprets the light intensity of a scene is the first step to achieving a keeper image. Using the most appropriate metering mode and, if needed, adjusting the exposure compensation setting will help get you closer to expressing your vision. 

Metering to Middle Grey

August 6th, 2019

When you point your camera at a subject with the camera in auto mode it evaluates the various light intensities across the scene and attempts to determine the proper settings to achieve a balance between the light and dark regions. It tries to determine settings that will produce middle grey in the resulting photograph. 

Middle grey is a tone that is perceptually about halfway between black and white. Middle grey is defined as a tone that reflects 18% of visible light. Oddly enough green grass and blue skies both translate to values very close to middle grey.

This photograph by Charles O’Rear illustrates my point. (The image was used by Microsoft as the desktop background for Windows XP. Due to the pervasiveness of Windows XP this might be the most viewed photograph in the history of photography.)

Here it is again converted to black and white using the saturation slider in Lightroom.

The tones in the sky and grass are very similar and close to middle grey (some variances exist but hopefully you get my point). 

Letting the camera do it’s thing and adjust to middle grey works great most of the time but middle grey isn’t always desirable. Sometimes you want your photograph to be lighter than middle grey. If you’re shooting a winter snow scene allowing the camera to produce middle grey is going to result in grey snow which doesn’t match our expectations and will result–most of the time–in an unappealing image. On the other hand if you’re shooting the night sky and the milky way, allowing the camera to auto adjust to middle grey is going to render the blackness of empty space too light, again resulting in an inaccurate representation of what our eyes see and most likely an unappealing image.

Next week I’ll talk about two of the settings that allow us some control over how the camera adjusts to the light intensity on the subject we’re shooting.  

Intensity

July 30th, 2019

Our eyes are amazing organs and can see a huge range of light intensities. A snow field on a bright sunny day is near one end of our visible range while a moonless, overcast night is at the other. 

Light intensity is measured in candelas which is defined as the luminous power per unit solid angle emitted by a point light source. Whatever! To a non-physicist that probably doesn’t make much sense; as photographers how do we make sense of light intensity? 

In photography light is measured in stops rather than candelas. A stop represents a halving or doubling of light. (I’ll discuss stops again in subsequent posts. For now I just want to introduce the concept.)

Measured in stops our visible range is about 30, which mathematically corresponds to a billion candelas since two to the thirtieth power is about a billion (2^30 = 1,073,741,824). In the graphic below our full visible range in stops is represented by the black number line. 

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We can see an incredible range of light intensities but not all at once. Our eyes adapt to the current intensity of ambient light but at any one time we can only see just under half the full range of 30 stops; or about 13 or 14 stops of light (represented by the red line in the graphic above). 

Our ability to see a wide range of light intensities is referred to as ‘dynamic range’ and is controlled by our pupils which open or contract to allow an appropriate amount of light in. At any given time our eyes adjust to give us the most visibility by averaging the light intensity over a scene and adapting to that average. We might lose the brightest and/or darkest areas but we see the majority of the scene. If we move our focus to another region of the scene, perhaps to a darker zone, our eyes adapt by opening the pupil to allow more light to come in helping us to see in the darker areas but by doing so we lose visibility into the brighter regions.

Cameras work in a similar way to our eyes with the aperture acting like our pupil to control the amount of light reaching the film or sensor. But while our eyes can see about 13 stops of light, cameras can only see 10 or maybe 11 stops of light (represented by the blue line in the graphic above).  (The better cameras on the market today can see about 10 or 11 stops of light; lower end cameras have a much more limited range and might only see 6 or 7 stops of light.)

If the dynamic range of light in a scene exceeds 13 stops, the brightest or darkest areas block out and we can’t see any detail in those areas. The same is true with a camera; areas in the scene that exceed the dynamic range of the sensor will block out and be rendered either white or black with no details. 

This image was shot with my cell phone which has a limited dynamic range. The orientation is looking south with the sun just out of the frame. The bright sky was rendered completely white and the crack in the rocks below the back tire of my bike is completely black; both lack any detail whatsoever. 

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(LG G6, 1/800s, f1.8, ISO 50)

For comparison, this next image was shot at the same time and location but this time looking northwest. In this image, with the sun at my back, the scene is more evenly lit and it has a narrower dynamic range; one that is within the abilities of the camera’s sensor. In this image the sky is rendered blue and the crack in the rock has some detail. 

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(LG G6, 1/640s, f1.8, ISO 50)

Understanding the intensity of light and your camera’s abilities and limitations to capture that range of light is foundational. Using that knowledge to capture an image that conveys your mood and interpretation of the scene is what being a photographer is all about.

Light Color

July 23rd, 2019

The light’s temperature or color is the first characteristic of light that we have to address within the camera’s settings before we shoot. The setting is called ‘white balance’ and typically has options for ‘daylight’, ‘incandescent’, ‘florescent’, ‘cloudy’, etc. Each of these settings attempts to modify the camera’s interpretation of the scene and compensate for the color of the light based on an average of ‘cloudy’ (or whatever) light color.  They do a decent job but the problem with these settings is that there are only a handful of them and actual light temperature/color is a massive range (Lightroom supports values from 2000 up to 50,000). (Most cameras have an ‘auto’ white balance setting and from my experience it seems to do a decent job under normal conditions.)

A better way to address white balance is to set your camera to capture in ‘raw’ format and address the matter in post processing. Not all cameras can store images in raw format so this may not be an option for you. Once you choose to save in raw format the white balance setting can be ignored (still it’s probably best to set it to ‘auto’) and all color correction can be performed in post processing using software. While this process relies on you the editor to visually get the right color balance you’ll probably be able to tune the image better than using only the handful of settings built into your camera. 

The best way to address white balance is to capture in ‘raw’ and include a ‘color card’ in a test shot of the subject. Color cards are small 3x5ish items that include a number of small squares of precise reference colors, including true white. The test shot can then be loaded into your post processing application and the color card can be used to set the reference for true white. The software then chooses the right white balance to achieve true white for that square on the color card. The white balance settings can then be quickly duplicated across the other images in that shoot. This process, while a bit more fiddly, ensures an accurate and precise white balance setting. If you need a high degree of color accuracy in your images, this is the way to go. 

(A quick search at Amazon for “photo color checker” turns up a long list of color cards, several that include more than one ‘white’ which can be helpful to fine tune the white balance.)

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(Rio Grande Depot, Salt Lake City, UT; Canon 5DMII, TS-E45, 1.6s, f10, ISO 400)

(White balance adjustments can be made on a non-raw image (jpg, etc.) but are not as extensive as with raw format images. If your camera can’t save in raw format your best option is to get as close as you can in-camera and then fine tune the color balance in software.)

Light Temperature

July 16th, 2019

Lastly, we need to understand the temperature of the light source. Defining light as having a temperature is confusing, unless you’re a physicist; we really should call it color which is more relevant to our experience of it.

Let’s talk about temperature first. One of the definitions for red-hot is ‘glowing with heat’; white-hot is defined as ‘being at or radiating white heat’.  These terms (red-,  white-hot) are in our lexicon and come from experiments with hot metals which glow different colors depending on how hot they’re heated. At about 2500K a metal object glows with a yellow-white color while at 5500K it will glow blue-white. (K stands for Kelvin and is a temperature scale that starts at absolute zero.)

Some common temperature approximations are 7500K for shade, 5500K for daylight and 2750K for sunset. 

The temperature of the light matters if you’re trying to accurately duplicate the colors of your subject in your photograph. If you’re photographing a room in a house with white walls you don’t want the walls looking blue or yellow or green, they need to be white. The same is true for skin tones; your client won’t be satisfied with your portraits if their skin is orange or some other weird tint.  

It’s especially challenging when capturing two different light sources in the same image. This image of my sister’s dinning room illustrates the problem. Outdoors there is hazy sunlight and the light has a blue tint (high temperature) while inside the light is from an incandescent bulb with a warm yellow glow (low temperature, note: the warmth is accentuated from the wood tones and yellow walls). 

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(Canon 5DMII, EF24-105  @ 28mm, 1/60s, f8, ISO 100)

Light Sources

July 9th, 2019

Having considered the direction of light, next let us focus on the light source. 

The source of light illuminating our subject can be either a point of light or a diffuse curtain of light. The most common source of light that is a point, is the sun. (The sun isn’t a point, its actually rather large but it’s so far away that for our purposes it appears to be and acts like a point source.) Sunlight on a clear day creates a hard separation between areas illuminated by the source and areas that are not directly illuminated, i.e. shadows. Such light is often referred to as hard or harsh lighting. 

(Canon 5DMII, EF24-105 @ 105mm, 1/320s, f18, ISO 400) 

The other option is a diffuse light source which softens the light transitions and creates a very evenly lit subject with minimal or no shadows. A perfect example of a diffuse light source is a cloudy sky. As you might suspect, this type of light is referred to soft light. 

(LG G6,  1/30s, f1.8, ISO 200)

Of course there is a whole range of light sources in between these two extremes that can provide a wide variety of light-to-dark transition abruptnesses. As the photographer it’s up to you to decide what light source best illuminates your subject and conveys the feelings you have about it. 

Characteristics of Light

July 2nd, 2019

The idea of photography being the practice of capturing light interacting with a subject encourages us to consider several characteristics of light and how it affects the subject. Three that we must consider are direction, source and color.

First off we should consider the direction of light relative to our subject. The light might be in-line with the lens of the camera (axial light) and either illuminating the subject from the front or from the back. 

Front light creates a (relatively) even distribution of light and allows full illumination of a large part of your subject. 

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(The Bedhouin, Canon XSi, EF-S15-85mm @ 22mm, 1/1000s, f5.6, ISO 800)

On the other hand backlight can create strong shadows and highlights. The setting sun backlit these light-rail tracks on 4th South in Salt Lake City. 

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(4th South Trax, Canon XSi EF-S55-250 @ 163mm, 1/125s, f13, ISO 100)

The reflected highlights off the rails and the building shadows created a range of light (the difference between dark and light) that exceeded the capabilities of my camera and I had to choose settings that captured my mood and impression of the scene.  

We can also use side light to illuminate our subject. Side light gives shape and volume to a subject accentuating shapes and textures. These domes on the Sheikh Zayed Grand Mosque in Abu Dhabi gain volume and shape due to the side lighting. 

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(Canon XSi, EF70-300mm @ 300mm, 1/125s, f8, ISO 100)

Textures come to life under side lighting which accentuates the minor surface variations with light and shadows. While walking around the Mosque in Abu Dhabi I found this amazing relief and wanted to photograph it. Unfortunately, at the time I first saw the wall the light was axial and the texture all but disappeared. I came back later in the day when the sun had moved around to the side and captured this image where the texture really pops out. 

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(Canon XSi, TS-E45mm, 1/250s, f6.7, ISO 100)

Of course the light source might be at any angle relative to our subject and as it moves relative to the subject, or the subject moves relative to it, the light accentuates or masks various properties of our subject. Understanding how the direction of light affects the mood or interpretation of a subject is fundamental to expressing your vision. 

Drawing with Light

June 25th, 2019

Since this is a photography blog maybe I should talk about photography for a while.

The word photography comes from Greek roots that mean ‘light’ (photo) and 'draw’ (graphic); which combined mean 'drawing with light’. That definition is somewhat misleading in that a photographer doesn’t really draw with light as much as they capture light interacting with a subject to create a drawing. For me, thinking of photography in that light (pun intended) is more useful because it encourages me to think about my subject, the way light is interacting with it and possible ways in which I could modify that interaction. 

Light interacting with a subject could be as simple as soft light falling on the petals of a rose…

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(Kate’s Rose, LG G6, 1/320s, f1.8, ISO50)

or something more complex like the light from fireworks interacting over time with the waves of a pond.

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(Evelyn’s Birthday Party, Canon 5DMII, EF24-105 @ 99mm, 4.0s, f8, ISO100) 

Simple or complex, capturing fleeting moments of light interacting with the world around us is what photography is all about. 

Does how you think about light influence your photography practice?

Balloons from the Inside

June 18th, 2019

I’ve been to several balloon festivals over the last few years. The pilots and crew are incredibly friendly and accommodating to photographers, as long as you stay out of the way. 

The envelopes (the balloon part) can be really colorful and fun. I especially like looking into the balloon while it’s partially inflated and still laying on the ground. There’s an abstract-ness I find captivating and the backlit colors from the early  morning sun really pop to make a great image (in my opinion anyway). 

I’ve got this image, and a few more, over on my web site. You can find them here…

https://www.kirkmarshallphotography.com/balloons

Have you been to a festival?

(Canon 5DMII, EF16-35 @ 23mm, 1/350s, f13, ISO800)

Balloon Flight

June 11th, 2019

While we were in Cappadocia we took a flight in a balloon. I’ve got to admit I thought the price was a bit steep and didn’t feel like it would be worth it. Boy, was I wrong; it was amazing. 

We had to wake up at some ridiculous hour, like 5am, and stand around in the cold breeze while they inflated the envelope and got ready to fly. But once we got off the ground, the breeze stopped, cause we were drifting along with it, and we floated silently over the landscape. I was giddy. I’d jump at the chance to do it again; it was totally worth it!

Here’s an image I shot while we were flying.

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(Canon 5DMII, EF24-105 @ 105mm, 1/125s, f16, ISO100)