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Photographic Exposure Basics

Mesa  Arch, surnirse, Canyonlands, National Park, Moab, Utah

Landscape shot like this one of Mesa Arch require maximum depth of field requiring the smallest aperture possible. Shot at F22 @ 1/4 of a second. ISO 320

A bald eagle perched on post on a blue sky evening during a full rising moon in Grand Teton National Park

Whenever shooting wildlife is is important to stop all movement, this requires a high shutter speed which consequently requires a large aperture opening which limits depth of field, that is why the moon is out of focus. F/8, 1,000 of a second, ISO 400

Early in my photographic education the late, great Galen Rowell was my inspiration and this is a quote from Galen:  “I almost never set out to photograph a landscape, nor do I think of my camera as a means of recording a mountain or an animal unless I absolutely need a ‘record shot’. My first thought is always of light”. In the mid 80s he published a photography book called “Mountain Light that is still selling well today, every nature phtographer ought to read it.

One of the most important aspects of being able to communicate the essese of our vision through a photograph is the proper use of light. While there are  certainly  many other aspects of great photography, if the light is wrong, nothing else will work!

Nature photographers often speak about seeking out certain light conditions or only shooting in specific types of light. Light has a triple nature for the photographer to factor: color, direction, and quality. Photography is capturing light which is exposure.

Kayaker performs ender at taco hole on the Snake River
To capture spots action like Kayaker Steve Horn a high shutter speed is required and a corresponding large aperture to make up for the short duration of light from fast shutter

When we choose to shoot in auto exposure modes instead of manual mode we forfeit our judgement, when we forfeit our judgement we are outsourcing our thinking to a computer. Auto exposure settings on camera computers are great but they calculate input to achieve an average. Calculated algorithms are great for good results in average light but algorithms fail in extraordinary light.   Extraordinary light averaged by algorithms result in an average exposure at best however extraordinary dynamic light often defies algorithmic data sets.  Great photographs are nothing but extraordinary dynamic light. Learn to shoot in manual mode!

In the photographic process exposure is the total amount of light allowed to fall on the camera sensor during the process of taking a photo. This requires that a finite quantity of light reaches the sensor  so the photo is sufficiently exposed.

There are several ways to achieve the same amount of light to achieve good exposure.

Quantity of light = X

X = time value + aperture value

Time value and aperture value are your variables and each has a cost and benefit. Your subject will dictate your priority of selection

Aperture value is how big the lens opening is on your camera  F 5/6 – F8 – F11 etc., the higher the number the smaller the hole that lets in the light.

When you have a big hole (aperture) you can use a higher shutter speed to stop action, the price is less depth of field. Depth of Field – depth of field (DOF) is the portion of a scene that appears sharp in the image.

A smaller aperture requires a slower speed and often a tripod to keep the camera steady; the risk is a blurred photo. Conversely a large aperture facilitates shorter shutter speeds to stop action, the price is less depth of field.

Camera aperture diagram explained
Camera aperture diagram explained
Fly-fisherman, Green River Lake, Wind River Mountains
Shooting a sport like fly-fishing I would normally use a high shutter speed but this photo was also a scenic. Howard the fisherman cooperated and held impossibly still while I shot a small aperture opening possible to maximize depth of field requiring a slow shutter speed. I shot this at F/10 at 1/6 of a second, ISO 100. Today I would have used a ISO of 320 so I could have shot with a smaller aperture although this turned out fine.

Time Value = Shutter speed, the higher the number the faster the shutter. When shooting with a telephoto as we do for wildlife you will want a high shutter speed. A rule of thumb is to match your shutter speed to the length of you lens. A 300mm telephoto would need a minimum of 1/300 of a second. I try to double that when possible.

For sports and wildlife you need to stop action so you would want a fast shutter speed which normally requires a large aperture hole, which dictates a small number like F5/6.

For shooting scenics maximum depth of field is desirable dictating the smallest possible aperture   and a slow shutter speed. When the shutter speed gets below 1/60 it becomes necessary to us a tripod to prevent camera shake.

Now the curve ball – ISO

ISO stands for the International Standards Organization and the numbers are the camera’s sensitivity setting for light. The lower the ISO the better saturation your photos will receive but when the light diminishes increase the ISO setting only as much as you need to achieve the minimum shutter speed mandated by the shooting situation.  I hate to exceed 1200 ISO as it introduces noise (missing pixels) to your photo. Use high ISO’s with caution and with lower expectations. That said, every generation of DSLR the quality of higher ISOs  improves.

For those of you that used to shoot film high ISO/ASA settings don’t penalize your photos as much as they did back in the film days. Use them as needed, they are your friend.

Grizzly Bear cubs appear to be dancing while they wrestle in Grand Teton Natonal Park. Thest two year old cubs would forage for a while then wrestle for a while. These cubs are of famous grizzly bear sow #399 (© Daryl L. Hunter - The Hole Picture/Daryl L. Hunter)

This 2008 photo was shot in RAW, my software couldn’t process the wide dynamic range so I lost the highlights. A year later I upgraded software and saved the highlights because I still has the RAW file.

The case for shooting RAW

Like a photographic negative, a raw digital file has a wider dynamic range or than your JPG choice and it preserves most of the information of the captured image. The purpose of raw image formats is to save, with minimum loss of information, data obtained from the sensor.

Raw files retain all original data therefore in the future you can go back to the RAW file when you are more proficient in post processing and readjust the file.  Conversely JPG files are processed in your camera and as soon as your camera’s computer computes your averaged image, the computer throws all information the computer deems unnecessary away never to be available again.

In summary, serious photographers learn to shoot in manual mode because they demand to be in command of the light!





6 thoughts on “Photographic Exposure Basics

  1. Mac McMillen says:

    Great article and beautiful supporting photos!

  2. Montclair Jesperson says:

    Good foundational principles for a newby like me.

  3. Karen Millen says:

    Good day! I thanks for posting these easy to understand rules of thumb about photography, you have made the complex – simple!

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