Heat distortion can ruin photos taken with a zoom lens

Article written by Kevin Lisota

Have you ever taken a photo with a long zoom lens where you thought your technique was perfect, only to come home and see a image that is mushy and and seemingly out of focus?

Moonrise over Seattle and the Cascade Mountainss ruined by strong heat distortion when cold air above the waters of Puget Sound mixed with warm air on a summer-like winter afternoon. 500 mm, 1/3 sec, f/10, ISO 80.

Moonrise over Seattle and the Cascade Mountainss ruined by strong heat distortion when cold air above the waters of Puget Sound mixed with warm air on a summer-like winter afternoon. 500 mm, 1/3 sec, f/10, ISO 80.

This happened to me when shooting a moonrise over Seattle this week on an abnormally warm winter day. There was nothing wrong with my lens, focus or tripod support, but the big temperature difference between the cold water of Puget Sound (~47 °F) and an very warm air (~75 °F) caused heat distortion that ruined my photographs.

You’ve probably seen heat distortion on a hot summer day, where there are waves of heat rising from a road. Or perhaps you have seen it in the exhaust from a boat, train or airplane.

Years ago when I first came across it in my photos, I thought it was either something wrong with my technique or equipment, but no amount of fancy gear or flawless camera technique can fix photos ruined by heat distortion.

I shot this photo of Seattle’s Space Needle at sunset this week. My 500 mm lens is razor sharp at distance, the camera was in perfect focus and was on a sturdy tripod with the shutter triggered by a timer. Both the equipment and technique were perfect, but the resulting image is a squishy mess.

Strong heat distortion of Seattle skyline taken from over 7 miles of water. Air temperature ~ 75 °F, water temperature ~47 °F. 500 mm, 1/400 sec, f/9, ISO 1250.

Strong heat distortion of Seattle skyline taken from over 7 miles of water. Air temperature ~ 75 °F, water temperature ~47 °F. 500 mm, 1/400 sec, f/9, ISO 1250.

When will heat distortion occur?

Heat distortion is caused when light is refracted through air of differing densities. Hot air is less dense than cold air, so light waves are bent differently in hot versus cold air. The result is visible heat waves when there is a significant temperature difference between the ground and the air above it.

On a hot, sunny summer day, you will see this above roads, but it can occur on just about any land mass where the sun heats the ground to a temperature higher than the surrounding air such as an open field or beach.

Bodies of water can cause the exact same phenomenon when the water is either significantly warmer or colder than the air above it. A warm ocean with cold air above it may show heat distortion and so will a cold ocean with warmer air above it.

Cold 38 °F air over Puget Sound at 50 °F causes heat distortion.

Cold 38 °F air over Puget Sound at 50 °F causes heat distortion.

Heat distortion is not restricted to hot summer days. It can also occur in arctic temperatures during winter where the sun warms the land or mountainside to a temperature well above the air temperature.

Distance makes heat distortion worse

The further away the subject of your photograph, the more heat distortion will be present. The further distance means that the light is travelling through more air before it reaches you, therefore it gets refracted more in areas where heat distortion is present.

A long zoom lens usually means you are trying to photograph subjects at a greater distance. That greater distance increases the chance that heat distortion can ruin your images. Heat distortion is most prevalent at ground level.

Heat distortion is more prevalent near ground level. Notice the strong heat waves above the water, but a sharper view of Mt. Rainier above those heat waves.

Heat distortion is more prevalent near ground level. Notice the strong heat waves above the water, but a sharper view of Mt. Rainier above those heat waves.

Zoom lenses have the added disadvantage of bringing the detail of the heat waves closer, making the result larger and more obvious in your photo. Photographers who spend more than $10,000 on a monster 600 mm or 800 mm prime lens will want to remember this before getting angry and wanting to send the lens back for repairs.

This photo shows a ferry that is ~1 mile away from my camera, taken at 200 mm. Focus was perfect on the ferry, but there is some softness due to heat distortion. The city in the background is ~7 miles away. The heat distortion is very severe at the greater distance since that light has to travel through more refracted air.

Heat distortion is slight on the ferry 1 mile away, but severe on the city that is 7 miles away. 200 mm, 1/320 sec, f/9 ISO 1250.

Heat distortion is slight on the ferry 1 mile away, but severe on the city that is 7 miles away. 200 mm, 1/320 sec, f/9 ISO 1250.

How can you avoid heat distortion?

In many cases, heat distortion is unavoidable and there is nothing that you can do to fix it, but there are a few different ways to avoid it.

  1. Move closer to your subject. Reducing the distance that light travels through the refracted air will reduce the amount of heat distortion that you see in photographs.

  2. Avoid photographing over surfaces that are easily heated up by the sun, such as a road, beach or similar.

  3. Shoot near sunrise before the ground has heated up or near sunset once the ground has begun to cool. There is less or no heat distortion during these times.

  4. If photographing over a large body of water, try to take photos when the air temperature is similar to the water temperature.

Soft, out-of-focus images can be caused by poor technique or the wrong camera settings, but once you have ruled those out, don’t forget about heat distortion.

Focus to infinity – The Key to Nighttime Star Photography

Milky Way over Ruby Beach in Olympic National Park

Milky Way over Ruby Beach in Olympic National Park

Photographing the stars at night can reward photographers with stunning images, but it can be challenging to operate the camera in the dark of night. One of the keys to a great shot of the stars is making sure that they are in focus.

Focusing a camera in the dark can be difficult for both you and the camera. Camera focus systems rely on contrast between bright and dark areas of the photo to achieve focus. Under a dark, moonless sky, there simply isn’t enough light for your camera’s auto focus system to work. Using your eyes and the viewfinder won’t be any better.

Sharp stars mean that your lens is focused to infinity where objects at an infinite distance are at their sharpest. On a manual-focus lens, this may be as simple as turning the focus all the way to the hard stop at the infinity symbol ∞. (More on this later.)

Auto-focus lenses can be tricky. Modern auto-focus lenses all focus past infinity, so there is no hard stop on the focus ring, and once you go past infinity focus, your photos will not be sharp. There are a number of reasons for this. The camera’s auto-focus motor is fast and needs room to move in and out without a hard stop. Changes in temperature and changes in focal length on zoom lenses also mean slightly different spots for focusing to infinity.

Here are some techniques to focus to infinity for your next photography adventure under the stars.

Decide on your focal length

If you are going to shoot the stars with a zoom lens, be sure to set your preferred focal length prior to focusing the camera.

Ideally your zoom lens would be “parfocal,” meaning that focus doesn’t change as you zoom in and out. The reality is that most zoom lenses are “varifocal,” where focus changes as zoom magnification changes.

If you are using a 16-35 mm lens, for example, focus at infinity for 16 mm might be slightly different than at 35 mm.

Manual focus lens

A manual focus lens will have a hard stop at infinity focus. In many cases, it may be as simple as turning your focus ring all the way to infinity.

However, manual focus lenses are not always perfect, so it pays to check the sharpness of your stars with actual photographs and make minute adjustments to the focus ring if necessary.

Compose Using Daylight

One of the best ways to set your focus to infinity also requires the most preparation time.

If you arrive at your scene when there is still daylight, even twilight, it allows time to focus your lens on a distant object like a mountain, tree, building or horizon. Move your focus point to the center of the lens, and focus on the most distant object that you can.

Once you have achieved focus, turn your camera to manual focus mode. I find the physical levers or switches for manual focus to be easiest, but you may have to change the focus mode in your menu system. Securing the focus ring on your lens with a piece of gaffer tape can help prevent you from bumping the focus later at night.

Arriving early enough so that you can see the scene gives you the added opportunity to look for compositions of the sky that include foreground objects like trees, rocks or mountains. It is quite difficult to make these composition decisions when you are in a pitch-black environment.

Take a picture of the focus ring on your lens

Many lenses have a focus distance scale viewable through a window on the top of the lens. Having a snapshot of this scale at infinity focus can help you set the proper focus in the dark by moving your lens’ focus ring to that point on its focus scale.

If you are using a zoom lens, set the focal length that you plan on using to shoot the stars. During daylight or twilight hours, focus the lens on the most distant object you can, then take a snapshot of the focus distance scale on your lens.

As an example, my Nikon 14-24mm lens looks like this when focused at infinity, with the focus point to the right side of the infinity symbol ∞.

Nikon 14-24mm focused to infinity

Nikon 14-24mm focused to infinity

It is important to do this with the exact lens/body combination that you plan to use, as even lenses of the same model might be ever-so-slightly different than one another due to manufacturing tolerances.

Focus on the Moon

If there is a moon in the sky, even a sliver of the moon, use it to focus. The moon is extremely bright, is at an infinite distance and is easy to focus on, even at night, for most auto-focus systems.

Lunar Eclipse – January 20, 2019

Lunar Eclipse – January 20, 2019

Once again, put your focus point in the center of the frame. Put the focus point on the bright part of the moon and focus, either using auto or manual focus. For auto-focus, it will be easiest if you focus on the edge of the moon, which has the most contrast.

Find or Create a Distant Light

A street light, building lights or car headlights in the distance can be bright enough to focus on, so make use of them if they are present.

Of course if you sought out the darkest skies, there may be no option for distant lights. If you have a bright flashlight, use it to illuminate the farthest object that you can and focus on that.

Further away is better, but for a wide angle lens, you should be able to focus at infinity with an object that is at least 25-30 ft or 8-10 m away.

Another option might be to turn on your phone’s flashlight and prop it up somewhere in the distance, then focus on that.

Fiddle with Manual Focus

You snapped a photo of your focus ring at infinity focus like I described above, correct? If so, pull up that snapshot and use your flashlight or headlamp to set the focus ring to that same spot.

Even if you don’t have a snapshot, set the lens at its infinity mark and use trial and error to achieve focus on the stars.

To make the process go faster, crank up your ISO setting as high as you can, say 12,800, 25,600 or higher. This will give you very noisy photos that you aren’t going to keep, but it will enable you to take quicker exposures.

Take a photo, then zoom in as far as you can on the image and look at the size of the stars. You want them to be as small and sharp as possible, not soft blobs of light.

Make very minute changes to your focus ring, take another shot and zoom in on focus again. This process can take a little time, but you can often nail focus with just a few test shots.

Out-of-focus stars

Out-of-focus stars

Confirm Focus Throughout the Night

If you are shooting during an extended period at night, be sure to periodically check your focus by zooming all the way in to your photos on the back screen of your camera to check the focus of the stars, in case you have bumped the focus ring of your lens.

Star photos can look awesome on the back screen of your camera when not zoomed in, but you may get home and be disappointed by your stars when you see the photos larger on your computer screen.

Night photography can be tricky when first starting out, but is very rewarding when you get the hang of it. Keep practicing and the process will get easier every time.

Blog Post Written by Kevin Lisota

Winter Photography Tip: avoiding lens fog

Photo Credit: Kevin Pepper, 2018 Yukon Workshop

Photo Credit: Kevin Pepper, 2018 Yukon Workshop

Let’s take a look at why lenses tend to fog in cold weather. This is something that we constantly teach on our winter workshops during the winter months.

When the air near the lens is cooled by the lens, the relative humidity of the surrounding air will increase. This is because when air cools, it loses its ability to carry water vapor. Once the relative humidity increases enough, water will begin to collect on the lens. Even if the air is fairly dry, when the temperature difference is great enough you will get lens fog.

So how do we stop this? One way is to use hand warmers and place them on the barrel of the lens. This will warm up and dry both the external glass and the internal elements, help staving off mold that could grow inside your lens.

Another method we like, is to use your coat that you wore outside. The outside of the coat is the same temperature as the lens and camera. Take that coat and wrap your camera so the outer shell is against the camera. This allows the camera and lens to warm naturally, surrounded by air that is initially cool—both the air and camera gear will warm naturally, preventing the moisture and fog from forming on your camera gear.

If you have any further comments, please add them to the comments section below. The more feedback and ideas the better.

The Human Element Can Create a Powerful Image

Photo Credit: Andy Williams, 2017 Yukon Photo Workshop

Photo Credit: Andy Williams, 2017 Yukon Photo Workshop

Did you know that people like to live vicariously through human subjects in photos?

Adding a human element will create more emotion to an image. It makes them feel like they are experiencing the location themselves.

How do you accomplish this? By posing the subject in such a way that they either become anonymous, or a focal point in the image.

The human element also gives a better sense of scale. By placing your subject in the distance, you can get a better sense of just how big those mountains really are, how tall a waterfall really is, or how much of the sky the aurora is taking up. This photo is an example why photographing “tiny” people in large landscapes does well.

Adding a human element to photos helps tell a story. Images seem to be more powerful when people are included in them.

You can completely change the storyline of a particular photo depending on what type of human element you decide to incorporate—large and a focal point, or small and blend them into the landscape.

Why don't you join us on one of our workshops? We lead trips all over the world and would love to share some of our favorite locations with you.

Photographing the Falkland Islands, South Georgia, and Antarctica

willbl-1.jpg

Few places on Earth are as remote, or as inhospitable to life, as Antarctica and the Subantarctic Islands.

Will Burrard-Lucas recalls, “On first visiting this frozen land, the sense of being a visitor to an alien world was almost overwhelming. As a photographer, how could I start to convey the essence of this place through images alone? How could I capture the sense of wilderness, the abundance of wildlife, the harshness of the environment and staggering beauty of the landscape?”

Now, after several trips to region, Will feels like we has started to chip away at this challenge. So, to help our group of future Antarcticans that join us on our expeditions, he decided to share some of the lessons he has learned after numerous trips to Antarctica and the Subantarctic Islands.

With so much wildlife, interesting behavior is all around

willbl-4.jpg

Being confronted with a penguin colony can be sensory overload. In every direction busy birds can be seen going about their days—building nests, tending eggs or chicks, chasing off predatory skuas, and squabbling with one another. Knowing which point to point your camera at can be a tremendous challenge!

In these situations Will says he learned to pick out a few birds and then just wait and watch. By being patient you will find that natural behavior unfolds in front of you and when it does you will already be in the perfect position to capture it.

Something else happens as well—the birds in these places have no innate fear of humans, and so are actually quite inquisitive. If you sit down and remain still you becoming even less threatening and often birds will come up and check you out. Penguins will also start pecking at your sleeves and shoelaces! This makes for great wide-angle portraits.

Capture portraits with personality

willbl-2.jpg

Few birds are as interesting and fun as penguins. So try to capture their personalities in your photos. The single most important thing you can do to capture impactful wildlife portraits is to get down low, on the same level as your subject. For penguins this either means lying down in the snow or flipping out the screen on your camera and holding it down below your knees. The low perspective not only helps the viewer connect with the animal, it also moves the background out of the plane of focus, which isolates your subject and helps make it “pop”.

To capture a successful portrait, you need to make sure your focus is spot on. For animals, this means making sure the eyes are tack-sharp and then selecting an aperture to give you the depth of field you need. If I’m photographing a single animal, I often shoot wide open to get a shallow depth of field and isolate my subject. Penguins hop around surprisingly quickly and with a telephoto lens, you don’t have a lot of leeway in terms of focal plane. I therefore recommend shooting in continuous auto-focus mode and placing a single focus point over the eye so that the focus is continually updated until the moment the shot is taken. This means you have to practice moving your focus point around the frame quickly in order to recompose your shots. Sometimes cameras might mis-focus slightly, or the animal might blink and you might not realize this at the time—and so, Will recommends capturing 2 or 3 shots at a time just to be safe.

It’s not just the about wildlife but the habitat as well

willbl-18.jpg

It was the wildlife that first drew Will to Antarctica, but it was the landscapes that blew him away; imposing jagged peaks, glaciers tumbling into the ocean and beautifully sculpted icebergs set a spectacular stage. Whenever possible look for scenes where You can show the animals in their environment. Often this means trading the telephoto lens for a 70-200 or 24-70. These will be the type of images that capture the essence of Antarctica.

The weather can be a challenge but also an opportunity to capture something different

Wind

The weather in this part of the world can be both unpredictable and extreme. As a result, you never quite know what today, or the next day, has in store for you. Rather than being an inconvenience, Look at the diverse weather as an opportunity to capture interesting images. Maybe it is fierce wind whipping snow over the crest of a hill, giant snowflakes drifting down over a penguin colony, rough seas pounding against the base of a tabular iceberg, or a ray of sunlight melting the snow on a mountainside. Whatever the conditions, it is the varied weather that makes every trip to the region different and gives a unique twist your photos. Embrace it!

Will Burrard-Lucas is a wildlife photographer. He leads workshops in Africa and Antarctica for Muench Workshops and develops equipment for camera trap photography through his company Camtraptions. You can follow @willbl and @muenchworkshops on Instagram.

Please consider joining Will, 9 other Muench Workshop PRO photographers and a team of 8 Expedition Leaders & Naturalists in the Falklands, South Georgia, and Antarctica in October of 2020! Its going to be an EPIC expedition!