Refractionformula

In order to see where depth of field begins to blur the background, look toward the upper right of the photo. There we begin to see the legs and feet of people walking past start to go out of focus. I would have preferred a smaller depth of field but this was a “let me test my manual setting really quick” shot of this boy running past me. I was so focused on getting settings nailed down that I didn’t even notice he’d fallen until I checked my screen and by then he was up and gone!

Refractionin physics

Since refraction of light occurs when it crosses the boundary, visual distortions often occur. These distortions occur when light changes medium as it travels from the object to our eyes.

Here you can see the dragonfly is in focus, but the grass behind is completely out of focus and blurry. I was close when I snapped this photo and was using my telephoto lens to allow me to get really focused in on my subject. This combination of closeness to the subject and use of a zoom lens enabled this level of background separation even though my aperture was at a mid-range setting.

Refractionexamples

You’ll quickly get the hang of it and be sharing photos that have all your friends praising your photography skills on the social media platform of your choice!

Refractioneye exam

Focal length: Greater focal length = shorter DOF. Distance to subject: Greater distance to subject = longer DOF.\ Aperture width: Wider aperture (smaller f number) = shorter DOF.

For good measure, here is another example with even greater depth of field. To capture this waterfall, I stood pretty close to the edge and shot alongside it while focusing midway across. Because I had a mid-range focal length and had my aperture opening pretty small, all the features in the photo are recognizable. You can clearly see the wall in the background and the rest of the waterfall in the foreground.

Depth of field (DOF), simply put, is the portion of your photo that is perfectly in focus. Due to the nature of camera components and the way they interact with light, every photo you take (with some random exceptions we won’t get into) will be impacted by your focal length, the distance to your subject (the object or person you are photographing) and your aperture. There are several mathematical calculations involved in determining exactly what depth of field you can expect, but as my goal is to make this subject a simple and easy to remember as possible, I’m going to forgo those explanations for today. If you have some free time and want to explore this in more depth, I’d recommend checking out an online depth of field calculator.

Refractiondiagram

From these photos you can clearly see that with minimal effort and a basic understanding of how to control just a single component of your camera, you are able to completely change the texture and appearance of your photos.

In Unit 13 of The Physics Classroom Tutorial, it was emphasized that we are able to see because light from an object can travel to our eyes. Every object that can be seen is seen only because light from that object travels to our eyes. As you look at Mary in class, you are able to see Mary because she is illuminated with light and that light reflects off of her and travels to your eye. In the process of viewing Mary, you are directing your sight along a line in the direction of Mary. If you wish to view the top of Mary's head, then you direct your sight along a line towards the top of her head. If you wish to view Mary's feet, then you direct your sight along a line towards Mary's feet. And if you wish to view the image of Mary in a mirror, then you must direct your sight along a line towards the location of Mary's image. This directing of our sight in a specific direction is sometimes referred to as the line of sight.

The size of an image sensor, whether digital or film, affects depth of field in a similar way to a lens aperture. This is because depth of field is a product of both the lens aperture and focal length, plus the sensor size relative to that aperture and focal length.

Not only is this an example of “the decisive moment,” it is an example of a larger depth of field. This is achieved by being a bit further from the subject in the photo and by having a smaller aperture opening.

Here is an example of how distance and focal length can impact your depth of field. The closer you are to your subject, the more likely you are to blur out the foreground and background of your photo. That probability increases as you increase your focal length by zooming in. I was less than two feet from Mr. Bug here (close enough for him to stare back at me) and had my lens extended all the way. Even though my aperture was set to a mid-range value of f6.3, the fore and backgrounds are pretty blurry, helping the eye focus on the subject in the center of the frame.

You’ve purchased a camera, you’re out there taking photos, and you’ve made your way to one of the premier resources for all things photography on the web, so I know you want to learn how to create eye-popping photos! With that in mind, here’s an assignment that will help you take your photo taking skills to the next level…

A small, tight, dark lens aperture lets less light into the camera, but because it is smaller, it focuses the light very sharply for a greater depth that extends in front of and behind the actual focus distance.

A large, bright lens aperture lets a lot of light into the camera and onto the image sensor, however such a big aperture also results in a very thin plane of focus, and a lot of foreground and/or background blur.

As light travels through a given medium, it travels in a straight line. However, when light passes from one medium into a second medium, the light path bends. Refraction takes place. The refraction occurs only at the boundary. Once the light has crossed the boundary between the two media, it continues to travel in a straight line. Only now, the direction of that line is different than it was in the former medium. If when sighting at an object, light from that object changes media on the way to your eye, a visual distortion is likely to occur. This visual distortion is witnessed if you look at a pencil submerged in a glass half-filled with water. As you sight through the side of the glass at the portion of the pencil located above the water's surface, light travels directly from the pencil to your eye. Since this light does not change medium, it will not refract. (Actually, there is a change of medium from air to glass and back into air. Because the glass is so thin and because the light starts and finished in air, the refraction into and out of the glass causes little deviation in the light's original direction.) As you sight at the portion of the pencil that was submerged in the water, light travels from water to air (or from water to glass to air). This light ray changes medium and subsequently undergoes refraction. As a result, the image of the pencil appears to be broken. Furthermore, the portion of the pencil that is submerged in water appears to be wider than the portion of the pencil that is not submerged. These visual distortions are explained by the refraction of light.

Refractioneye

In this case, the light rays that undergo a deviation from their original path are those that travel from the submerged portion of the pencil, through the water, across the boundary, into the air, and ultimately to the eye. At the boundary, this ray refracts. The eye-brain interaction cannot account for the refraction of light. As was emphasized in Unit 13, the brain judges the image location to be the location where light rays appear to originate from. This image location is the location where either reflected or refracted rays intersect. The eye and brain assume that light travels in a straight line and then extends all incoming rays of light backwards until they intersect. Light rays from the submerged portion of the pencil will intersect in a different location than light rays from the portion of the pencil that extends above the surface of the water. For this reason, the submerged portion of the pencil appears to be in a different location than the portion of the pencil that extends above the water. The diagram at the right shows a God's-eye view of the light path from the submerged portion of the pencil to each of your two eyes. Only the left and right extremities (edges) of the pencil are considered. The blue lines depict the path of light to your right eye and the red lines depict the path of light to your left eye. Observe that the light path has bent at the boundary. Dashed lines represent the extensions of the lines of sight backwards into the water. Observe that these extension lines intersect at a given point; the point represents the image of the left and the right edge of the pencil. Finally, observe that the image of the pencil is wider than the actual pencil. A ray model of light that considers the refraction of light at boundaries adequately explains the broken pencil observations.

The broken pencil phenomenon occurs during your everyday spearfishing outing. Fortunately for the fish, light refracts as it travels from the fish in the water to the eyes of the hunter. The refraction occurs at the water-air boundary. Due to this bending of the path of light, a fish appears to be at a location where it isn't. A visual distortion occurs. Subsequently, the hunter launches the spear at the location where the fish is thought to be and misses the fish. Of course, the fish are never concerned about such hunters; they know that light refracts at the boundary and that the location where the hunter is sighting is not the same location as the actual fish. How did the fish get so smart and learn all this? They live in schools.

Now any fish that has done his/her physics homework knows that the amount of refraction that occurs is dependent upon the angle at which the light approaches the boundary. We will investigate this aspect of refraction in great detail in Lesson 2. For now, it is sufficient to say that as the hunter with the spear sights more perpendicular to the water, the amount of refraction decreases. The most successful hunters are those who sight perpendicular to the water. And the smartest fish are those who head for the deep when they spot hunters who sight in this direction.

What isrefractionClass 10

Set your camera mode to aperture priority (“A” on Nikon, “Av” on Canon) and work on creating that nice separation from the background. Focus on the ways of doing so that we discussed today.

Refractionof light

Today, though, we’re keeping things simple and to the point. To break this somewhat complex interplay between your camera and light down into simpler concepts, remember:

Here is an example of blurred background using my prime lens. Utilizing a lower aperture and getting close to my subject helped keep the face, snow, and ice sharp, but blurred out the background details that may have distracted from the shot.