# Focal length and aperture relationship questions

### f-number - Wikipedia

Motley Fool issues rare "double down" buy alert. If you increase the ISO you can have a smaller aperture and shorter shutter time, What is the relation between focal length and radius of curvature in case of a mirror having large aperture?. How does the focal length and aperture affect the exposure of the image questions and more, we will examine a model of how a lens-camera. Pop quiz: Which aperture is larger — f/8 or f/22? When you substitute focal length into the fraction, you're solving for the diameter of the aperture blades in your.

Some of the light coming from the object head toward the lens. The rays are refracted by the lens depending on where it hit the surface and at what angle. In an ideal lens, two rules determine how the rays are bent: A ray that intersects the center of the lens proceeds unchanged, and all rays emanating from one point of the object will steer toward one point on the focal plane which is where the sensor is placed.

In the diagrams on this page, the diameter is the height of the lens. For example, the diameter of a lens might be 36 mm. We will assume that all lenses are circular.

For an ideal lens, the rate of light entering the lens equals the rate of light exiting the lens. This principle will be important shortly. An aperture is not a part of the simplified lens model here, but many real lenses in have apertures. It is a variable-sized disc within the lens assembly that blocks light from the outer parts of the lens, effectively making the lens behave like a smaller one.

For our purposes, we will assume that the aperture is fully open blocking nothingso we can refer to the lens size and the aperture size interchangeably to mean the same thing. Focal lengths The focal length of a lens is a property of a lens itself unrelated to the scenedetermined by the curvature of its surfaces and the refractive index of its material. It is defined as the distance where parallel rays from an object infinitely far away converge to a single point.

Lenses with longer focal lengths produce a larger image for the same object at the same distance. For objects that are sufficiently far away, the size of the image is approximately proportional to the focal length. For example, a mm lens will produce an image that is twice as large as compared to a 50 mm lens.

However, the law of conservation of energy comes into play here. The amount of light gathered by a lens is proportional to its area. If the outgoing projected image is enlarged, then the image must be dimmer at each point because the total energy of the image must remain the same. This situation is analogous to moving a lamp farther from a wall or moving a video projector farther from the screen, both of which make the lit surface dimmer.

## f stop and crop sensors

Therefore, if two lenses have the same aperture diameter but different focal lengths, then the longer focal length lens will produce a dimmer image. Consequently, all the attention is directed to the eye, which is placed right in the center of the image.

The forest brings so many fantastic opportunities to shoot portraits. Take advantage of it! What else can you ask for? In wildlife photography, you must focus very precisely because long focal lengths produce a very shallow depth of field.

## How Do Object Distance and Focal Length Affect Depth of Field?

The photo was taken from inside a hide. The colors and beauty of the plumage of these birds makes photography an art. I was able to close the aperture because the bee-eater was staying still, which in turn allowed me to have the whole bird in focus!

I had to widen the aperture a little bit to reduce shutter speed and, thus, freeze the bird. I was pretty lucky! In every picture, the lens was focused on the rocks to keep them in focus. By stitching 11 pictures with little depth of field, you can create a panorama where the overall depth of field is quite considerable. Using the technique of focus stacking to create beautiful panoramas is another way to control the areas of the image you want to be sharp. This method consists in creating portraits by shooting several pictures with the same depth of field using a fast telephoto lens to finally build a panorama.

As you look at it, you have the impression that the image had been taken using a wide angle lens but with little depth of field.

This photo is the result of 57 frames stitched together with the software PTGui Pro. The hardest part of the job was for Aina, my little daughter, who had to stay the whole session without moving. All of them still work perfectly well! Without a doubt, the grain from analogic cameras is unbeatable, artistically speaking. The product in the foreground is a typical spirit from Mallorca. Celebrated in Ciutadella at the end of June, it includes the popular horse races. The horses and riders run among the crowd, making it an incredibly dangerous moment for both the riders and spectators.

Here, I shaked the camera to give a sense of speed to the image. Learn more about this great festival reading " Dreaming of Sant Joan ". Both details melt together in the frame. This water snake was quietly resting in a cattle trough in a nearby oak grove. After 10 minutes of "trial and error", it allowed me to focus on its eyes and I managed take this picture.

### How Do Object Distance and Focal Length Affect Depth of Field? « Physics Soup

In this case, I was able to reach a rate of magnification of 4: Of course, these are just a few examples of depth of field practical use.

Feel free to apply it to any type of photography and situation you desire Just be as much creative as possible! Take a deep breath and dive deep. The distance between the camera and the first element that is considered to be acceptably sharp is called DoF near limit.

Similarly, the distance between the camera and the furthest element that is considered to be acceptably sharp is called DoF far limit. Notice that the limits of depth of field are not hard boundaries between sharp and unsharp since defocus is produced gradually. Depth of field is not equally distributed in front near and behind far your focus point.

Usually, the far DoF is larger than the near DoF. On the contrary, the furthest you focus the less evenly distributed.

• Understanding Depth of Field for Beginners

In similar fashion, for a given focus distance, a telephoto lens will give you a more evenly distributed DoF than a wide angle lens. Depending on the settings used for the shot, the area that is considered to be acceptably sharp in your image can go from less than a millimeter Macro Photography to kilometers, and even to infinity Landscape or Astrophotography.

This last infinite depth of field situation occurs when you focus the lens at what is called the hyperfocal distance or at any distance larger than the hyperfocal distance.

An interesting depth of field fact There is a DoF fact to which I specially want you to pay attention. Have a look at the following portrait. The viewer is lead through a visual intimate path to finally discover the deepest emotions that dwell in our women. This picture represents the beginning of a terrible disease: It immortalizes the very first moment Maria, now totally recovered, looked at her falling hair and realized that her life would turn into a real nightmare.

She was suffering but also pulling all her strength and energy to fight back the disease. At the same time I wanted the body, where her cancer was growing, completely out of focus. How did I take it? First, I used a subject distance focus distance of 4.

Then, I asked Maria to separate her hands from the body. The following picture is the illustration of how depth of field worked for me that day. The Focus plane is perpendicular to the shooting direction. Take advantage of it in a creative way. With this simple example, I also want to point out that: The right spot is where everything makes sense and where all the elements you need come together in a superb image.

The aperture is the setting that beginners typically use to control depth of field. On the contrary, the smaller the aperture large f-number: PhotoPills includes a depth of field chart and an advanced DoF calculator where you can change these hypothesis to adjust the circle of confusion you need. These two distances are the same only when you want to focus at the hyperfocal distance.

The hyperfocal distance only depends on aperture, focal length, camera sensor and circle of confusion. It does not depend on subject distance focus distance. So, subject distance is not a field you need to introduce when calculating the hyperfocal distance.

Just to make it clear, use the calculator to fill in the hyperfocal distance in the subject distance field. Use the automatic focus system of your camera to focus at the hyperfocal distance. Set back the camera to manual focus. Point and shot… that simple! Hyperfocal distance definition In other words, when the lens is focused at the hyperfocal distance, everything that falls at any given distance from half of this distance out to infinity will be acceptably sharp, which is the maximum depth of field you can have.

Notice that if you focus at a distance that is shorter than the hyperfocal distance, the depth of field far limit will not be at infinite. This will result into blurring the elements at the horizon or furthest background elements like mountains or stars. In practice, as I explain in the article " How to shoot truly contagious Milky Way pictures ", focusing exactly at the hyperfocal distance is very difficult.