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Basic photography concepts I aperture I shutter speed I ISO speed I exposure

Basic photography concepts: aperture, shutter speed, ISO speed, exposure

Basic photography concepts: aperture, shutter speed, ISO speed, exposure


Photography is all light. Let the camera "see" your will, you have the tools to control how much light the camera sensor has reached: aperture and shutter speed controls. With very little light, your image will be very dark. With too much light, it will be too bright. In both cases, some details will be lost. If you use aperture and shutter speed to achieve the correct exposure, you should be aware of some important side-effects when taking into consideration.

Imagine that you are looking through a small round hole in a fence. How much can you see and understand behind the fence? I would say it depends on two factors:


  1. How large the hole is . The larger it is, the more you can see.
  2. How long do you look The more you look, the more details you notice.

The same story happens in a photo camera. I'm now at risk of getting a negative evaluation of my physics knowledge, which unfortunately will be fair enough ... but even though the physical factors are different, the conceptual comparison seems to be quite sufficient. When shooting with a photo camera, the sensor allows the view through a hole in the lens called the aperture the The larger the hole, the more light it reaches the sensor. Usually the sensor is turned off by a screen called a shutter. When shooting, the shutter opens, the light through the aperture hole reaches the sensor and then it closes again. The longer the opening is, the more light reaches the sensor. This time is called shutter speed.


When shooting, your goal is to expose the right amount of light to the camera's sensor (that's why it's called exposure). If you provide enough light, the photo will be very dark. If you light too much the photo will be very bright. The higher the deviation from normal exposure, the more likely you are to lose your image data optimistically. Software post-processing can fix the perceived exposure (for example a darker image looks brighter) but it cannot reproduce lost image data during shooting. For example, one very common landscape photography problem is losing clouds in a bright sky. When it is illuminated (excessive light reaches the sensor) the entire sky becomes completely white and the cloud can no longer be separated. On the other hand, with the invisible (very little light reaches the sensor), the shaded parts of the image are lost in detail, completely black. The software cannot retrieve such details, since they are not in the original image.

When shooting, your goal is to expose the right amount of light to the camera's sensor (that's why it's called exposure). If you provide enough light, the photo will be very dark. If you light too much the photo will be very bright. The higher the deviation from normal exposure, the more likely you are to lose your image data optimistically. Software post-processing can fix the perceived exposure (for example a darker image looks brighter) but it cannot reproduce lost image data during shooting. For example, one very common landscape photography problem is losing clouds in a bright sky. When it is illuminated (excessive light reaches the sensor) the entire sky becomes completely white and the cloud can no longer be separated. On the other hand, with the invisible (very little light reaches the sensor), the shaded parts of the image are lost in detail, completely black. The software cannot retrieve such details, since they are not in the original image.

So, it is very important to get the exposure during shooting. But what is "right"? Does this mean "the image should look as dark / dark as I want to put in the final photograph"? No! By "right" I mean that the exposure must be such that the maximum number of scenes in detail is captured by the sensor. Record as much visual information as possible - this is for the camera! Then you present this information to your liking, see also the final photograph (why software post-processing is required) in Photo Sense. In fact, properly lit photos often look awful dull before software post processing.

Fortunately modern photo cameras often provide accurate automatic exposure assessment. At least with a natural, under-the-even light, their evaluation is usually great. In automatic mode, the camera recommends using aperture and shutter speed values. They guarantee a good exposure. But are these the best possible values? Why not make the aperture hole twice the shutter speed by half? The amount of time it takes to reach the sensor will be the same, thus there is no difference, right? Well, in reality it does. Although the exposure is still the same (and correct), this change can make a great difference in the resulting photograph. Both the aperture and the shutter speed affect more aspects than how much light reaches the sensor, and a photographer must always keep them in mind to get the best results. Even though your camera is good, it is still unable to read your mind and thus know exactly what you want. Let’s look at aperture and shutter speed in more detail and discuss their important side effects.

Aperture and depth of field
As stated above, aperture defines how large the hole through which the sensor looks at the world. Aperture in photography is measured at F-numbers, F-stops or anything else with this F. Without going into the details of what this F-actually is (I should look for it myself to explain physics again), below is what you really need to know. The smaller the F number, the larger the aperture hole and the more light the sensor reaches. From now on I mean "large aperture" by a larger aperture hole (and a smaller F number) and vice versa "smaller aperture".

In practice, depending on the lens you have, you use the F-value from approximately F4 (large aperture) to about F16 (small aperture). Some quality lenses support larger apertures, for example my favorite Nikon lenses (85mm and 50mm) go to F1.8 or even F1.4. These very light sensitive lenses keep you in the dark (more about lenses and low-light photography).

In addition to the amount of sensor reach, aperture affects one more important aspect: depth of field. Imagine a number of objects located at different distances from the camera. Say a person 5 meters away, a bear 7 meters away and a tree 10 meters away. The camera shows them all, but the question is: What things are in focus? The greater the depth of field, the more objects are in focus. And the smaller the aperture (the larger the F number), the greater the depth of field. So, just to get the person in focus (out of focus with bears and trees), focus on the person and set the maximum aperture, such as F1.8. This is great for portraits with beautiful opaque backgrounds. To capture the whole scene, you also want to keep the bear and the tree in focus - use a larger F-number such as F8 or higher.

Note that aperture is not the only parameter affecting depth of field. For example, the distance between the photographer and the subject also plays a very important role. The closer you get to the first topic, the smaller the depth of field is.


Shutter speed
Shutter Speed ​​Time When the shutter screen is open, the sensor illuminates. Don't worry, there are no scary F-numbers here :-). The shutter speed is measured in ordinary seconds. In bright daylight, we typically use one-hundredth of a second. It may be a tenth of a second when cloudy, in the shade, etc. At night it comes in full seconds.

The shutter records everything the sensor has seen while it's open. It does not realize what the objects are, it divides the view into several million dots and records the color of each point during exposure. Imagine that it's pretty dark, and we're shooting a moving vehicle at shutter speeds of 1 second. At a speed of just 50 kilometers per hour, the car will accelerate to about 14 meters at this time. The sensor will see the car in its initial position for the first time. Then the car will move to a location where the sensor had previously only seen the background and the sensor will now see only the background at the initial position of the car and hence the final car position. What happens in the picture of the result? A 14 meter long semi transparent car! :-)

The car we got is not sharp, it says speed bumps. Motion ambiguity is the result of shooting moving objects with long shutter speeds. This is a side effect of the shutter speed that you should always keep in mind. If you want to get a sharp object, make sure the shutter speed is fast enough to freeze its speed. If you want to get a motion-blinking object to emphasize speed, make sure the shutter speed is slow enough.

ISO Speed ​​(sensitivity)
When you can't get the right exposure with aperture and shutter speed, it's time to think about ISO sensitivity (also called ISO speed). It defines how sensitive the camera sensor is to illumination. With the same amount of light available, the higher the ISO sensitivity, the more likely the sensor will be captured by the sensor.

ISO sensitivity is measured ... in numbers! :-) I don't know exactly what these numbers are, I never needed them (now, I'm curious as I write this :-)). The "normal" ISO speed depends on your camera. In my experience it is either ISO 100 or ISO 200 you this is what you start with. If you can't get the right exposure by changing the aperture and shutter speed, try adjusting the ISO speed. I can't remember a situation when I needed to slow down my normal ISO speed. Aperture and shutter speed can reduce the amount of light required in most cases, with the rare exception. There are other ways to reduce the amount of light, such as lens filters. ISO sensitivity control is generally useful with insufficient light. When ISO 100 is not enough, try ISO 200, ISO 400 etc.

This, however, is not so easy. Aperture and shutter speed controls can be considered as safe, as they are a natural measure: change the amount of light. ISO sensitivity is more artificial, it comes at a price. The more sensitive the sensor is, the more the image sounds. The quality of the equipment becomes important when it comes to photography: Expensive professional cameras usually allow for much higher ISO speeds before the noise of the image is preventable. I never shot above ISO 800 with my entry-level DSLR Nikon D80

Find the Right Balance!
You as a photographer decide the correct exposure configuration. Modern cameras in automatic mode provide you with a (usually good) resolution: the combination of an aperture and shutter speed achieves accurate exposure. You evaluate this combination depending on your goals. Does it achieve the desired depth of field? Is the shutter speed fast enough to avoid motion blurring, or is it slow enough to make it? Adjust if necessary. For example, increase the depth of field, lower the aperture and increase the shutter speed (or ISO sensitivity). See more tips and examples in the Basic Photo Shooting Guide.

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