Intro exposure

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My intro primer on the basics of photographic exposure.

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Intro exposure

  1. 1. Introduction to Photographic Exposure Michael E. Stern Photographer Educator Trainer 818-422-0696 CyberStern.com 1
  2. 2. Introduction to Photographic Exposure Exposure: The combination of time, intensity, light sensitivity (ISO) of the medium and local light energy that creates an image onto light sensitive material. Time X Intensity = Exposure 2
  3. 3. Introduction to Photographic Exposure Proper Exposure: The specific combination of shutter speed (time), aperture (intensity), ISO (light sensitivity) and light energy that provides the photographer with the sought after look, effect, mood or feel. The specific exposure combination is driven by the technical and reproduction requirements of an assignment. 3
  4. 4. Introduction to Photographic Exposure Exposure is the sum of these four factors: 1) Illuminance/local light energy: The factor that you typically have no control over. For example, direct sunlight, standing in open shade, the light of a candle or the brightness during overcast conditions You can control the amount of light by adding flash, moving you and/or your subject or waiting for different weather, time of day, etc. 2) Shutter speed: Should be thought of as the time or duration and is usually measured in 1/3 stop increments. Denoted as fractions of a second: 1/2, 1/50, 1/4000 and so on. Can also be denoted in full seconds, minutes and hours. 3) Aperture/intensity: Also referred to as f/stop and is the size of the lens opening through which light passes. Usually measured in 1/3 stop increments. 4) ISO/light sensitivity: This setting controls how well the chip reacts to the combination of the other three factors. A numerical rating that describes the sensor’s sensitivity to light. Is usually measured in 1/3 stop increments. 4
  5. 5. Introduction to Photographic Exposure Exposure Basics A stop is a change in exposure or illumination by a factor of two. One stop more exposure doubles the amount of light and one stop less exposure halves the amount of light. 5
  6. 6. Introduction to Photographic Exposure Shutter Speed One of the basic tenants of photographic theory is the half as much and twice as much concept. This concept states that a one stop increase in time (slowing the shutter speed from 1/50 to 1/25) allows twice as much time for light energy to expose the image sensor. A one stop decrease (increasing the shutter speed to 1/25 to 1/50) cuts the time in half. In photography we work with stops as the foundation for changing exposure. 6
  7. 7. Introduction to Photographic Exposure Shutter Speed 1 sec 1/2 A one stop difference 1/2 A one stop difference 1/4 1/4 A one stop difference 1/8 1/8 A one stop difference 1/15 1/15 A one stop difference 1/30 1/30 A one stop difference 1/60 1/60 A one stop difference 1/125 1/125 A one stop difference 1/250 1/250 A one stop difference 1/500 7
  8. 8. Introduction to Photographic Exposure Shutter Speed Every red number is one stop away from the next red number. In between there are two intermediate stops. These are referred to as 1/3 stops. There are always two 1/3 stop choices in between each whole stop. Cameras can also be set to 1/2 stop increments. Precise control over exposure is compromised when working in 1/2 stops. When the shutter speed is 1/250 of a second and it’s then changed to 1/125 of a second, the time has been doubled (the shutter is open twice as long), increasing the exposure value by one whole stop. The photo will become lighter. If you move in the opposite direction, then you have cut the time in half (the shutter is open half as long) and have decreased the exposure by one whole stop. The photo becomes darker. 8
  9. 9. Introduction to Photographic Exposure Shutter Speed & Exposure Some examples...... From 1/8000 .....................To 1/4000 is one full stop more exposure. (1/2 the number = twice the time) 1/8000..... is twice as fast as .....1/4000 and lets in half as much light. 1/4000..... is half as fast as .....1/8000 and lets in twice as much light. Because Shutter Speeds are listed as fractions of a second they relate to one another in this “twice as much” or “half as much” way at full stop intervals. 9
  10. 10. Introduction to Photographic Exposure Shutter Speed 1/4000............... is twice as fast as ................1/2000 1/2000............... is twice as fast as ................1/1000 1/1000............... is twice as fast as ................. 1/500 1/500................. is twice as fast as ..................1/250 1/250................. is twice as fast as ..................1/125 1/125..................is twice as fast as ...................1/60 When a shutter speed is twice as fast as the previous shutter speed, half as much time is allowed for exposure. The opposite is true when the shutter speed is half the time (the fractional number) as the previous shutter speed. At this point twice as much time is allowed for light energy to travel through the lens barrel back to the image sensor. 10
  11. 11. Introduction to Photographic Exposure Aperture Scale* Controls the amount of light passing through the lens barrel. Every red number is one stop away from the next red number. In between there are two intermediate stops. These are referred to as 1/3 stops. There are always two 1/3 stop choices in between each whole stop. Cameras can also be set to 1/2 stop increments. Precise control over exposure is compromised when working in 1/2 stops. When an aperture is set to 8.0 and it’s then changed to 5.6, the intensity has been doubled (the iris is larger), increasing the exposure value by one whole stop. The photo will become lighter. If you move in the opposite direction, then you have cut the intensity in half (the iris is smaller) and have decreased the exposure by one whole stop. The photo becomes darker. *Also known as the f/stop scale 11
  12. 12. Introduction to Photographic Exposure Inside every lens is a diaphragm which controls the opening of the iris. This in turn controls the flow or intensity of light traveling through the lens barrel to the light sensitive recording media (the sensor). Question: Why does a smaller number represent a larger opening? 12
  13. 13. Introduction to Photographic Exposure F/Stop The ‘f’ number represents the amount of light and is figured by the size of the opening (aperture) divided by the focal length of the lens. 13
  14. 14. Introduction to Photographic Exposure F/Stops Due to the specifics of lens design, apertures let in the same amount of light regardless of f/stop. F/5.6 lets in the same intensity of light on a 200mm lens as a 50mm lens. This is important to remember. 14
  15. 15. Introduction to Photographic Exposure Exposure Before we discuss how ISO’s, factor into exposure control, you must appreciate that there is a reciprocal relationship between aperture and shutter speed. 1/50 @ f/8.0 = 1/100 @ f/5.6 This reciprocal relationship is the way to balance exposure. 15
  16. 16. Introduction to Photographic Exposure Exposure So How Do Shutter Speed and Aperture Work Together? The rule of thumb for proper exposure: If we choose a slower shutter speed 1/50 IRIS (lengthening the amount of time light travels through the lens barrel), then we have to choose a smaller opening to let in 1/25 IRIS less light. A larger opening in the lens is a smaller f/stop (f/4.0) number. And vice- versa. 16
  17. 17. Introduction to Photographic Exposure ISO Determines the sensitivity of film and digital chip. It is represented by a numerical value in 1/3 stop increments. Each red number is one whole stop away from the next red number. In between there are two intermediate stops. These are referred to as 1/3 stops. There are always two 1/3 stop choices in between each whole stop. Cameras can also be set to 1/2 stop increments. Precise control over exposure is compromised when working in 1/2 stops. If ISO 400 is “twice as much” as ISO 200, at ISO 400 the chip in the camera is “twice as sensitive” as the same chip at ISO 200. This same principal is applied to shutter speed and f/stops. 17
  18. 18. Introduction to Photographic Exposure ISO If ISO 400 is “twice as much” as ISO 200, at ISO 400 the chip in the camera is “twice as sensitive” as the same chip at ISO 200. It stands to reason then, that a shutter speed of 400 is twice as fast as a shutter speed of 200. With twice the chip sensitivity (and assuming the f/stop remains constant), it only requires the shutter to be open half as long to produce the exact same exposure. 18
  19. 19. Introduction to Photographic Exposure At ISO 200 Exposure = 1/200 @ f/16 19
  20. 20. Introduction to Photographic Exposure At ISO 400 Exposure = 1/400 @ f/16 20
  21. 21. Introduction to Photographic Exposure ISO 400 ISO 200 So, side by side, it’s clear to see that the exposure is the same if illumination is a constant no matter what the ISO. If we learn to understand how ISOs, shutter speeds, and f-stops relate, we will then be fluent in understanding the basics of photography. 21
  22. 22. Introduction to Photographic Exposure Exposure In the world of camera controls Half as Much and Twice as Much inherently applies in one stop increments. 22
  23. 23. Introduction to Photographic Exposure Exposure Let’s try a problem... 1/200 @ f/16 is the same as 1/? @ f/5.6 23
  24. 24. Introduction to Photographic Exposure Exposure Returning to the f/Stop scale f/2.8 f/4.0 f/5.6 f/8.0 f/11 f16 f/5.6 is 3 stops more light than f/16. Therefore, our shutter speed has to be 3 stops faster. 24
  25. 25. Introduction to Photographic Exposure Exposure On The Shutter Speed Scale 100 200 400 800 1600 Which number is 3 stops faster than 200? 25
  26. 26. Introduction to Photographic Exposure Exposure The answer: 1/200 @ f/16 is the same as 1/1600 @ f/5.6 26
  27. 27. Introduction to Photographic Exposure Equivalent Exposures 1/1600 @ f/5.6 Equivalent Exposures 1/200 @ f/16 27
  28. 28. Introduction to Photographic Exposure Equivalent Exposures As one camera control changes, either shutter speed or f/stop, the other camera control must move in an equal but opposite direction to maintain a balance to the exposure. This concept is called equivalent exposures. Example to follow. 28
  29. 29. Introduction to Photographic Exposure Equivalent Exposures In addition to earlier illustrating the concept of Depth of Field, these two images also demonstrate the concept of Equivalent Exposure. Equivalent exposure refers to maintaining the same exposure value despite changing camera controls. As one camera control moves (shutter speed), the other camera control (f/stop) moves in an equal but opposite direction. -or- To maintain equivalent exposures, when we increase our shutter speed we must also decrease our f- stop (aperture) by the same amount. Conversely, if we decrease our shutter speed we must then increase our f-stop 1/60 @ f/5.6 ISO 200 (aperture) by the same amount. .6 sec @ f/36 ISO 200 ������������������������������������������������������������������������������������ ��������������������������������������������������������������������������������� ����������������������������������������������������������������������� 29
  30. 30. Introduction to Photographic Exposure Michael E. Stern Photographer Educator Trainer 818-422-0696 CyberStern.com 30

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