The White Paper - Exposure

Chapter 3 - Exposure

To get a quality photo, you need to get the right amount of light into the camera (aperture) for the right duration of time (shutter speed) to capture your shot realistically.

A good "quality" photo is one in which:

The subject is clear - neither too dark nor too bright
Color is distributed evenly and realistically
There is neither too little contrast (washed out) nor too much contrast(harsh highlights and shadows)
Midtones (skin, water) are realistic and rich
There are no blown highlights. No white skies, nor shining bald heads!
There is sufficient shadow detail. Even dark bushes should have leaves.

The attributes listed above refer to "technically" good pictures, not necessarily esthetically good pictures. There is, of course, much more to a great photo including subject, lighting, composition, focus, etc.

But the list above is not just a pretty good description of good quality photos, it's also an excellent description of good exposure. It is exposure, more than anything else, that determines the quality, color, noise, contrast and impact of your photos.

Underexposed Image

Overexposed Image

Correct Exposure

Exposure is determined by two factors: the amount of light coming into your camera, and how long that light shines on your sensor. The amount of light is controlled by the aperture setting of your lens. The time that the sensor is "exposed" to the light is determined by your shutter speed.

f/stop And Shutter Speed Confusion

Many new camera users are confused by the numbers used to set and describe aperture and shutter speed. With good reason.

Aperture (the opening of your lens) is defined in terms of "f/stops".

Shutter Speed (how long the shutter stays open) is defined in seconds, and more often, fractions of a second.

What confuses people is that f/stop represents the inverse of what it really means and shutter speeds can be fractions of a second or full seconds. You have to know how to interpret both.

Interpreting Aperture:

A lower f/stop brings in more light, a higher f/stop brings in less light

f2.8 brings in more light than f8

f2.8 is said to be "brighter" or "wider" than f8

Interpreting Shutter Speed

In a fractional shutter speed, the higher the denominator the lower the duration of light in a camera. The less light the shutter allows in, the "faster" the shutter is. The more light the shutter allows in, the "slower" the shutter is:

1/250th second is a five-times shorter duration than 1/50th

1/250th is said to be "faster" than 1/50th

1/40th is said to be a "slow" shutter speed.

1/1000th is said to be an "extremely fast" shutter speed

In full-seconds shutter speeds, the higher the number, the longer the duration of light in the camera:

1 second is 250 times slower than 1/250th. It will let light into your sensor 250 times longer.

Reading Shutter Speed

Reading shutter speed in your H-Series display can be very confusing. The numerator (the top number of a fractional shutter speed) is omitted.

Therefore, "40" on your shutter speed display is actually 1/40th of a second

So how do you tell the difference between 1/2 second and 2 seconds if the numerator is hidden? Sony uses the double-quotes (") to indicate full seconds.

If you see 2 on your shutter display, that represents 1/2 second.
If you see 2" on your shutter display, that represent 2 seconds.

Balancing Aperture And Shutter Speed

Aperture and shutter speed are inversely proportional. You can get the exact same exposure by admitting lots of light for a short time that you can get admitting little light for a long time. Thus, you have lots and lots of choices you can use to get a well-exposed image.

The following aperture/shutter combinations result in the same exposure:

f4 at 1/250th

f5.6 at 1/125th

f4.5 at 1/150th

Theoretically, any appropriate combination will do. That's what Program Mode is on the H-Series cameras - various combinations of aperture and shutter speeds that add up to the same exposure.

But there is a fly in the ointment. Using different apertures and shutter speeds can result in different esthetic effects. These effects can vary from blurred backgrounds to noisy images. So we often want to set one or the other to an ideal value to get the picture we want. Then we adjust the other value to continue to ensure good exposure. More on this later.

Dynamic Range

Each camera has a limit as to how many different levels of light it can see at the same time. Your camera cannot see all the brights and darks that your eyes can. You can capture either the person in front of the sun or the sun behind the person, but not both.

In any of the H-Series automatic modes, the camera will attempt to correctly control the light coming into the camera and the duration during with the sensor is exposed to the light. But due to the limits of the camera's dynamic range, it often cannot. Sony's engineers understand this and provide an assortment of exposure modes and meters to help you make the best exposure choices and implement them effectively.

Tip: The H5 and H7 provide Face Detection in the Automatic mode. This is designed exactly for the kind of shooting conditions described in this section. The camera will find the faces and expose them correctly regardless of the brightness (or dimness) of the background. At first blush, many thought this was a trivial feature. It's not.

Auto Mode

In Auto mode, an engineer has already determined "perfect exposure" based on the camera's average reading of the entire frame, and you have little say in the matter. Considering that Auto mode has to accommodate everything from beach scenes to night shooting, it's a miracle it ever gets exposure exactly right. In fact, it often doesn't.

Program Mode

Program Mode gives you a "list" to choose from of different aperture and shutter settings, all of which should give you the same exposure.

Priority Modes

Aperture and Shutter Priority modes allow you to change either the amount of light or the duration of light entering the camera. You set one, the camera sets the other.

Manual mode

In Manual mode, you determine the amount of light and the duration of the light that enters the camera by setting the aperture and the shutter speed yourself.

Manual mode gives you enormous control over the final image. But it's also more labor-intensive, and takes some time and practice to master. Take the time. The rewards, in terms of better photos and fewer failures, are well worth it.

ISO

Only aperture and shutter determine how much light gets into your camera and for how long. But there is an additional setting that can be applied after the light is captured by your camera's sensor. That's ISO.

ISO is important, particularly in low-light conditions. Your lens has a limit on how wide it can open to gather light. In the H-Series cameras, that limit changes as you zoom. You get more light (f/2.8) at wide-angle and less light (f/3.7) at full telephoto (.f/2.7 to f/4.5 in the H7 and H9).

Your shutter also has a limit as to how long it can stay open without blur and noise. CCDs have a particular problem with long-exposures. Internal temperature shifts over time can generate terrible noise in low-light pictures.

Sometimes, you're at the practical limits of the camera and still can't get enough light inside long enough to get a good exposure.

So what option do you have to get correct exposure? Raise the ISO. If you can't bring in more light, the only thing left is to amplify the light that's already come in. Not the light exactly, but the output from the sensor that gathered the light.

This is a problem. In audio, when you amplify a noisy tape, you get more noticeable noise. Crank up the volume on a cheap cassette tape, and the hiss becomes unbearable. You get more noise than music.

It's the same with digicams. When you consider that the only reason you need to amplify the sensor's output is because the sensor didn't get enough light to begin with, you realize you're not starting out in a really good place! Some of the photosites won't respond because the light was too low. Some won't be able to decide if they're supposed to be on or off or at what value. This is noise.

Amplifying the sensor's output amplifies the noise. Not to mention whatever noise is added by the electronic amplification itself! You can reduce the noise with camera-based noise-reduction, but you lose detail in a messy compromise.

Rule Of Thumb

Use the lowest ISO you can to get the picture you want. Always. If you have to, bump it up from 64 (80 on the H7 and H9) to 100, or even to 200. ISO 400 is another matter. If it is the only way to get the shot, use it. Anything above that is a real compromise requiring significant post-processing to produce a printable picture.

Noise lurks in shadows. At almost any ISO, if your setting results in a well-exposed image, you'll get little noise. Even at ISO 400. If, on the other hand, your image is seriously under-exposed, you can even get noise at ISO 100.

Summary

Exposure is getting the right amount of light to get the picture you want, by getting enough light into the camera for long enough.

You have two mechanisms to control the light: shutter speed and aperture size.

You have one mechanism for correcting underexposure after the light enters the camera: ISO.

Next: Chapter 4 - Aperture Vs. Shutter Speed
Return to White Paper Introduction and Contents



	Chapter 3 - Exposure

	To get a quality photo, you need to get the right amount of light into the camera (aperture) for the right duration of time (shutter speed) to capture your shot realistically. A good "quality" photo is one in which: The subject is clear - neither too dark nor too bright Color is distributed evenly and realistically There is neither too little contrast (washed out) nor too much contrast(harsh highlights and shadows) Midtones (skin, water) are realistic and rich There are no blown highlights. No white skies, nor shining bald heads! There is sufficient shadow detail. Even dark bushes should have leaves. The attributes listed above refer to "technically" good pictures, not necessarily esthetically good pictures. There is, of course, much more to a great photo including subject, lighting, composition, focus, etc. But the list above is not just a pretty good description of good quality photos, it's also an excellent description of good exposure. It is exposure, more than anything else, that determines the quality, color, noise, contrast and impact of your photos. Underexposed Image Overexposed Image Correct Exposure Exposure is determined by two factors: the amount of light coming into your camera, and how long that light shines on your sensor. The amount of light is controlled by the aperture setting of your lens. The time that the sensor is "exposed" to the light is determined by your shutter speed. f/stop And Shutter Speed Confusion Many new camera users are confused by the numbers used to set and describe aperture and shutter speed. With good reason. Aperture (the opening of your lens) is defined in terms of "f/stops". Shutter Speed (how long the shutter stays open) is defined in seconds, and more often, fractions of a second. What confuses people is that f/stop represents the inverse of what it really means and shutter speeds can be fractions of a second or full seconds. You have to know how to interpret both. Interpreting Aperture: A lower f/stop brings in more light, a higher f/stop brings in less light f2.8 brings in more light than f8 f2.8 is said to be "brighter" or "wider" than f8 Interpreting Shutter Speed In a fractional shutter speed, the higher the denominator the lower the duration of light in a camera. The less light the shutter allows in, the "faster" the shutter is. The more light the shutter allows in, the "slower" the shutter is: 1/250th second is a five-times shorter duration than 1/50th 1/250th is said to be "faster" than 1/50th 1/40th is said to be a "slow" shutter speed. 1/1000th is said to be an "extremely fast" shutter speed In full-seconds shutter speeds, the higher the number, the longer the duration of light in the camera: 1 second is 250 times slower than 1/250th. It will let light into your sensor 250 times longer. Reading Shutter Speed Reading shutter speed in your H-Series display can be very confusing. The numerator (the top number of a fractional shutter speed) is omitted. Therefore, "40" on your shutter speed display is actually 1/40th of a second So how do you tell the difference between 1/2 second and 2 seconds if the numerator is hidden? Sony uses the double-quotes (") to indicate full seconds. If you see 2 on your shutter display, that represents 1/2 second. If you see 2" on your shutter display, that represent 2 seconds. Balancing Aperture And Shutter Speed Aperture and shutter speed are inversely proportional. You can get the exact same exposure by admitting lots of light for a short time that you can get admitting little light for a long time. Thus, you have lots and lots of choices you can use to get a well-exposed image. The following aperture/shutter combinations result in the same exposure: f4 at 1/250th f5.6 at 1/125th f4.5 at 1/150th Theoretically, any appropriate combination will do. That's what Program Mode is on the H-Series cameras - various combinations of aperture and shutter speeds that add up to the same exposure. But there is a fly in the ointment. Using different apertures and shutter speeds can result in different esthetic effects. These effects can vary from blurred backgrounds to noisy images. So we often want to set one or the other to an ideal value to get the picture we want. Then we adjust the other value to continue to ensure good exposure. More on this later. Dynamic Range Each camera has a limit as to how many different levels of light it can see at the same time. Your camera cannot see all the brights and darks that your eyes can. You can capture either the person in front of the sun or the sun behind the person, but not both. In any of the H-Series automatic modes, the camera will attempt to correctly control the light coming into the camera and the duration during with the sensor is exposed to the light. But due to the limits of the camera's dynamic range, it often cannot. Sony's engineers understand this and provide an assortment of exposure modes and meters to help you make the best exposure choices and implement them effectively. Tip: The H5 and H7 provide Face Detection in the Automatic mode. This is designed exactly for the kind of shooting conditions described in this section. The camera will find the faces and expose them correctly regardless of the brightness (or dimness) of the background. At first blush, many thought this was a trivial feature. It's not. Auto Mode In Auto mode, an engineer has already determined "perfect exposure" based on the camera's average reading of the entire frame, and you have little say in the matter. Considering that Auto mode has to accommodate everything from beach scenes to night shooting, it's a miracle it ever gets exposure exactly right. In fact, it often doesn't. Program Mode Program Mode gives you a "list" to choose from of different aperture and shutter settings, all of which should give you the same exposure. Priority Modes Aperture and Shutter Priority modes allow you to change either the amount of light or the duration of light entering the camera. You set one, the camera sets the other. Manual mode In Manual mode, you determine the amount of light and the duration of the light that enters the camera by setting the aperture and the shutter speed yourself. Manual mode gives you enormous control over the final image. But it's also more labor-intensive, and takes some time and practice to master. Take the time. The rewards, in terms of better photos and fewer failures, are well worth it. ISO Only aperture and shutter determine how much light gets into your camera and for how long. But there is an additional setting that can be applied after the light is captured by your camera's sensor. That's ISO. ISO is important, particularly in low-light conditions. Your lens has a limit on how wide it can open to gather light. In the H-Series cameras, that limit changes as you zoom. You get more light (f/2.8) at wide-angle and less light (f/3.7) at full telephoto (.f/2.7 to f/4.5 in the H7 and H9). Your shutter also has a limit as to how long it can stay open without blur and noise. CCDs have a particular problem with long-exposures. Internal temperature shifts over time can generate terrible noise in low-light pictures. Sometimes, you're at the practical limits of the camera and still can't get enough light inside long enough to get a good exposure. So what option do you have to get correct exposure? Raise the ISO. If you can't bring in more light, the only thing left is to amplify the light that's already come in. Not the light exactly, but the output from the sensor that gathered the light. This is a problem. In audio, when you amplify a noisy tape, you get more noticeable noise. Crank up the volume on a cheap cassette tape, and the hiss becomes unbearable. You get more noise than music. It's the same with digicams. When you consider that the only reason you need to amplify the sensor's output is because the sensor didn't get enough light to begin with, you realize you're not starting out in a really good place! Some of the photosites won't respond because the light was too low. Some won't be able to decide if they're supposed to be on or off or at what value. This is noise. Amplifying the sensor's output amplifies the noise. Not to mention whatever noise is added by the electronic amplification itself! You can reduce the noise with camera-based noise-reduction, but you lose detail in a messy compromise. Rule Of Thumb Use the lowest ISO you can to get the picture you want. Always. If you have to, bump it up from 64 (80 on the H7 and H9) to 100, or even to 200. ISO 400 is another matter. If it is the only way to get the shot, use it. Anything above that is a real compromise requiring significant post-processing to produce a printable picture. Noise lurks in shadows. At almost any ISO, if your setting results in a well-exposed image, you'll get little noise. Even at ISO 400. If, on the other hand, your image is seriously under-exposed, you can even get noise at ISO 100. Summary Exposure is getting the right amount of light to get the picture you want, by getting enough light into the camera for long enough. You have two mechanisms to control the light: shutter speed and aperture size. You have one mechanism for correcting underexposure after the light enters the camera: ISO. Next: Chapter 4 - Aperture Vs. Shutter Speed Return to White Paper Introduction and Contents