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Exposure Q, FAQ
Hi,.

I have few queries regarding Exposure..

1. Is it a function of F-stop & shutter speed?.

2. Is there any relation of exposure with ISO.

3. When camera detects less exposure, what it does?.

4a. If I am in portrait mode and there is less light, what it will do..

4b, if the scene is very bright, what it will do?.

5. If I increase the exposure compensation in P, A, M, S mode, what it will do.

6. any example of using ISO (increase and decrease).

SG..

Comments (11)

I have a few answers... .

Sudipta Ghosh wrote:.

Hi,.

I have few queries regarding Exposure..

1. Is it a function of F-stop & shutter speed?.

2. Is there any relation of exposure with ISO.

Exposure is a function of 3 things: lens aperture, exposure time, and sensitivity of the sensor/film..

3. When camera detects less exposure, what it does?.

It depends on what exposure mode you have selected. In M, it does nothing. In P, it changes any of the parameters, depending on it's internal algorithms and your inputs. In S and A modes, it "locks" one of the parameters to a value you select..

4a. If I am in portrait mode and there is less light, what it will do..

I don't know what "portrait" mode is. Well, I do, but let's play like I don't....

4b, if the scene is very bright, what it will do?.

Adjust something, unless you tolld it not to. It's just a tool in YOUR hands..

5. If I increase the exposure compensation in P, A, M, S mode, whatit will do.

Change the sensitivity (usually)..

6. any example of using ISO (increase and decrease).

Some cameras have modes where the sensitivity can be changed automatically by the camera. Normally, there are upper and lower limits..

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/'Experience: Discovering that a claw hammer will bend nails.Epiphany: Discovering that a claw hammer is two tools...'..

Comment #1

A quibble with Charlie's otherwise excellent reply..

Re> > 5. If I increase the exposure compensation in P, A, M, S mode, whatit will do.

Change the sensitivity (usually)..

But I say.** Depends on the camera. With most digital single lens reflex cameras, the shutter speed will change if you have selected aperture priority (to modify overall exposure while maintaining the aperture you want) If you've selected shutter priority, the aperture will change. With program, a bit of change with both aperture and shutter speed...

Comment #2

Sudipta Ghosh wrote:.

Hi,.

I have few queries regarding Exposure..

1. Is it a function of F-stop & shutter speed?.

Yes - both control how much light enters the camera.

2. Is there any relation of exposure with ISO.

Yes - ISO controls the sensitivity or effect of light on the sensor (It does not change how much light enters the camera.)http://www.dpreview.com/learn/?/Glossary/Exposure/Exposure_01.htm.

3. When camera detects less exposure, what it does?.

The possibilities would include changing ISO, aperture, shutter speed or flash..

4a. If I am in portrait mode and there is less light, what it will do..

4b, if the scene is very bright, what it will do?.

5. If I increase the exposure compensation in P, A, M, S mode, whatit will do.

6. any example of using ISO (increase and decrease).

Http://www.dpreview.com/reviews/nikond40x/page17.asp.

SG..

Comment #3

Sudipta Ghosh wrote:.

3. When camera detects less exposure, what it does?.

This seems like a badly phrased question. The camera has a *light meter*, which measures light. It adjusts F-stop, shutter speed and ISO so that the exposure is 'correct' as determined by it's computer algorithms..

4a. If I am in portrait mode and there is less light, what it will do..

4b, if the scene is very bright, what it will do?.

5. If I increase the exposure compensation in P, A, M, S mode, whatit will do.

6. any example of using ISO (increase and decrease).

Low lighting situations, indoor = use high ISO (e.g. 800)outdoor, sunny day = use low ISO (e.g. 200).

I had the same questions as you. I realized, however that the dslr is more than a camera.. so much more: Sophisticated light meter, image processor/analyzer, photosensor/detector system. It's like a micro-photo-laboratory..

All of the questions can be answered with some very simple experimentation. I'm finding it's the most fun way to learn...

Comment #4

Terminology seems to be changing with digital, but sensitivity (ISO) has not in the past been considered to be part of "exposure"..

"Exposure" is the controlling of the amount of light that falls on the film or sensor. At a given sensitivity (ISO), there is a particular exposure that will give the desired results..

Without flash, exposure is controlled by the f-stop and the exposure time (shutter speed)..

For on-camera single-burst flash photography, exposure is controlled by f-stop, flash strength, flash burst duration, and subject distance& as well as the ambient lighting exposure via f-stop and exposure time. For on-camera High Speed (FP) Sync flash photography, exposure is controlled by f-stop, exposure time, flash strength, flash microburst duration, and subject distance. With off-camera flash systemsespecially with multiple unitsthe process gets more complicated..

(I specifically used the term "f-stop" above because it combines both aperture and focal length. As photographers we basically just care about the f-stop, not the actual aperture.).

(The above is for still photography. Different controls apply to movie and video photography.).

Changing the sensitivity (ISO) will change what the correct exposure settings would be for a desired result..

These days, many people use the term "exposure" more loosely to refer to the brightness of the captured image. With that usage, sensitivity (ISO) is also included as part of "exposure"...

Comment #5

Doug Pardee wrote:.

Terminology seems to be changing with digital, but sensitivity (ISO)has not in the past been considered to be part of "exposure"..

"Exposure" is the controlling of the amount of light that falls onthe film or sensor. At a given sensitivity (ISO), there is aparticular exposure that will give the desired results..

Without flash, exposure is controlled by the f-stop and the exposuretime (shutter speed)..

For on-camera single-burst flash photography, exposure is controlledby f-stop, flash strength, flash burst duration, and subjectdistance& as well as the ambient lighting exposure via f-stop andexposure time. For on-camera High Speed (FP) Sync flash photography,exposure is controlled by f-stop, exposure time, flash strength,flash microburst duration, and subject distance. With off-cameraflash systemsespecially with multiple unitsthe process gets morecomplicated..

(I specifically used the term "f-stop" above because it combines bothaperture and focal length. As photographers we basically just careabout the f-stop, not the actual aperture.).

(The above is for still photography. Different controls apply tomovie and video photography.).

Changing the sensitivity (ISO) will change what the correct exposuresettings would be for a desired result..

These days, many people use the term "exposure" more loosely to referto the brightness of the captured image. With that usage, sensitivity(ISO) is also included as part of "exposure"..

I *really* and truly appreciate your answer here Doug. I, too, am of the opinion that ISO is not an 'exposure parameter', rather it changes the sensitivity of the light sensors. Lemme guess - are you an engineer?.

The anal part of me thinks that exposure should be reserved for describing the amount of light that reaches the sensor (which includes, flash, shutter speed, aperture)..

Are there any fancier words (perhaps more precise) used to describe brightness?..

Comment #6

I think the best way to get you jump started on learning about exposure is grasping the concept of "Zones" or Zone System..

Http://www.luminous-landscape.com/tutorials/zone_system.shtml.

It's still relevant because that's what the light or EV meter is doing on the modern cameras today: 0.0 is Middle Gray, or Zone 5.'OOOOOH, they have the Internet on computers now!' Homer J. Simpson..

Comment #7

Photoeng wrote:.

Doug Pardee wrote:.

Terminology seems to be changing with digital, but sensitivity (ISO)has not in the past been considered to be part of "exposure"..

"Exposure" is the controlling of the amount of light that falls onthe film or sensor. At a given sensitivity (ISO), there is aparticular exposure that will give the desired results..

I *really* and truly appreciate your answer here Doug. I, too, am ofthe opinion that ISO is not an 'exposure parameter', rather itchanges the sensitivity of the light sensors. Lemme guess - are youan engineer?.

I guess I'm the "odd man out" here?.

I agree with Doug that with the digital photography revolution a new paradigm is needed. If we consider ONLY the photons that reach the sensor, then sensitivity is not included in "exposure". But if we consider the charge (signal) that reaches the ADC, then sensitivity IS a part of "exposure"..

The anal part of me thinks that exposure should be reserved fordescribing the amount of light that reaches the sensor (whichincludes, flash, shutter speed, aperture)..

You probably need to use "anal retentive" or "AR" to describe the above tendency? .

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/'Experience: Discovering that a claw hammer will bend nails.Epiphany: Discovering that a claw hammer is two tools...'..

Comment #8

Chuxter wrote:.

Photoeng wrote:.

The anal part of me thinks that exposure should be reserved fordescribing the amount of light that reaches the sensor (whichincludes, flash, shutter speed, aperture)..

You probably need to use "anal retentive" or "AR" to describe theabove tendency? ..

Comment #9

Photoeng wrote:.

Are there any fancier words (perhaps more precise) used to describebrightness?.

You are referring to "Light Value" or LV. However, most use the term "Exposure Value" (EV) to refer to LV..

LV = ISO, shutterspeed, f-stopEV = shutterspeed, f-stop.

See link:http://www.dpreview.com/learn/?/Glossary/Exposure/Exposure_01.htmHope this helps...

Comment #10

Sudipta Ghosh wrote:.

I have few queries regarding Exposure..

1. Is it a function of F-stop & shutter speed?.

Yes..

2. Is there any relation of exposure with ISO.

ISO determines the "sensitivity" of the film/sensor (on digital, it increases the gain). It is linked to exposure..

3. When camera detects less exposure, what it does?.

It depends on what mode you are in. But when the camera's light meter detects low light levels, it will try to do any combination of the following: slower shutter speed, larger aperture, higher ISO, flash..

4a. If I am in portrait mode and there is less light, what it will do..

Don't know. It depends on the camera..

4b, if the scene is very bright, what it will do?.

It depends on what mode you are in. But when the camera's light meter detects higher light levels, it will try to do any combination of the following: faster shutter speed, smaller aperture, lower ISO..

5. If I increase the exposure compensation in P, A, M, S mode, whatit will do.

In P, A, and S mode, it will make the picture brighter by changing shutterspeed or f-stop (or both). In M mode, nothing..

6. any example of using ISO (increase and decrease).

I don't have any examples. Try searching...

Comment #11

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