Difference between revisions of "Exposure meter"

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(intro rephrasing; noted DR limit as reason meters are needed)
(Early exposure meters: /photos/29504544@N08/48651949687 added from pool)
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{{glossary}}
 
{{glossary}}
At best, photographic film or digital sensors are only able to record a range of brightness of roughly 1000:1 (10 stops)—significantly poorer than human vision. Thus a camera's exposure settings must be adjusted so that no significant highlight or shadow detail falls outside the range that can be recorded.
+
{{Flickr_image
 +
|image_source= http://www.flickr.com/photos/phollectormo/5539013627
 +
|image= http://farm6.staticflickr.com/5058/5539013627_7e09766ab4.jpg
 +
|image_align= right
 +
|image_text= Meters
 +
|image_by= phollectormo
 +
|image_rights= wp
 +
}}
 +
 
 +
At best, photographic film or digital sensors are only able to record a range of scene brightness of roughly 1000:1 (10 stops)—significantly poorer than human vision. Thus, a camera's exposure settings must be adjusted so that no significant highlight or shadow detail falls outside the range that can be recorded.
 +
 
 +
An '''exposure meter''' (short form ''meter'', commonly '''light meter''') is an instrument that measures light and can calculate exposure settings, taking account of film or sensor sensitivity (ASA/DIN).
 +
 
 +
Whilst the two terms "light meter" and "exposure meter" are often used interchangeably, there is a difference:
 +
*Light meters display lux or footcandles and are used to measure absolute light intensity, such as assessing proper lighting levels in a work environment (photometry or photometric reading). Measurement is always incident using a flat diffuser to measure only the source light.
 +
*Exposure meters have, in addition, a calculator to display computed exposure settings for a camera, taking film / sensor sensitivity into account. Measurement can be reflected, or incident using a domed diffuser which also takes account of reflected light.
 +
 
 +
Some professional meters can make both types of measurement.
 +
 
 +
==Incident & reflected measurement==
 +
Built in camera meters always measure reflected light, with variations due to reflectivity of the subject, which is why exposure compensation is provided. Hand held meters may also measure incident light (i.e. source light) using a translucent dome, which eliminates variations due to the subject. Taking a reflected reading from an 18% grey card is equivalent to an incident reading.
 +
 
 +
For reversal (slide) film or electronic cameras incident light measurement is usually preferred since final image intensity depends only on the captured intensity.
 +
 
 +
For negative film, reflected measurement is often preferred since final image intensity can be adjusted in the enlargement process. By using reflected measurement, especially the zone system<REF>[http://en.wikipedia.org/wiki/Zone_System "Zone System"] article at [http://en.wikipedia.org/wiki/Main_Page Wikipedia].</REF>, a greater range of shadow to highlight detail may be recorded.
  
A '''light meter''' (or '''exposure meter''', short form ''meter'') is a device that measures light to determine the proper exposure settings for a scene. Analog measuring instruments with a [[selenium]] photoelectric cell as voltage source were the most common early models for the average photographer. Later, more light-sensitive meters were made, with Cadmium Sulfide ([[CdS]]) photo resistors or silicon photodiodes as sensors. The latter even respond quickly enough to evaluate the [[exposure value]] of flash exposure, and store it as a digital readout. But [[selenium meter]]s have not disappeared entirely, as they are the only type requiring no battery.
+
In a photographic studio incident readings will usually be used since the contrast range is carefully controlled.
  
== Early light meters ==
+
==Photoelectric cells==
 +
Analog measuring instruments with a [[selenium]] cell as voltage source were the most common early type of photoelectric light meter. Multiple "insect eye" lenses covering the photocell are very characteristic of a [[selenium meter]]. Like a small solar panel, the selenium cell generates its own electric current, which (typically) deflects an indicator needle by varying amounts.
 +
 
 +
Later, more sensitive meters were made, with Cadmium Sulfide ([[CdS]]) photo resistors or silicon photodiodes (PD, or SBC; 'silicon blue cell') as sensors . SBC sensors respond quickly enough to evaluate flash intensity. [[Selenium meter]]s have not disappeared entirely as they are the only type not requiring a battery.
 +
 
 +
==Meter types==
 +
===Mechanical scale===
 +
Mechanical scale (analog) meters usually have a large and distinctive circular scale, however some have a linear scale. This scale must first be aligned to the measured illuminance, but then the entire range of exposure settings can be read off.
 +
 
 +
The meter display can be the classic moving pointer, which may have a follow pointer to align the exposure scale. Null or zero pointer meters are aligned to a central "null" position (e.g. [[Gossen Profisix]]). A few electronic meters use an LED array for scale alignment.
 +
 
 +
===Digital===
 +
Digital meters do not have any mechanical component and display exposure settings digitally. A computed exposure setting is displayed immediately, however only one setting can be shown at a time and up&nbsp;/ down buttons are provided to scroll through the range of settings.
 +
 
 +
Many digital meters also display an analog like scale of the aperture setting to the nearest half stop.
 +
 
 +
== Early exposure meters ==
 
===Actinometers===
 
===Actinometers===
''[[Actinometry|Actinometers]]'' were the first light meters. They typically had the shape of a pocket watch and used light sensitive photo print paper as means of measuring. The time to darken a piece of such paper until it matches a standard tint is the input value for the scales on which an appropriate shutter-speed/aperture combination for the light situation can be found.
 
===Extinction Meters===
 
 
{{Flickr_image
 
{{Flickr_image
|image_source= http://www.flickr.com/photos/89864432@N00/4178486955/in/pool-camerapedia/
+
|image_source= http://www.flickr.com/photos/29504544@N08/48651949687/in/pool-camerawiki/
 +
|image= https://live.staticflickr.com/65535/48651949687_d64c23af4c_m.jpg
 +
|image_align= right
 +
|image_text= Haka Expometer c.1910
 +
|image_by= Hans Kerensky
 +
|image_rights=  with permission
 +
}}
 +
''[[Actinometry|Actinometers]]'' were the first exposure meters. They typically had the shape of a pocket watch and used light sensitive photo print paper as means of measuring. The time to darken a piece of such paper until it matches a standard tint is the input value for the scales on which an appropriate shutter-speed/aperture combination for the light situation can be found.
 +
{{br}}
 +
===Extinction meters===
 +
{{Flickr_image
 +
|image_source= http://www.flickr.com/photos/89864432@N00/4178486955/in/pool-camerawiki
 
|image= http://farm3.static.flickr.com/2785/4178486955_febab71d8a_m.jpg
 
|image= http://farm3.static.flickr.com/2785/4178486955_febab71d8a_m.jpg
 
|image_align= left
 
|image_align= left
 
|image_text= Logaphot extinction meter of 1955<br/>with slide-rule back to determine<br/>exposure settings for 100 [[film speed|ASA]]
 
|image_text= Logaphot extinction meter of 1955<br/>with slide-rule back to determine<br/>exposure settings for 100 [[film speed|ASA]]
 +
|image_by= Uwe Kulick
 +
|image_rights=  with permission
 
}}
 
}}
Another type of early meter, the ''extinction meter'', depended on eyesight: the user looks through the meter at a row of numbers, each behind a celluloid window of different opacity, the highest or lowest visible number determining which light situation is given. Other extinction meters have a pattern visible through the eyepiece, and a control varies the amount of light allowed into the device until the pattern can only just be seen; the position on the control then indicates the exposure.
+
Another early meter, the ''extinction meter'', depends on eyesight: the user looks through the meter at a row of numbers, each behind a celluloid window of different opacity, the highest or lowest visible number determining which light situation is given. Other extinction meters have a pattern visible through the eyepiece, and a control varies the amount of light allowed into the device until the pattern can only just be seen; the position on the control then indicates the exposure.
 
{{Flickr_image
 
{{Flickr_image
|image_source= http://www.flickr.com/photos/captkodak/271891485/in/pool-camerapedia
+
|image_source= http://www.flickr.com/photos/captkodak/271891485/in/pool-camerawiki
 
|image= http://farm1.static.flickr.com/106/271891485_cf66c25f63_m.jpg
 
|image= http://farm1.static.flickr.com/106/271891485_cf66c25f63_m.jpg
 
|image_align= right
 
|image_align= right
 
|image_text= Mimosa extinction meter of 1947
 
|image_text= Mimosa extinction meter of 1947
 +
|image_by= Steve Harwood
 +
|image_rights=  non-commercial
 
}}{{br}}
 
}}{{br}}
  
== Light meter makers ==
+
== Exposure meter makers ==
 
{{Flickr_image
 
{{Flickr_image
|image_source= http://www.flickr.com/photos/captkodak/271837535/in/pool-camerapedia/
+
|image_source= http://www.flickr.com/photos/captkodak/271837535/in/pool-camerawiki
 
|image= http://farm1.static.flickr.com/107/271837535_9989e5f4f2_m.jpg
 
|image= http://farm1.static.flickr.com/107/271837535_9989e5f4f2_m.jpg
 
|image_align= right
 
|image_align= right
 
|image_text= Bertram Chrostar Exposure Meter
 
|image_text= Bertram Chrostar Exposure Meter
 +
|image_by=Steve Harwood
 +
|image_rights=nc
 
}}
 
}}
 
* [[AVO]]
 
* [[AVO]]
Line 40: Line 95:
 
* [[Sekonic]]
 
* [[Sekonic]]
 
* [[Soligor]]
 
* [[Soligor]]
 +
* [[Vibrator]]
 +
* [[Vivitar#Light_Meters|Vivitar]]
 +
*[[Weigand|Weigand Messtechnik]]
 
* [[Weston]]
 
* [[Weston]]
 
* [[Zeiss Ikon]]
 
* [[Zeiss Ikon]]
Line 45: Line 103:
 
and many others; see [[:Category: Meter makers]].
 
and many others; see [[:Category: Meter makers]].
  
== Light meters in cameras ==
+
== Exposure meters in cameras ==
Automation of exposure control in cameras began with built-in [[selenium meter]]s. Shutter speed and aperture had to be selected manually according to the meter's absolute or relative measured values. With the advent of electrically controlled diaphragms and shutters other light sensors like photo resistors, photo diodes etc. became common parts in cameras. Both sorts of devices needed batteries for operation. Some additional electronic circuits combining meter with [[shutter]] and [[diaphragm]] units were just needed to get exposure control automated. This sort of camera emerged in the 1960ies.
+
The first camera to include a built-in meter was the 1935 Zeiss Ikon [[Contaflex (TLR)]], using a [[selenium]] cell. To give sufficient sensitivity, a selenium cell requires a certain surface area (roughly postage-stamp sized). When covered with "insect eye" lenses to give directivity, they dominated the appearance of many mid-century cameras. In the early 1960s, makers of cameras and light meters adopted the battery-powered [[CdS]] photoresistor as a sensor element, which could be much more compact. Finally, gallium arsenide and silicon photodiodes were adopted, for their faster response rate.
  
A camera's built-in light meter can easily be tricked into giving an incorrect exposure. The most common problem is a bright background behind the subject such as a bright sky, or bright light reflecting off snow, sand or water. Built-in meters often darken the photo excessively.
+
The earliest built-in meters had no coupling to the camera's shutter or aperture settings. The photographer was expected to set both manually, based on the reading given. Later meters were "semi-coupled": meter readings were adjusted according to one of the camera's settings, and the readout indicated how the user should set the other. Finally, both aperture and shutter speed settings were coupled
  
A hand-held meter is more accurate since it measures the light falling on the subject.  It is not fooled by a bright background.  Nor is it fooled by objects which reflect a great deal or very little light.
+
====Meter limitations and workarounds====
 +
A hand-held meter may be brought very close to a subject, or used to measure the light falling onto it, for a very accurate reading. A meter viewing light from the entire scene may give incorrect exposure, the most common problems being bright background behind the subject, such as a bright sky, or bright light reflecting off snow, sand, or water, leading to underexposure of the desired subject. Less commonly, dark backgrounds can also give incorrect readings.
  
Keep in mind that the camera's light meter is measuring the light reflected back off the subject. In simple terms, a green shirt appears green because it absorbs all the colors except green -- which it reflects back.  A white shirt reflects all the light, while a flat black surface would reflect none.
+
Built-in meters may use a metering pattern strongly weighted towards the center of the frame (or even just a small spot). Camera makers have added increasingly complicated multi-zone metering, designed to identify typical "tricky light" situations and compensate accordingly.
  
A dark-skinned black woman in a bright white wedding gown is a difficult/impossible subject that's sure to fool a camera's meter. (The classic wedding photographer's nightmare, either the gown or the face
+
For manual exposures, a solution is to walk closer to the main subject or zoom in with the lens, take a meter reading, and then recompose. The correct exposure value can also be read off a mid-toned 18-percent gray card held in front of the subject (or even the palm of the hand, then adjusting upwards by 1 stop). Like using an incident meter, this ensures that the light falling on the subject is measured, rather than the variable amounts reflected back towards the camera by a white wedding dress or a black cat.
can be exposed properly unless the photo is touched up after the fact using burning or dodging techniques.)
 
  
These problems can be corrected in a few ways. One solution is to zoom in on the desired subject so that less of the bright background/foreground is seen.
+
Many advanced cameras with autoexposure offer of Auto Exposure Lock (AE Lock, Exposure Memory Lock, or EV Lock). Using AEL, it's possible to selectively take a meter reading of the desired area of the subject (for instance the bride's face). With that value now locked in, the complete scene can be photographed at the locked exposure.
  
Advanced cameras offer some kind of Auto Exposure Lock (aka AE Lock, Exposure Memory Lock or EV Lock).  Using AEL, it's possible to zoom in or approach the subject so that an exposure value can be read from just the desired area of the subject (for instance the bride's face).  With that value now locked in, the complete subject area can now be
+
As well, the technique of exposure bracketing can be used. Bracketing ([[Exposure|Exposure & Exposure Bracketing]]) is the technique of taking multiple photos at different exposures to ensure at least one of them will be correctly exposed.
photographed at that exposure.
 
 
 
The correct exposure value can also be read off a neutral test card or 18 percent gray card (or even the palm of the human hand) held in front of the subject.  Like using a hand-held meter, this ensures that the light falling on the subject is measured, rather than what is reflected back by different surfaces like a bright white bridal gown.
 
 
 
As well, the technique of exposure bracketing can be used. Bracketing ([[Exposure|Exposure & Exposure Bracketing]]) is the technique of taking multiple photos at different f-stops to ensure at least one of them will be correctly exposed.
 
  
 
== Professional Meters ==
 
== Professional Meters ==
Line 70: Line 123:
 
* [[Spot meter]]s
 
* [[Spot meter]]s
 
* [[Flash meter]]s
 
* [[Flash meter]]s
 +
 +
==Notes==
 +
<references/>
  
 
== Links ==
 
== Links ==
 
+
* [http://www.jollinger.com/photo/meters/other/invention.html "Who Invented the Modern Exposure Meter?"] by [http://www.jollinger.com/photo/meters/index.html James Ollinger]
 
* [http://www.butkus.org/chinon/flashes_meters.htm  Light meter instruction manuals] www.orphancameras.com
 
* [http://www.butkus.org/chinon/flashes_meters.htm  Light meter instruction manuals] www.orphancameras.com
* [http://www.photo-manuals.com/tracking/33 Light Meter Manuals : Photo-Manuals.com] by Ben Squire.
+
* [http://www.photo-manuals.com/manual/sekonic/light-meter Sekonic Light Meter Manuals : Photo-Manuals.com]
 
* [http://www.jollinger.com/photo/meters/index.html James's Light Meter collection] contains images, reviews and instructions for a large number of vintage meters.
 
* [http://www.jollinger.com/photo/meters/index.html James's Light Meter collection] contains images, reviews and instructions for a large number of vintage meters.
 +
* [http://lightmetermuseum.com/Light%20meters/index.html Anssi's collection]
  
 
[[Category: meters|*]]
 
[[Category: meters|*]]
 
[[Category: Camera parts]]
 
[[Category: Camera parts]]
 
[[Category: Accessories]]
 
[[Category: Accessories]]

Revision as of 07:50, 31 August 2019

Glossary Terms

At best, photographic film or digital sensors are only able to record a range of scene brightness of roughly 1000:1 (10 stops)—significantly poorer than human vision. Thus, a camera's exposure settings must be adjusted so that no significant highlight or shadow detail falls outside the range that can be recorded.

An exposure meter (short form meter, commonly light meter) is an instrument that measures light and can calculate exposure settings, taking account of film or sensor sensitivity (ASA/DIN).

Whilst the two terms "light meter" and "exposure meter" are often used interchangeably, there is a difference:

  • Light meters display lux or footcandles and are used to measure absolute light intensity, such as assessing proper lighting levels in a work environment (photometry or photometric reading). Measurement is always incident using a flat diffuser to measure only the source light.
  • Exposure meters have, in addition, a calculator to display computed exposure settings for a camera, taking film / sensor sensitivity into account. Measurement can be reflected, or incident using a domed diffuser which also takes account of reflected light.

Some professional meters can make both types of measurement.

Incident & reflected measurement

Built in camera meters always measure reflected light, with variations due to reflectivity of the subject, which is why exposure compensation is provided. Hand held meters may also measure incident light (i.e. source light) using a translucent dome, which eliminates variations due to the subject. Taking a reflected reading from an 18% grey card is equivalent to an incident reading.

For reversal (slide) film or electronic cameras incident light measurement is usually preferred since final image intensity depends only on the captured intensity.

For negative film, reflected measurement is often preferred since final image intensity can be adjusted in the enlargement process. By using reflected measurement, especially the zone system[1], a greater range of shadow to highlight detail may be recorded.

In a photographic studio incident readings will usually be used since the contrast range is carefully controlled.

Photoelectric cells

Analog measuring instruments with a selenium cell as voltage source were the most common early type of photoelectric light meter. Multiple "insect eye" lenses covering the photocell are very characteristic of a selenium meter. Like a small solar panel, the selenium cell generates its own electric current, which (typically) deflects an indicator needle by varying amounts.

Later, more sensitive meters were made, with Cadmium Sulfide (CdS) photo resistors or silicon photodiodes (PD, or SBC; 'silicon blue cell') as sensors . SBC sensors respond quickly enough to evaluate flash intensity. Selenium meters have not disappeared entirely as they are the only type not requiring a battery.

Meter types

Mechanical scale

Mechanical scale (analog) meters usually have a large and distinctive circular scale, however some have a linear scale. This scale must first be aligned to the measured illuminance, but then the entire range of exposure settings can be read off.

The meter display can be the classic moving pointer, which may have a follow pointer to align the exposure scale. Null or zero pointer meters are aligned to a central "null" position (e.g. Gossen Profisix). A few electronic meters use an LED array for scale alignment.

Digital

Digital meters do not have any mechanical component and display exposure settings digitally. A computed exposure setting is displayed immediately, however only one setting can be shown at a time and up / down buttons are provided to scroll through the range of settings.

Many digital meters also display an analog like scale of the aperture setting to the nearest half stop.

Early exposure meters

Actinometers

Actinometers were the first exposure meters. They typically had the shape of a pocket watch and used light sensitive photo print paper as means of measuring. The time to darken a piece of such paper until it matches a standard tint is the input value for the scales on which an appropriate shutter-speed/aperture combination for the light situation can be found.

Extinction meters

Another early meter, the extinction meter, depends on eyesight: the user looks through the meter at a row of numbers, each behind a celluloid window of different opacity, the highest or lowest visible number determining which light situation is given. Other extinction meters have a pattern visible through the eyepiece, and a control varies the amount of light allowed into the device until the pattern can only just be seen; the position on the control then indicates the exposure.


Exposure meter makers

and many others; see Category: Meter makers.

Exposure meters in cameras

The first camera to include a built-in meter was the 1935 Zeiss Ikon Contaflex (TLR), using a selenium cell. To give sufficient sensitivity, a selenium cell requires a certain surface area (roughly postage-stamp sized). When covered with "insect eye" lenses to give directivity, they dominated the appearance of many mid-century cameras. In the early 1960s, makers of cameras and light meters adopted the battery-powered CdS photoresistor as a sensor element, which could be much more compact. Finally, gallium arsenide and silicon photodiodes were adopted, for their faster response rate.

The earliest built-in meters had no coupling to the camera's shutter or aperture settings. The photographer was expected to set both manually, based on the reading given. Later meters were "semi-coupled": meter readings were adjusted according to one of the camera's settings, and the readout indicated how the user should set the other. Finally, both aperture and shutter speed settings were coupled

Meter limitations and workarounds

A hand-held meter may be brought very close to a subject, or used to measure the light falling onto it, for a very accurate reading. A meter viewing light from the entire scene may give incorrect exposure, the most common problems being bright background behind the subject, such as a bright sky, or bright light reflecting off snow, sand, or water, leading to underexposure of the desired subject. Less commonly, dark backgrounds can also give incorrect readings.

Built-in meters may use a metering pattern strongly weighted towards the center of the frame (or even just a small spot). Camera makers have added increasingly complicated multi-zone metering, designed to identify typical "tricky light" situations and compensate accordingly.

For manual exposures, a solution is to walk closer to the main subject or zoom in with the lens, take a meter reading, and then recompose. The correct exposure value can also be read off a mid-toned 18-percent gray card held in front of the subject (or even the palm of the hand, then adjusting upwards by 1 stop). Like using an incident meter, this ensures that the light falling on the subject is measured, rather than the variable amounts reflected back towards the camera by a white wedding dress or a black cat.

Many advanced cameras with autoexposure offer of Auto Exposure Lock (AE Lock, Exposure Memory Lock, or EV Lock). Using AEL, it's possible to selectively take a meter reading of the desired area of the subject (for instance the bride's face). With that value now locked in, the complete scene can be photographed at the locked exposure.

As well, the technique of exposure bracketing can be used. Bracketing (Exposure & Exposure Bracketing) is the technique of taking multiple photos at different exposures to ensure at least one of them will be correctly exposed.

Professional Meters

Certain types of light meters are typical professional photographic tools:

Notes

Links