364:) system the first shutter curtain had the lens-facing side coated with a computer generated pattern of white blocks to emulate an average scene. As the mirror flipped-up the metering cell in the base of the mirror box measured the light reflected from the subject bouncing off this pattern of blocks. The timing of the release of the second curtain was adjusted in real time during the actual exposure. As the shutter speed increased, the actual light reflecting off the film surface was measured and the timing of the second curtain's release adjusted accordingly. This gave cameras equipped with this system the ability to adjust to changes in lighting during the actual exposure which was useful for specialist applications such as photomicrography and astronomical photography.
268:, where metering cells located at the bottom of the mirror box were used for ambient light metering, depending on model either instead or in addition to metering cells in the roof of the camera. Depending on model, the light was reflected down there either by a secondary mirror behind the half-transparent main mirror, a special reflective coating of the first shutter curtain, the surface of the film itself, or combinations thereof. One of the advantages of this approach is that the measuring result requires no adjustments when changing focusing screens or viewfinders. Also, some of the cameras using this configuration (e.g. the Minolta 9000) are virtually immune against measurement errors caused by light reaching the metering cells at larger angles, for example with
97:, the mechanism by which a SLR allows the viewfinder to see directly through the lens. As the mirror is flipped up, no light can reach there during exposure, the necessary amount of exposure needs to be determined before the actual exposure. Consequently, these light sensors could traditionally be used for ambient light TTL metering only. In newer SLRs as well as in almost all DSLRs, they can also be utilized for preflash TTL metering, where the metering is carried out before the mirror flips up using a small preflash of known intensity and the necessary amount of flash light is extrapolated from the reflected flash light measured by the metering cells in the roof of the camera and is then applied during the exposure without any possible real-time feedback.
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controlled to allow for proper exposure on the subject, thus leaving the background underexposed. Alternatively, if the lens is focused on the background, the background will be properly exposed, leaving the subject in the foreground typically overexposed. This technique requires both a camera capable of calculating the distance information, as well as the lens being capable of communicating the focal distance to the body. Nikon refers to this technique as "3D matrix metering", although different camera manufacturers use different terms for this technique. Canon incorporated this technique in E-TTL II.
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selected. The camera sets the exposure in order to get that particular spot properly exposed. On some modern SLR systems the spot metering area or zone can be coupled to the actual focusing area selected offering more flexibility and less need to use exposure lock systems. With multiple segment metering (also known as matrix or honeycomb metering), the values of the different segments are combined and weighted to set the correct exposure. Implementations of these metering modes vary between cameras and manufacturers, making it difficult to predict how a scene will be exposed when switching cameras.
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and types of film reflect the light to the same amount although the actual difference between brands was less than half a stop. The one exception was
Polaroid's instant slide film which had a black surface and could not be used in TTL flash mode. Nevertheless, for most applications analogue TTL flash exposure metering was more advanced and accurate than systems used previously and permitted far more flexibility - with bounced flash exposures in particular being more accurate than manually calculated equivalents.
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usually controls the remote flashes by using flashes of visible or infrared light, although TTL-capable radio triggering systems are available. The photographer can normally vary the light ratios between the different flashes. The technique of using preflashes to get a proper exposure is still used in automatic flash modes.
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Digital TTL works as follows: Before the actual exposure one or more small flashes, called "preflashes", are emitted. The light returning through the lens is measured and this value is used to calculate the amount of light necessary for the actual exposure. Multiple pre-flashes can be used to improve
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The analog version of TTL works as follows: when the incoming light hits the film, a part of it is reflected towards a sensor. This sensor controls the flash. If enough light is captured, the flash is stopped. During early testing of this system by
Minolta and Olympus it was found that not all brands
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digital cameras, which use the image sensor for exposure metering all the time. As of 2012, no digital SLR or SLT camera on the market supported any form of real-time TTL flash metering using the image sensor. However, it can be expected that such methods will be introduced as image sensor technology
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In many advanced modern cameras multiple 'segments' are used to acquire the amount of light in different places of the picture. Depending on the mode the photographer has selected, this information is then used to correctly set the exposure. With a simple spot meter, a single spot on the picture is
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When using front-curtain flash (when the flash fires immediately after the shutter opens), the preflashes and main flash appear as one to the human eye, since there is very little time between them. When using rear-curtain flash (when the flash fires at the end of the exposure) and a slow shutter
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More advanced TTL flash techniques include off-camera flash lighting, where one or more flash units are located at different locations around the subject. In this case a 'commander' unit (which can be integrated in the camera body) is used to control all of the remote units. The commander unit
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Some cameras and flash units take more information into account when calculating the necessary flash output, including the distance of the subject to the lens. This improves the lighting when a subject is placed in front of a background. If the lens is focused on the subject, the flash will be
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The process of calculating the correct amount of flash light can also be done 'through the lens'. This is being done in a significantly different way than non-flash 'through the lens' metering. The actual metering itself happens in two different ways, depending on the medium. Digital TTL works
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Some early Pentax DSLRs could use this same configuration for TTL flash metering as well, but since the reflectance properties of image sensors differ significantly from those of film, this method proved to be unreliable in practice. Therefore, digital SLR cameras typically don't support any
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With digital, this way of direct reflection metering is not possible any more since a CMOS or CCD chip, used to collect the light, is not reflective enough. There are a few older digital cameras which still use the analog technique, but these are getting rare. The
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camera. A variation of this "OTF" system was used on early
Olympus E-Series digital cameras to fine-tune the exposure just before the first curtain was released; for this to work, the first curtain was coated in a neutral grey colour.
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camera, which measured the exposure directly off the film (OTF). In OTF metering used by
Olympus, metering was performed in one of two ways — or a combination of both — depending upon the shutter speed in use.
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real-time TTL flash metering and must use preflash metering instead. The ambient and flash light metering is then carried out by a metering module located in the roof of the camera (see above).
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Metering cells located at the bottom of the mirror box using light reflected off the film are also used in all film SLRs supporting the classical form of real-time TTL flash metering.
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Digital SLRs supporting live view or video will use the read out of the image sensor itself for exposure metering in these modes. This also applies to
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In most film and digital SLRs, the light sensor(s) for exposure metering are incorporated into the
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TTL metering systems have been incorporated into other types of cameras as well. Most digital "
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The Nikon
Creative Lighting System: Wireless, Remote, Through-the-Lens Metered (iTTL) Flash!
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progresses, given the advantages of metering with real-time feedback and without preflash.
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was the first manufacturer to show an early prototype 35 mm behind-the-lens metering
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The first camera to feature through-the-lens light metering was by
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speed, the distinction between the main flash and the preflashes is more obvious.
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whereby the intensity of light reflected from the scene is measured through the
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S1 and S3 are the most well known digital cameras to use this technique.
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There were a few particularly sophisticated film SLRs including the
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70:), it can also be used to control the amount of light emitted by a
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610:, from "Flash Photography with Canon EOS Cameras" by N. K. Guy
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Below the mirror, reflecting off the film or shutter curtain
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Through-the-lens metering is most often associated with
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Crush, Darren (Spring 2012). "Budget TTL flashguns".
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Location of TTL light metering sensors in SLR cameras
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581:. Peterborough: Bauer. pp. 118–121, 123.
370:later used a variation of this system, as did
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416:(E-TTL) and later improved the system with
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501:"Olympus OM Flash Photography - Part 1"
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133:Above viewfinder in the pentaprism box
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396:differently than analog TTL.
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478:Stephen Gandy's CameraQuest
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537:Guide to Nikon TTL Flashes
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161:Side of the condenser lens
74:connected to the camera.
39:) refers to a feature of
33:through-the-lens metering
295:point-and-shoot cameras
608:How TTL metering works
324:, which was named the
640:Photography equipment
635:Photographic lighting
579:Practical Photography
358:Auto Dynamic Metering
344:Off the film metering
316:The Japanese company
614:The TTL Flash System
474:"Nikon Shibata Book"
332:show. The first TTL
630:Japanese inventions
616:, by Moose Petersen
84:single-lens reflex
336:SLR was the 1963
270:tilt–shift lenses
68:average luminance
16:(Redirected from
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374:with their
95:pentamirror
78:Description
49:light meter
29:photography
624:Categories
505:MIR.com.my
483:2008-06-08
459:References
448:Speedlight
322:SLR camera
264:, and the
91:pentaprism
72:flash unit
595:749128201
587:0032-6445
539:photo.net
382:) in the
258:Pentax LX
243:Zenit-TTL
208:Pentax LX
180:Leicaflex
164:Canon F-1
144:Canon EOS
559:23 April
510:23 April
436:See also
418:E-TTL II
406:Fujifilm
262:Nikon F3
184:Nikon F3
148:Zenit-12
140:Nikon FM
64:exposure
305:History
41:cameras
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446:Nikon
372:Pentax
318:Pentax
284:Sony's
260:, the
256:, the
368:Leica
311:Nikon
591:OCLC
583:ISSN
561:2018
512:2018
350:OM-2
57:film
45:lens
380:IDM
362:ADM
287:SLT
93:or
59:or
27:In
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