Difference between revisions of "TTL"

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The acronym '''TTL''' can refer to:
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{{glossary}}
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;Through The Lens: Usually referring to in-camera [[camera#TTL Metering|exposure metering]] or flash exposure control, but also used to differentiate [[viewfinder]] designs, [[autofocus]] mechanism designs, and other systems on lens-based cameras.  Measuring light or focusing through the taking lens can be more accurate than separate metering, viewfinder or focus systems, as this measures the light that will reach the film, from the exact point-of-view of the lens - and so eliminates [[parallax]] and stray light from outside the frame.
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;The acronym '''TTL''' most commonly refers to,
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{{Flickr_image
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|image_source= https://www.flickr.com/photos/vox/51230035316/in/pool-camerawiki/
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|image= https://live.staticflickr.com/65535/51230035316_ca1f0f4f9f_n.jpg
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|image_align= right
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|image_text= A diagram from [[Ricoh]] indicates two approaches<br>to TTL exposure metering
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|image_by=
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|image_rights= fair use
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}}
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'''Through The Lens''': referring to in-camera focusing (reflex cameras) or  [[camera#TTL Metering|exposure metering]] with photocells somewhere in the light path of the taking lens.  This was an improvement over older designs where a [[CdS]] or [[Selenium meter | selenium]] meter cell was attached somewhere atop the camera body, but could not take into account light loss from filters, lens extension, etc.  TTL exposure metering was possible in the 1960s after the introduction of [[CdS]] cells that were small enough to fit in a camera body.
  
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;Transistor-Transistor Logic: TTL is a type of digital electronic circuitry which uses transistors and resistor elements (usually made of transistors) to make logic gates. It is rarely, if ever used in camera circuitry as it has fairly high power consumption. Other logic families, with low power demands  are used, so as to prolong battery life - for example CMOS (Complementary Metal-Oxide Semiconductor) or even IIL (Integrated Injection Logic, used in the [[Canon A-1]]).
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TTL flash exposure control is another common meaning. But depending on context the term might also differentiate [[viewfinder]] designs, [[autofocus]] mechanism designs, or other camera systems.
  
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Electronic camera circuitry, digital electronics, the ability of a device or circuit to be connected directly to the input or output of digital equipment, eliminates the need for interfacing circuitry, TTL signals are usually limited to two states, low and high, and are thus much more limited than [[analog]] signals.
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;But,
  
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'''Transistor-Transistor Logic''': TTL is a type of digital electronic circuitry which uses transistors and resistor elements (usually made of transistors) to make logic gates. It is rarely, if ever used in camera circuitry as it has fairly high power consumption.
  
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{{glossary}}
 
 
[[Category:Abbreviations]]
 
[[Category:Abbreviations]]

Latest revision as of 12:33, 14 April 2024

Glossary Terms
The acronym TTL most commonly refers to,
51230035316_ca1f0f4f9f_n.jpg
A diagram from Ricoh indicates two approaches
to TTL exposure metering (Image rights)

Through The Lens: referring to in-camera focusing (reflex cameras) or exposure metering with photocells somewhere in the light path of the taking lens. This was an improvement over older designs where a CdS or selenium meter cell was attached somewhere atop the camera body, but could not take into account light loss from filters, lens extension, etc. TTL exposure metering was possible in the 1960s after the introduction of CdS cells that were small enough to fit in a camera body.

TTL flash exposure control is another common meaning. But depending on context the term might also differentiate viewfinder designs, autofocus mechanism designs, or other camera systems.

But,

Transistor-Transistor Logic: TTL is a type of digital electronic circuitry which uses transistors and resistor elements (usually made of transistors) to make logic gates. It is rarely, if ever used in camera circuitry as it has fairly high power consumption.

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