Glossary of terms

Discussion in 'Digital Photography' started by atwl77, Aug 18, 2003.

  1. atwl77

    atwl77 Just Started

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    Glossary of camera and photographic terms, in "English"
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    Aperture
    Refers to the size of the opening of the lens that allows light to enter. A large aperture is represented by a small F-number (e.g. F2.0) whereas a small aperture is represented by a large F-number (e.g. F8.0). Lenses with large apertures are considered fast because they allow more light to go through to the sensor.

    Depth of field
    Refers to the the distance where objects are in focus. Anything closer to, or further away from, this distance will be out of focus. Aperture size has a direct effect on DOF. A larger aperture will result in a shallow DOF while a smaller aperture will produce a deeper DOF.

    Exposure
    A term that determines how much light has hit a negative or sensor. A picture requires an exact amount of light (depending on lighting conditions) in order to get a good image. If too much light has hit the sensor, the image is over-exposed and is too bright. If too little light has hit the sensor, the image is under-exposed and is too dark. Exposure is controlled by 3 factors - aperture, shutter speed and ISO.

    ISO
    In film, this is the film's sensitivity to light. A lower ISO is less sensitive to a higher ISO film. The tradeoff for using a higher ISO is film grain. In digital cameras, increasing ISO amplifies the signal received on the camera's sensor. Boosting ISO will also amplify electrical noise which results in a random pattern of coloured dots in photos taken with high ISO.

    Metering
    The method that a camera uses to determine a correct exposure based on available light. Most digital cameras have three basic methods of metering:
    Wide area-based: Methods such as ESP, multi-spot and 3D Matrix metering are based on evaluating the whole frame (or multiple points on a frame) and deciding exposure based on a complex calculation.
    Centre-weighted: This is similar to an ESP or multi-spot but more emphasis is given on the area in the middle of the frame.
    Spot: Exposure is based on a single point which is usually at the middle of the frame.
    Partial: Metering is based on a small circle in the middle of the viewfinder which has a larger area than spot metering but doesn't take into account the rest of the scene as in centre-weighted metering.

    Mirror lockup
    In SLR cameras, a mirror reflects light into the viewfinder. When pressing the shutter button, the mirror moves up and out of the way so that the path of the light will reach the film/sensor and record the image. However, for extreme macros or slow shutter speed shots, this reflex action can sometimes induce camera shake. Mirror lockup is a feature that allows the mirror to flip up beforehand, and then the shot taken later to prevent this camera shake from occuring.

    Shutter speed
    In film, determines how fast the lens opens to allow light to hit the negative before closing. In digital, it basically refers to the same thing as film but may be implemented differently depending on whether the camera has a mechanical or digital shutter.
    Mechanical: The iris of the lens actually opens to let light in, then closes. A digital camera's sensor will only record the light that hits the sensor.
    Digital: The sensor will only record light that hits the sensor for a certain time period even though the lens continues to stay open and receive light.



    I will continue to update this list as time permits.
    :)atwl
     
  2. Jeremy

    Jeremy Black Sheep

    Hey, I've got a PDF document that lists the entire glossary of digital cameras from Olympus. Perhaps I could get either Chai or Peaz to upload it for you guys. Cheerz!
     
  3. ZuePhok

    ZuePhok Just Started

    black sheep black sheep..can u send it to me???????? need one sooooooooooo badly..

    thanks
     
    Last edited: Sep 30, 2010
  4. Jeremy

    Jeremy Black Sheep

    ZuePhok: Check your eMail and if possible pass it to Chai or Peaz so they can have it uploaded cause my online presence has been severely limited.
     
  5. ZuePhok

    ZuePhok Just Started

    alrite sure.

    THANKSSSSSSSSSS
     
  6. Got bored, though I would add to glossary. Did wanna (couldn’t be ass) re-phrasing RN def, so I did a reference

    RN-

    Random noise (RN) arises from

    -primarily thermal fluctuations in the electronic components that handle the analog CCD output signal

    -quantum (statistical) fluctuations in the numbers of photons reaching CCD sensels from the scene

    RN varies unpredictably, both in time and across the image frame. Since RN is uncorrelated, it can be reduced effectively by image averaging, a technique well known to CCD astronomers, professional and amateur alike. For every N identical exposures averaged together, the RN-related signal-to-noise ratio increases by a factor of sqrt(N).

    REF: http://dpfwiw.com/exposure.htm


    note: http://dpfwiw.com/exposure.htm is well worth a read (not my site)
     
  7. Ishtim

    Ishtim Super Moderator

    In response to atwl's post on the moon shot with his 1632mm focal length I was wondering about magnification and how it differs between 35mm film SLR & some of today's DSLRs. :think:

    Magnification...at least how I understand it...

    If you are using 35mm film, just divide lens focal length by 50. Use 50 because a 50mm lens is considered "normal" or closest to the human eye(1x magnification) for a 35mm camera. If additional lenses or multipliers are used to increase the focal length to "telephoto" sizes, say 1000mm, you would get 20 times the normal magnification or 20x (1000/50).

    My 300D and atwl's 10D cameras have a "Crop" factor of 1.6X that effectively increases the focal length. Now the 1000mm lens would behave as 1600mm or 32X magnification. The "crop" is created by the difference in "sensor" sizes between the 35mm (36x24mm) and CMOS (22.7x15mm) sensor.


    Feel free to correct me or add to this definition so that everyone (including myself) have a better understanding of what/how magnification is determined. :arp:
     
  8. doraemon

    doraemon Newbie

    Exposure times, aperture settings and film speed

    Found something useful to share:D
     

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