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Thread: Correct Aperture value ???

  1. #1
    Senior Member melvin's Avatar
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    Default Correct Aperture value ???

    Hi!

    Came across this formula:

    Correct Aperture value = aperture on index times(x) focal length divded by sum focal length and extension.

    Is this useful?
    Does anyone still use this?
    Or is there a better alternative?
    Is it necessary nowadays?

    Pls enlighten thks!

  2. #2
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    Default Re: Correct Aperture value ???

    Quote Originally Posted by melvin
    Hi!

    Came across this formula:

    Correct Aperture value = aperture on index times(x) focal length divded by sum focal length and extension.

    Is this useful?
    Does anyone still use this?
    Or is there a better alternative?
    Is it necessary nowadays?

    Pls enlighten thks!
    what correct aperture?

  3. #3
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    Default Re: Correct Aperture value ???

    Quote Originally Posted by ExplorerZ
    what correct aperture?
    .

    in olden days of manual camera and flash, it is neccessary to get the correct aperture when using extension tube so that you can set the flash output.even auto flash like vivitar 283/285 needs user to dial in aperture

    today, almost all camera uses TTL flash metering. so the final aperture w ext is not that neccessary. plus w digital, you just see result then compensate your flash output accordingly
    Last edited by surge; 24th August 2006 at 11:21 AM.

  4. #4

    Default Re: Correct Aperture value ???

    I'm no expert, but that sounds like the formula for exposure correction for bellows extension when shooting large format.
    sk.images, ex - cyber_m0nkey

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    Default Re: Correct Aperture value ???

    Quote Originally Posted by surge
    .

    in olden days of manual camera and flash, it is neccessary to get the correct aperture when using extension tube so that you can set the flash output.even auto flash like vivitar 283/285 needs user to dial in aperture

    today, almost all camera uses TTL flash metering. so the final aperture w ext is not that neccessary. plus w digital, you just see result then compensate your flash output accordingly
    ic, haha i tot the extension he mention is the increase of lens length when you zoom in/out lol (non internal-zooming)

  6. #6

    Default Re: Correct Aperture value ???

    Quote Originally Posted by cyber_m0nkey
    I'm no expert, but that sounds like the formula for exposure correction for bellows extension when shooting large format.
    It is and 'surge' has already supplied an answer.

    You will need to use this formula if you use an external light meter and especially when doing Macro because the extension is much more that the reduction is significant.

  7. #7

    Default Re: Correct Aperture value ???

    Quote Originally Posted by lsisaxon
    It is and 'surge' has already supplied an answer.

    You will need to use this formula if you use an external light meter and especially when doing Macro because the extension is much more that the reduction is significant.
    I was typing while surge was posting. Surges response also related to flash, whereas my response relates to non-flash exposures for LF photoraphy.
    sk.images, ex - cyber_m0nkey

  8. #8

    Default Re: Correct Aperture value ???

    Quote Originally Posted by cyber_m0nkey
    I was typing while surge was posting. Surges response also related to flash, whereas my response relates to non-flash exposures for LF photoraphy.
    Yes. 'It is' refers to your comment and the rest is just general comments for the TS. If I hadn't read on, I might have repeated what 'surge' and you have written.

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    Default Re: Correct Aperture value ???

    Quote Originally Posted by ExplorerZ
    ic, haha i tot the extension he mention is the increase of lens length when you zoom in/out lol (non internal-zooming)
    zoom lens move the elements when you zoom in or out. this changes the distance between elements to film plane thus changing the aperture ( variable aperture). even macro lens like the 60/2.8 nikkor does the same, be increase the len to film distance, its like a built in ectension tube in the lens.

  10. #10
    Senior Member melvin's Avatar
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    Default Re: Correct Aperture value ???

    Quote Originally Posted by surge
    .

    in olden days of manual camera and flash, it is neccessary to get the correct aperture when using extension tube so that you can set the flash output.even auto flash like vivitar 283/285 needs user to dial in aperture

    today, almost all camera uses TTL flash metering. so the final aperture w ext is not that neccessary. plus w digital, you just see result then compensate your flash output accordingly
    Thanks! For the info!
    So if thats the case meaning i can safely ignore the formula if we are using digital?

  11. #11

    Default Re: Correct Aperture value ???

    Quote Originally Posted by melvin
    Thanks! For the info!
    So if thats the case meaning i can safely ignore the formula if we are using digital?
    You can ignore the formula whenever using TTL metering, film or digital.
    sk.images, ex - cyber_m0nkey

  12. #12
    Senior Member melvin's Avatar
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    Default Re: Correct Aperture value ???

    Quote Originally Posted by cyber_m0nkey
    You can ignore the formula whenever using TTL metering, film or digital.
    Thanks! I am bad wif formula

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