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Thread: Calculating number of stops

  1. #1

    Default Calculating number of stops


    I read somewhere in a magazine. The author set camera to AP mode and had an exposure of 1/2s. He moved 5 stops and achieved 1/30s. I was trying to figure out how to calculate number of stops. My calculations was obviously wrong as I thought 1/30s was 4 stops, not 5.

  2. #2

    Default Re: Calculating number of stops

    1/2, 1/4, 1/8, 1/15, 1/30

    its 4 stops.

    but i dun understand the whole concept.

    set to AP, then underexpose by 5 stops?

    but then, in AperturePriority mode, u cant underexpose. by adjusting the aperture, the shutter speed automatically changes to accomodate it (the aperture) to achieve the rite exposure.

    in Av, u can compensate exposure by the ExposureCompensation dial. but i doubt 5 stop over/under is possible. my 30D cant.

    which magazine are u reading?

  3. #3

    Default Re: Calculating number of stops

    He didn't say the author underexposed, merely moved 5 (it should be 4 by my count too) stops. Moving from f/11 and 1/2s to f/2.8 and 1/30s for example will give him the same exposure settings.

  4. #4
    Moderator catchlights's Avatar
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    Sep 2004
    Punggol, Singapore

    Default Re: Calculating number of stops

    4 stops difference
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  5. #5
    Member gymak90's Avatar
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    Jan 2008
    The Far North

    Default Re: Calculating number of stops

    What magazine is that? It's clearly 4 stops and not 5.

    To attap seed: No the magazine didn't say it was underexposed.
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  6. #6
    Senior Member
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    Apr 2008
    Singapore, east-ish

    Default Re: Calculating number of stops


    What magazine was that?

  7. #7

    Default Re: Calculating number of stops

    oic. i mis-understood.

    cus, i feel that its redundant to say, set to Av mode, had a exposure of 1/2 sec, then adjust to 1/30 sec.

    cus, if i set to Av, if i need f11, i jus set to f11. i wun say, from 2.8, i adjust 4 stops to f11.

  8. #8

    Default Re: Calculating number of stops

    I'm guessing it's probably an article to illustrate how to get a more handhold-able shutter speed while keeping the same exposure, in which case (error in stop calculation aside) it illustrates the point pretty well.

  9. #9

    Default Re: Calculating number of stops


    Thanks for clarifying.

    Let me clarify the situation it was used. Sorry for causing the confusion as my question was phrased to get the answer and not whats the situation.

    It was basically about setting to AP and do spot metering of multiple points before changing to manual mode and shoot.


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