Not really clear on EV steps...

Discussion in 'Miscellaneous Equipment' started by AutumnJazz, Jun 10, 2008.

  1. AutumnJazz

    AutumnJazz Member

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    Ok, I have a question. Let's say I have a light meter, camera in manual mode, and a filter on my lens. That filter is +1.3 stops (or whatever). I use the light meter to find the correct exposure. Can I correct for the filter by setting my camera +1.3 EV steps?

    Thanks...
     
  2. matt miller

    matt miller Subscriber

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    You sure can.
     
  3. Kino

    Kino Member

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    Errr... wouldn't you subtract the EV? I mean, aren't you loosing the light rather than gaining it?

    Guess it's all how you phrase it...

    Open up 1.3 stops

    Reduce metered amount by 1.3 EV

    Lower your ASA by a factor 1.3 or about 80%

    All the same thing.
     
    Last edited by a moderator: Jun 11, 2008
  4. Leon

    Leon Member

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    I always find exposure compensation/ film speed adjustments etc terminology very confusing. The key thing to remember is the filter reduces the amount of light entering the camera, so you want to compensate for this by allowing more light in so, yes, setting auto exposure comp to + 1.3 would be perfect, or slowing down the film speed by 1.3 stops to force a slower speed would also work fine.

    whoops - I wrote this not realising I've echoed what Kino and Matt have said - I think matt puts it best.
     
  5. AutumnJazz

    AutumnJazz Member

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    How do you calculate it as a factor of film speed (ISO/ASA)?
     
  6. matt miller

    matt miller Subscriber

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    You can lower your film speed rating by the filter factor when metering. If you're using 400 speed film, and usually meter at 400, then you can set your meter to 160 (with your 1.3 stop example) to get the proper exposure.
     
  7. rwyoung

    rwyoung Member

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    Powers of 2 are your friend. " ^ " means "raise to the power of" in this example.

    Film Speed / (2 ^ factor) = new speed

    factor = 1.3
    Film Speed = 100
    new speed = 100 / (2 ^ 1.3) = 40.61

    But as you may have noticed, you don't have 40.61 as an option for film speed. Set to the closest value on your dial and be happy, probably 40.

    You can carry around a cheap (seen them for $5) calculator, or make up some cheat sheets (Excel / OpenOffice) or remember a few "tricks" and simply count 1/3 or 1/2 stops on the dials.
     
  8. Kino

    Kino Member

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    That's probably where we are differing; I am assuming a change of EV value on a hand held meter and I think (correct me if I am wrong) you are speaking of exposure compensation adjustments on a camera; right?

    And, you are right, it is always confusing...
     
  9. Leon

    Leon Member

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    Kino - I assumed the OP was referring to camera auto compensation, so that is what i was referring to, but probably just clouded matters more. this kind of thing can drive me nuts! recently, fellow apugger Stoo Batchelor came round for a cup-a-tea and we were trying to work out matching his spot meter readings with a 1.3 stop auto compensation on his camera - a simple thing on the face of it, but it took us ages to work out that what he was doing was right in the first place. Bloody Nightmare :smile:
     
  10. eddym

    eddym Member

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    It's not hard at all once you learn to "think in f-stops." The first thing to learn is the film speeds, which progress in 1/3 stop increments, as follows, and starting from 25:
    25 32 40 50 64 80 100 125 160 200 250 320 400 500 650 800 1000 1250 1600 etc.
    The numbers are easy to remember once you notice that each third number is doubled: 25 50 100 200; 32 64 125 250; 40 80 160 320

    And of course, each third film speed is a full stop faster or slower, depending on the direction you move.

    Full f-stops are also a numerical progression; every other one is doubled:
    f1.4 2.0 2.8 4 5.6 8 11 16 22 45 etc.

    To apply compensation, all you have to know is whether you are opening up or stopping down, and how many stops.
     
  11. AutumnJazz

    AutumnJazz Member

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    This post is exactly what I've been looking for since I started photography again. I pretty much forgot the basics. I'd been able to piece nearly everything back together except for the above.

    I love you!:tongue:
     
  12. HarryW

    HarryW Member

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    Hello,
    This is a very helpful thread and Eddy makes it very clear on the relationship of film speed and f-stops. I do however want to make sure that I am clear on this - is the original poster and the responses dealing only with a hand held meter and a non-metered camera? What I have never been clear on is if you use a filter on a TTL metered camera does the TTL metering system fully take care of the reduction in light getting to the film or are there circumstances where you would have to make additional compensation to the TTL meter reading.
    Regards
    Harry
     
  13. John Koehrer

    John Koehrer Subscriber

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    HarryW,
    Yes, The meter compensates, sort of.
    But. The meter doesn't have the same response to color that film does. So in theory it's not 100% accurate. The question is can the differences be seen.
    Try exposing the same scene with and without the filter & process the film.
    The exposures should be very close. If not you need to provide a bit of a fudge factor.
     
  14. HarryW

    HarryW Member

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    John,
    Thank you for this response. It's good to know and I guess that I will try this over the coming days. I should however have been more specific in my question and it relates to very dark filters in b+w photography for example a dark red (Nikon R60) to give really dark skies. I have never had much success with this filter and I don't have the filter factor for the R60 however I have seen 4-6 stated on the internet (which I assume equates to 2-3 stops). Is it best to use a handheld meter and adjust manually, or use a TTL meter and bracket when using dark filters?
    Regards
    Harry
     
  15. John Koehrer

    John Koehrer Subscriber

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    HarryW,
    I've never been one to do things the easy way.
    Personally I'd be inclined to the test exposure/process with each of the darker filters rather than ttl. You could use the in-camera meter and adjust for a tested compensation or use a dial in +X compensation.
    Or, bracket. I would think to the side of overexposure rather than under.