New to EV's

Discussion in 'Exposure Discussion' started by zackesch, Nov 6, 2012.

  1. zackesch

    zackesch Member

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    I received my grandfathers Kodak Pony II this weekend. Before I shoot my first roll, I have a few questions about EV’s. First, I’d like to note that the Pony II has a fixed shutter speed which is not specified by Kodak in the manual. I’ve read that it’s 1/60 or 1/125 shutter speeds, again not from Kodak.

    I understand that film speed was much lower then what it is today, and the slowest roll I had on hand was my Kodak MAX 200. I can adjust the EV ranging from 9.5 to 15. If my EV app is correct, set at 200 iso and 1/60 and 1/125 shutter speed, the equivalent f stop range is,
    1/60: f/4.0 to f/32, EV13 is f/16
    1/125: f/2.8 to f/22, EV 14 is f/16

    The EV card is showing EV 11.5 for sunny shots so I can only assume that would be f/16 for the sunny 16 rule.

    Do I have the right line of thought?
     
  2. zackesch

    zackesch Member

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  3. Hatchetman

    Hatchetman Subscriber

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    Hmmm. The camera was produced in 1957. Kodachrome was ASA 16 I think. So that would be four stops slower than 200 speed. So EV 7.5?

    I think your best bet is going to be to shoot a scene at various EV settings and develop the film to see what EV settings are correct.
     
  4. zackesch

    zackesch Member

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    If the film used was ASA 16, then the f stop range would be from 1.0 to 9.0.
     
  5. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    Plus-X's published speed when the camera was made was probably 80. Kodak removed a 'safety factor' in their published film speeds and so Plus-X became ASA 125, though the film didn't change.

    The Plus-X 80 card specifies EV 15 for bright sun. So, maybe the card reflected the true film speed without a safety factor. EV15 is 1/125 @ f/16 = 'sunny 16' for ASA 125.

    The shutter speed is 1/50th of a second, given EV9.5 for for its maximum f3.9 aperture lens and the formula EV = log2 (f^2/t), where t is in seconds.
     
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  6. Hatchetman

    Hatchetman Subscriber

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  7. andrew.roos

    andrew.roos Member

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    EV as used on old cameras and lenses does not depend on ISO, only on shutter speed and aperture. You can calculate EV as follows:

    For shutter speed (at aperture f/1):

    1 second = EV 0
    1/2 = EV 1
    1/4 = EV 2
    1/8 = EV 3
    1/15 = EV 4
    1/30 = EV 5
    1/60 = EV 6
    1/120 = EV 7

    For aperture, (at 1 second exposure)

    f/1.0 = EV 0
    f/1.4 = EV 1
    f/2.0 = EV 2
    f/2.8 = EV 3
    f/4.0 = EV 4
    f/5.6 = EV 5
    f/8.0 = EV 6
    f/11 = EV 7
    f/16 = EV 8
    f/22 = EV 9

    To get the EV corresponding to a particular shutter speed and aperture, simply add the EV I've listed for the shutter speed (at f/0) to the EV listed for the aperture (at 1 second). So EV for 1/120" and f/16 would be 7 + 8 = 15. This corresponds to the "Sunny 16" rule for ISO 120 film (since the shutter speed is 1/120"). So when you set EV 16 on the camera, if the built in shutter speed is fixed at 1/120" then you are simply setting the aperture to f/16.

    Originally EV ("Exposure Value") only referred to the factors affecting exposure (shutter speed and aperture) and not to the film sensitivity. Later on, EV was used as a measure of light intensity. In this case, ISO 100 is usually assumed. You have to figure out from context whether a use of EV refers to an exposure setting (as it does with the camera) or a light intensity (as is the case with light meters calibrated in EVs).

    So if you have a light meter calibrated in EVs (referenced to ISO 100) and you put ISO 100 film in the camera, then you can simply take the EV reading from the light meter and put it into the camera for a "correct" exposure. However, if you use a different ISO film then you need to adjust the EV reading from the light meter to account for the difference between the light meter calibration (usually ISO 100) and the actual film speed.

    For example, with ISO 400 film, you need to decrease the exposure by 2 stops compared to ISO 100. To do this you have to ADD 2 to the EV since increasing the EV by one reduces (makes darker) the exposure by one stop. If the light meter reads EV 10, then for 400 film you would set the camera to EV 12.

    Of course if the light meter includes an ASA setting (typically found on the calculator dial) then you may simply be able to set this to the ISO of the film you are using and then read the correct EV for that ISO from the meter, and then use it without any adjustment.

    The fact that your exposure cards specifies EV 11.5 for a sunny day suggests it was designed for film that is about 3.5 stops slower than ISO 120, hence somewhere around ISO 10.6 (calculated as 120 / 2^3.5). According to Wikipedia, Kodachrome daylight film in that era was ISO 10. The Type A film was ISO 16, for use indoors under floodlights (presumably for movies).
     
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  8. Ian C

    Ian C Member

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    I believe the Kodak Pony II has a 44mm f/3.5 lens with a fixed shutter speed of approximately 1/60 second.

    The aperture ring is marked EV 9.5 (approximately) to EV 15, so the aperture positions are likely:

    First lens marking (roughly EV 9.5) corresponding approximately to f/3.5

    EV 10 = f/4

    EV 11 = f/5.6

    EV 12 = f/8

    EV 13 = f/11

    EV 14 = f/16

    EV 15 = f/22

    This table should give you the approximate lens openings assuming a fixed 1/60-second shutter speed on the Kodak Pony II. This should allow using a standard light meter to accurately determine exposure by changing the aperture using the corresponding EV numbers on the lens scale.

    You’d prioritize the shutter speed on the meter at 1/60 second and take the reading. For example, if you got a meter reading of, say, f/8, you’d set the aperture ring to EV 12 = f/8.
     
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  9. zackesch

    zackesch Member

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    If EV is not effected by ASA, then how does ASA fit into the mix?
     
  10. FotoGys

    FotoGys Member

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  11. Ian C

    Ian C Member

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    ASA film speed is a numerical value describing the light sensitivity of the film.

    Exposure value is INDEPENDENT of film speed and expresses various combinations of shutter speed and aperture as a single numerical value.

    The Kodak Pony has its aperture marked in EV as a “simplification” for easier amateur use. At least that was the idea. It works on the Pony because it only has a single fixed shutter speed. With a camera with a variety of different shutter speeds, the idea of marking the aperture with EV numbers is impractical.

    Once you select a particular film, you have set the film speed. Now both the film speed (its sensitivity to light) and the shutter speed (1/60 second) are fixed. Each data card for the Pony was made to correspond to the film speed of a common Kodak film in use at the time the camera was made.

    All the user had to do was read the sky lighting conditions on the card to find the corresponding EV and set that value on the aperture ring.
     
  12. zackesch

    zackesch Member

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    So, if I understand this correctly, EV tabels are set at ASA 100. If I want to shoot at ASA 200 I add 1 to that EV. So, if I want to shoot EV 14 at 100 ASA, then EV is 14, then if i want to shoot ASA 200 at EV 14, I need to bump it up to EV 15. When the EV value is changed, the f stop will no longer be f/16 but f/22.
     
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  13. Steve Smith

    Steve Smith Member

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    EV - Exposure Value is a function of shutter speed and aperture only.

    LV - Light Value is a measure of the light only.

    At ISO 100 these numbers coincide. e.g. for ISO 100, an LV reading of 15 means you should use an EV setting of 15.

    At ISO 200, half as much light is needed so an LV reading of 15 will require an EV setting of 16.


    Steve.
     
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  15. BrianShaw

    BrianShaw Member

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    Clearly stated, Steve!
     
  16. Hatchetman

    Hatchetman Subscriber

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    And since the camera doesn't have an EV setting of 16, there is a problem! Stay in the shade!
     
  17. zackesch

    zackesch Member

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    Ok, I have a good understanding of it now. Thanks for your time.

    I noticed that hatchetman, no indoor shots with 200 ISO, and with overcast starting to be normal, Im not too worried about anything over EV 15.
     
  18. Steve Smith

    Steve Smith Member

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    I wouldn't worry about over exposing one or two stops!


    Steve.
     
  19. Hatchetman

    Hatchetman Subscriber

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    Good point. Digital habits are hard to break. :whistling:
     
  20. zackesch

    zackesch Member

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    Now I have some more photo info that I can entertain my wife with. After all, shes showing interest in B&W film. :D
    Ill start compairing the weather to an EV value, like looking out my window its now about EV 12. I'm sure she will love that.
     
  21. Steve Smith

    Steve Smith Member

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    No!!!


    You compare it with an LV level!!


    Steve.
     
  22. zackesch

    zackesch Member

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    Pardon the typo.
     
  23. BrianShaw

    BrianShaw Member

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    Your wife may never notice the typo. She'll likely smile and say, "yes, dear" no matter what you tell her. :laugh:
     
  24. zackesch

    zackesch Member

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    She does that with her glazed stare when I go more into the technical side of things.
     
  25. BrianShaw

    BrianShaw Member

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    Mine too.
     
  26. zackesch

    zackesch Member

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    I put this in my photography field journal. Thanks for the great info.