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Thread: Understanding Incident Metering

  1. #41

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    Re: Understanding Incident Metering

    Quote Originally Posted by Pere Casals View Post
    My guess is that manufacturers follow the ISO recommendation that specifies a range, so the we have that 1/6 EV differences between meters, so they are in fact aiming a 16% to 18% reflectance.





    You are right, this comes from the ASA PH2.5-1960 speed change.

    In 1960 Box Speed was doubled without any film manufacturing change, so in theory the Zone System experimented a shift.

    Divine ZS inspiration came to AA while shooting the Half Dome with an Adon, this was 1927, 33 years later ASA changed the 20x to 10x.


    Anyway IMHO it can be debated if we should or not rate film at its half speed to use the ZS, now we have accurate meters and we don't need that additional safety factor of one stop that was removed in 1960.

    AA says Z-II is "Textured black; the darkest part of the image in which slight detail is recorded". Z-II is -3 stops in the meter, so outside the toe if using the post 1960 box speed.


    My view is that ZS is not a recipe but a methodology & visualization and we need to ajust it to our process, depending on how we meter and develop we have an impact, so IMHO at the end we just need to consider a personal ISO for a film that makes our Z-II "the darkest part of the image in which slight detail is recorded".

    This is what I personally concluded...
    This is a well-considered conclusion.

    I’ll state as fact manufacturers do not consider any gray card percentage in their calibration. As casual experimenters, we are interested in gray card percentage, with 18% the most easily obtained for our experiments.

    They don’t deliberately relate, but we might discover a relationship, or theorize about a relationship we can test.

    I have a Sekonic gray card with 1/6 stop differences between a set of seven chips that span one f/stop. That gray card is good for tests like this.

    For example I could shoot this card in a scene that I photograph according to careful metering, with incident dome or with flat disc, with reflective light mode. I could hold the card correctly and I could position it wrong.

    The results could be compared easily by finding the chip that placed 10x the speed point... And that would be the deduced gray card percentage which exactly matches the exposure meter.

    In a practical outcome from this test, we could write “scenarios” - in it we could talk about how we positioned the card, what meter was used and then the usable information...

    How much to adjust a reading that was taken with an 18% gray card.

    (Sounds like we intend to write some instructions which will be like the Kodak instructions, doesn’t it?)

  2. #42

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    Re: Understanding Incident Metering

    Quote Originally Posted by Bill Burk View Post

    (Sounds like we intend to write some instructions which will be like the Kodak instructions, doesn’t it?)
    Yes, a bit !

    The test you propose would be interesting to be performed...

  3. #43
    Indiana, USA chassis's Avatar
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    Re: Understanding Incident Metering

    This image was made on July 5, and was metered with both incident and spot with a Sekonic L-758DR. Setting sun (golden hour) was to camera rear. Camera to subject distance was approximately 50 feet/15 meters. f/45 was chosen with ISO 100 for Kodak Ektar 100. Spot metering on the shadows in the cornstalks gave 1/2 second exposure, and from memory the sky was 3 stops brighter, again using spot metering. Incident metering from the camera position with the dome facing the sun gave 1/4 second exposure. The sun was fully exposed, no clouds were diffusing its light.

    I set the shutter to 1/4 second, and made the exposure.

    I'm satisfied with the result. Overall brightness of the image could be higher, but that is a postprocessing choice, not the exposure. There is more than enough density on the negative. For my aesthetic, "black" is an acceptable color, and often occurs in the shadows.


  4. #44

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    Re: Understanding Incident Metering

    Quote Originally Posted by chassis View Post
    the sky was 3 stops brighter
    Excellent example !

    One thing I found with saturated subjects with color film is that while a spot reading may look moderately overexposed it can happen that the amount of light of the saturated color may overexpose a lot one of the channels.

    This effect is seen well in the 3-color histograms in the DSLRs.

    One interesting feature of the Nikon F5 is that its photometer is RGB, beyond the 1k points, the smart neural network and the DX code informing the system about film latitude, the RGB information allows the camera to not overexpose a particular color channel.

    I think this is an issue when shooting Velvia if not wanting a washed sky... Negative film is more bullet proof.

    The F5 (and 6) is an excellent LF photometer, if not considering weight

  5. #45
    Alan Klein's Avatar
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    Re: Understanding Incident Metering

    Quote Originally Posted by Pere Casals View Post
    It should deliver a good exposure for normal conditions. The Problem with incident metering is when not all the scene is bathed with the same incident light, then may take more readings to decide what you over/under expose.

    Also while with spot metering you know what over/under exposure you have in each spot of the scene, with incident metering (when illumination is challenging) you have to guess how the deep shadows and highlights will be, and particular film toe/shoulder has an impact.

    One thing it can be done is shooting a 35mm test roll of the same film you use for LF. You just select some meaningful scenes to make bracketings, and taking notes of the incident metering, the SLR metering in matrix, ponderated and spot modes, with the spot readings of highlights and shadows. This would give you a solid criterion about when you should modify the indicent metering to suit your visualization, from the results you bracketed.
    Well, I have to admit that when shooting (MF 6x7 120 roll film), I cheat by bracketing +1 and -1 stop with Velvia 50 and with Tmax 100. SInce I'm shooting landscapes, this works for me. And roll film makes it simple to do and relatively cheap assurance I get at least one good exposure. I think on the BW film I probably should bracket -1 and +2.

  6. #46

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    Re: Understanding Incident Metering

    Quote Originally Posted by chassis View Post
    This image was made on July 5, and was metered with both incident and spot with a Sekonic L-758DR. Setting sun (golden hour) was to camera rear. Camera to subject distance was approximately 50 feet/15 meters. f/45 was chosen with ISO 100 for Kodak Ektar 100. Spot metering on the shadows in the cornstalks gave 1/2 second exposure, and from memory the sky was 3 stops brighter, again using spot metering. Incident metering from the camera position with the dome facing the sun gave 1/4 second exposure. The sun was fully exposed, no clouds were diffusing its light.

    I set the shutter to 1/4 second, and made the exposure.

    I'm satisfied with the result. Overall brightness of the image could be higher, but that is a postprocessing choice, not the exposure. There is more than enough density on the negative. For my aesthetic, "black" is an acceptable color, and often occurs in the shadows.

    Maybe someone can explain these numbers to me. I the spot metre reading of the " the shadows in the cornstalks ' which are black, is a reading of 1/2 second; and the shot was at 1/4 second, does this not place the shadows in the cornstalks in zone 4, one down from 5? How can they be so black, like zone 2?
    Regards
    Bill
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

  7. #47

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    Re: Understanding Incident Metering

    Quote Originally Posted by cowanw View Post
    Maybe someone can explain these numbers to me. I the spot metre reading of the " the shadows in the cornstalks ' which are black, is a reading of 1/2 second; and the shot was at 1/4 second, does this not place the shadows in the cornstalks in zone 4, one down from 5? How can they be so black, like zone 2?
    Regards
    It is obvious, that Sekonic has 1º cone, reading was at some 15m, this is (15000 x Sin(1º) x 2) so the metering spot diameter is 524mm, it not only takes the dark shadows but also the plants:

    Click image for larger version. 

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  8. #48
    Indiana, USA chassis's Avatar
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    Re: Understanding Incident Metering

    Quote Originally Posted by Pere Casals View Post
    It is obvious, that Sekonic has 1º cone, reading was at some 15m, this is (15000 x Sin(1º) x 2) so the metering spot diameter is 524mm, it not only takes the dark shadows but also the plants:

    Click image for larger version. 

Name:	p2955794824-4.jpg 
Views:	19 
Size:	51.3 KB 
ID:	180284
    Pere, yes you are correct.

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