Studio Lighting Question

Discussion in 'Beyond the Basics' started by smoke665, Mar 13, 2018.

  1. smoke665

    smoke665 TPF Supporters Supporting Member

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    Reading Jeff Smith's "Guide to Head and Shoulders Portrait Photography". He talks about the output of the background light being a function the the main and the fill. That adjusting the background equal to the main and fill will render the background as the eye would see it under normal light. However he doesn't tell how to calculate the total output. Maybe I'm over thinking it and it's just a matter of a meter reading firing both strobes, or is there another way to combine the output of both?


     
  2. Derrel

    Derrel Mr. Rain Cloud

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    He's not telling you "how" to meter the background light!! Jeeze, not very responsible of him to write that and not clarify. Not much time here before I head off to work this early AM. You meter the subject with the incident dome, but must read the background's value from camera position with a reflected light meter, to determine how much light it has; this was systematized years ago by Dean Collins...see his videos on YouTube...chromazones is the spelling he used, as I recall. One can determines the background brightness of the backgound (black,white,gray,etc.) or its color value (light red, or pink, for example from the same exact gel used) by the differential between incident (subject) reading and exposure used, and the amount of background light that reflects back to the camera.

    Incident metering for the subject on the stool, reflected reading from camera position, that determines how the brightness/color value of the background will appear. This will also take into account any light from the key or fill that hits the background, and is the correct way to meter. One can ___NOT___ use an incident background reading to determine the bg density.
     
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  3. smoke665

    smoke665 TPF Supporters Supporting Member

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    Thanks, I'll check out that video. Hate to admit it but I've always used the trial and error method on the background. Would be nice to be able to dial in with some measure of reliability, especially as I am going to multiple light setups.
     
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  4. Derrel

    Derrel Mr. Rain Cloud

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    I learned a lot of my studio lighting knowledge from Dean's "Finelight" video series back in the 1980's and 1990's.

    This is the Chromazones video; it has a mere 339 views right now! SUCH a shame. Dean Collins was a master educator; his work has been,sort of, taken over by Tony Corbell, who was an assistant to him 30-plus years ago.



    About two minutes into this, you'll hear some numbers, "2 and 1/3 stops above 18% gray is photographic white, while 4 and 1/3 stops reflective below 18% gray is photographic black".

    "Whatever our camera is set at....the subject's diffused value....the background is 4 and 1/3 stops reflective from what we're shooting at....the background is photographic black."

    "it's a system, an empirical system...a system relying or based solely on observation...experimentation..and documentation."
     
  5. smoke665

    smoke665 TPF Supporters Supporting Member

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    Interesting, thanks for sharing. I've watched it twice now and there's still some fog floating around in the brain. Maybe some clarification.
    • If I meter a "reflective reading" off my subject of f/11, and adjust my background light to read a "reflective reading" of f/11 then the background will render as 18% gray regardless of if the background is black or gray. Is this correct?
    • If I meter a "reflective reading" off my subject of f/11, and adjust my background light to read a "reflective reading" of f/25 (+21/3)then the background will render as white, or f/2.4 (-41/3) then the background will render black. Is that correct?? Or am I reversed? Not sure if I'm coming or going now??? LOL
    • He lost me when he talked about adjusting the aperture rather than light to achieve this, as wouldn't that also affect the subject?
     
  6. Derrel

    Derrel Mr. Rain Cloud

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    The idea is this: you set the camera's exposure to set the diffuse highlight value of a subject; with digital positive medium and a caucasian-skin-toned person, this is pretty close to a direct, un-compensated, incident light reading. So, meter the subject using the incident light meter, and set that exposure on the camera.

    NOW....using _____ANY_____ color of background paper, wall, or canvas, you can determine the density/color/value of the background by using a ____reflected____ light meter reading made from the camera position.

    If you have a white piece of paper as the background in the studio, it takes very little light to ensure that it renders as white;

    If you have a gray seamless paper, you'll need MORE reflected light making it back to the camera sensor to render as white;

    If your seamless backdrop is BLACK velvet, it needs to have a LOT of light blasting at it, so that the light that comes back to the camera sensor drives the black up to render as white.

    The system is based on setting the diffuse highlight by metering the main and fill lights, and any other lights that are on, using an incident meter reading, not a reflected reading and setting that exposure level on the camera....a black car and a white car will have hugely differing reflectance values, so that's not the way this system is set up.

    The light that actually makes it back to the sensor or film...from the background, MUST be metered at camera distance; one could meter using the incident meter's hemispherical dome, measured at the background, but a white, a gray, and a black backdrop would ALL have the same "incident" value, but the reflected values would be wildly different.

    This is the part you're missing out on understanding: incident meter's reading = the actual exposure set on the lens for the subject, in f/stop value. Reflected light meter's reading froim the CAMERA distance!!!!; this reading is used to determine how much more, or less, light is actually hitting the sensor or the film, using _ANY_ color of backdrop paper, and the difference in this reading from that of the exposure used on the lens, determines how bright or dark said background will be rendered. That's why he specifically mentions the reflected meter reading's differential from the diffuse highlight value, which is what he calls the exposure setting's f/stop.

    The white and black values he mentions are the degree of difference (in f/stops) in a reflected light meter's reading when that reading is made from camera position,and he expressed white, and gray, and black background values, in f/stop difference from f/stop the lens is set to.

    Using incident metering on the subject is the basic idea as to how to set the lens's f/stop for the main and fill light set-up in use. Then, to determine if the background is white,or gray, or black, regardless of the actual reflectance value of the paper or canvas or wall, then the "differential between the exposure, and the quantity of reflected light that hits the sensor" becomes the way one can predict the value/color/hue of the background that is rendered in the final picture.

    There are actually two exposure values that must be considered: one Exposure Value for the subject..and an Exposure Value for the amount light that strikes the background and which actually travels allllll the way back to the camera. Keep in mind that the background and the subject might be 5,10,15,20 feet different from one another, PLUS there's the distance from the background paper and then the distance from there and back to the camera, and there's a range of background reflecting ability that tremendously affects the "brightness" of the backdrop in the final picture...this is why the background density MUST be measured, by a reflected meter, at the CAMERA position.
     
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  7. Derrel

    Derrel Mr. Rain Cloud

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    Here's a modern imitation of Dean Collin's "chromazones" color density/saturation, based on the degree of ____difference____ of the ____reflected light readings___ off of a background. So....using the SAME subject exposure, let just say f/11, when the background reads a strong "minus" exposure level compared to the subject's exposure value, then the color is very dark and saturated; when the reflected light meter reading is much "brighter" than the subject's exposure setting (still, f/11), then the colors are lighter, and more-pastel.

    By using this system, this empirical system, one can use white, or gray,or black seamless paper, and can get _identical_ background colors, despite the huge degree of difference between how much light white paper,and gray paper, and black paper reflect.

    Back in the days of $1.50 per sheet of 4x5 film, and $3.00 per sheet of processing for E-6, this system was invaluable. It's still hugely useful. Speedotron's Brown Line power pack flash distribution allows me to drive gray paper up to pure white by putting more light on the paper and less light on the subject. White paper can be brought "down" to gray by not having much light hit it and make it back to the camera; if you need to make white paper into a very,very dark gray, you can move it quite far back. But the light that HITS the backdrop paper does NOT equal how much light travels back to the camera sensor, and that's why we must meter that at camera position, using the reflected light meter.

    Chromazones, try 1b
     
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  8. smoke665

    smoke665 TPF Supporters Supporting Member

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    Okay I missed this part. I thought he was saying "reflected" on both background and subject. Makes more sense now. Need to set up the lights and practice with this a bit.
     
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  9. Dave442

    Dave442 No longer a newbie, moving up!

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    Nice summary Derrell. I also heard "reflected" in the video, only having read your explanation first I knew what he was talking about.
     
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  10. ac12

    ac12 No longer a newbie, moving up!

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    From a practical POV, I think it is difficult to take a reflected flash reading off a subject's face. Skin tone and makeup will change the reflectivity of the skin. Plus you, your hand and meter in front of the subject, may block some of the light from the flash. It is much easier to take an incident flash reading, at subjects position where you are not shadowing the meter.

    The Speedotron Brownline packs that I have, have fixed power distribution ratios. I have to check what the Blackline packs can do. So with the Brownline, I could not adjust the background illumination level easily. Here is the disadvantage of a pack unit where you cannot easily control the power levels to the individual heads, vs. a monolight. I will have to play with this. I like the idea, I just have to figure out how to make it work. But first, I need to clear my garage.
     
  11. ac12

    ac12 No longer a newbie, moving up!

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    Derrel,
    With reflected metering, why do you have to meter from camera position?
    I thought with reflected, it would not mater, or matter very little.
    Time to go play with my spot meter.
     
  12. smoke665

    smoke665 TPF Supporters Supporting Member

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    I'm still muddling through this, but I assume it would have to do at least partly with the angle of incidence on the background lights?
     

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