Educate me on light meters, please.

Discussion in 'Lighting and Hardware' started by DaveAndHolly219, May 2, 2017.

  1. DaveAndHolly219

    DaveAndHolly219 TPF Noob!

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    I’m looking for some advice on choosing a light meter and also how I would go about using a light meter for a specific type of shot that I do a lot of. The basic idea is an outdoor portrait, find the “proper” exposure for the background, and then underexpose that 1-2 stops as my base exposure setting. Then use a speedlight in a softbox to light the subject. I typically shoot wide open or close to it to blow out the background and give my subject some background separation.

    The issue I run into is that with subjects who aren’t particularly patient (kids for example), the time it takes to take test shots and get the flash exposure right can become a problem. I’ve tried TTL instead of manual flash settings, but I usually don’t love the results.

    That’s where I feel like a light meter might come in handy. But the more I think about it . . . how would I use a light meter to help me with this?

    So, in summary:

    1. Would a light meter help me get this type of shot set up/properly lit faster? If so, what would be the procedure?

    2. If a meter would be advantageous for these shots, can I get some recommendations on which one(s) to check out?
    If it matters:

    I use these flashes: Flashpoint Zoom R2
    Triggered by this: Flashpoint R2


    Thank you in advance for any and all input!


     
  2. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    A handheld meter that can do both spot and ambient.

    Use the spot meter to read the background, then the ambient to set the speedlights.
     
  3. Designer

    Designer Been spending a lot of time on here!

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    Given that your aperture is already selected; you would adjust your light to give the proper exposure according to the meter reading.

    Say you had already decided on f/2.8 for instance. Take a meter reading at your subject, and if the reading was say f/5.6, adjust your light to emit less light. When you've got it adjusted to light your subject at f/2.8, you can then take the shot.
     
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  4. DaveAndHolly219

    DaveAndHolly219 TPF Noob!

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    Is there a good resource online, perhaps easily printable that shows how many stops of light are gained/lost by changing from one aperture to another or from one shutter speed to another?

    Let's say I want to shoot at 2.2 and the meter tells me that at my given shutter speed/ISO I need to be at 5.6. I would then need to know how many stops to reduce the flash power. I know that's something I should have memorized, but I don't yet, so a handy chart in my camera bag would be great.

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    Last edited: May 2, 2017
  5. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    One full aperture change (eg f8 - fll or f5.6 -t4) = 1 stop. One stop is one stop whether it is shutter speed, aperture, ISO, or light.

    The way I approach this is as follows: I pre-plan the scene insofar as I know roughly where I intend to place my lights with respect to the subjects and the ambient. I also know about how far away they need to be. I meter the background with my camera using matrix or wide-area metering to give me a good overall average background exposure. You can do with a spot-meter as Sparky suggests, and that's fine for landscape photographers with all the time in the world to take half a dozen or more readings, average highlight/shadow/mid-tones, etc, but I'm lazy. Matrix gets me there in one.

    Knowing that the background is say f8, I will normally set my lights for f8 +1/2 to f8 +2/3 to ensure that it isn't going to overpower the scene. I place my lights where they need to be, ensure that they're set the way I want, pop a test flash, adjust output as necessary, pop a second test flash to confirm and I'm ready to shoot. Total time? <2 min. If you're really slick and stick to a pattern, a common "old school" trick was to attach a piece of string of a specific length to the light stand for each light. Place the light so that the end of the string touches the subject's nose and you're ready to go.
     
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  6. Designer

    Designer Been spending a lot of time on here!

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    I think you could just look at the barrel of your lens and count the stops between f/5.6 to f/2.2 (interpolate). Then adjust your light by the same number of stops, including the partial stop.
     
  7. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    How many lenses these days have f/stops printed on them? :048:
     
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  8. table1349

    table1349 Been spending a lot of time on here!

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  9. Designer

    Designer Been spending a lot of time on here!

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    Maybe he'll have to look at his flash control instead.
     
  10. TCampbell

    TCampbell Been spending a lot of time on here!

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    If you use TTL then you may want to dial in some Flash Exposure Compensation (FEC) to about -2/3rds of a stop to maybe -1 stop.

    A "good" meter will do both spot metering and incident metering as well as support flash metering. A "better" meter will also report "flash contribution" (what percentage of light came from the flash vs. the ambient light).

    I use a Sekonic L-758D series but I see that's now been replaced with their newer L-858D series (the LCD screen is now a color touch-screen). It has a built-in 1º spot meter (reflected metering) for metering points in the distance (landscape photograph to help you find the darkest and brightest point in the scene). It has the incident meter (all hand-held meters generally have an incident meter), it allows you to do averaging (sample lots of points and it'll show you the mid-point as well as the exposure range), it supports flash metering, and it also reports flash-contribution when you use mixed ambient + flash (which is what you want.)

    I generally find I'm pleased with the mixed light results when I get the flash contribution in the 30% to 50% range. This is a nice fill range where it won't look noticeably like a flash was used, but you'll get rid of harsh shadows.

    The Sekonic L-478 is the mid-range model and it does much of what the 858 can do ... but it doesn't have a built-in spot meter. You can buy a 5º reflected meter accessory (not as pin-point as a 1º meter). But it does report flash contribution.

    Sekonic's high-end meters allow you to "profile" the camera. This is an optional accessory (exposure card & software) that is used to test the range of your camera, build a profile, and then install it into the meter so the meter can warn you if a scene requires more range than the camera can handle in a single exposure.
     
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  11. TCampbell

    TCampbell Been spending a lot of time on here!

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    Most cameras use 1/3rd stop increments. Each "click" on your dial (aperture or shutter speed) is 1/3rd stop. So you could count the clicks. (Just be aware that many meters will read in 1/10th stop increments - but good meters let you adjust that - and also some cameras let you adjust it as well. So it's not guaranteed to be 1/3rd stop, but that's the most likely.)

    A full stop of aperture either doubles or halves the exposure. And so it is with cutting the power on a flash... you get 1/1 (full), then 1/2, 1/4, 1.8, 1/16, and so on where each setting cuts the light output in half (so the flash is adjusted typically in whole stops ... not 1/3rd stops). This means when you determine how much aperture change you made, you'll need to round any 1/3rd stops to the nearest whole stop and that way the amount of light will still be within 1/3rd of a stop ... which is enough to be noticeable, but not enough to be harmful to your result (it'll be really close to what you want and if you really wanted to fuss it would be very easy to tweak in post processing.)

    Aperture numbers are based on the powers of the square root of 2.

    Any number raised to the 0 power is 1.
    (√2)^0 = 1
    (√2)^1 = 1.4
    (√2)^2 = 2
    (√2)^3 = 2.8
    (√2)^4 = 4
    (√2)^5 = 5.6* (really 5.7)
    (√2)^6 = 8
    (√2)^7 = 11
    (√2)^8 = 16
    (√2)^9 = 22* (really 23)
    etc.

    The reason it's all based on the square root of 2 is because anytime you increase (or decrease) the diameter of a circle (in this case the circle is your aperture opening) by a factor equal to the square root of 2 then you EXACTLY double (or halve if decreasing) the area of that circle (or in our case the amount of light that can pass through).

    You could find the 1/3rd stop values by using 1.33, 1.67 between the whole number of 1 & 2 -- for example.

    BTW, the one confusing number in the table is f/5.6 and 22. If you do the math, the square root of 2 raised to the 5th power is 5.6568... so based on rules of rounding, that would be rounded to 5.7 -- not 5.6. For some reason we use 5.6 (whoever established the standard rounded down and violated the rules of rounding... but ONLY on that particular f-stop.

    But another pattern you might notice is that every 2nd value on the table is doubled. e.g. 1, 2, 4, 8, 16 & 32. And the values in between are also doubles... 1.4, 2.8, 5.6, 11 (ok that's rounded down from 11.2) but then 22, & 44. So my guess is they did it for simplicity of memorization. They also likely rounded the square root of 2 to simply "1.4" instead of 1.41421.... But in defense of that... the difference in the rounding errors isn't enough to be noticeable in an exposure. You can safely disregard it since the difference is too insignificant.
     
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  12. epatsellis

    epatsellis TPF Noob!

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    Something I make a point of teaching everyone that I mentor, when balancing available light and strobes, shutter speed and aperture affect ambient exposure, only aperture affects strobe exposure. It becomes trivial to meter in camera, in manual, then stop down 2-3 stops of shutter speed (staying below max sync speed, obviously) then fire a TTL strobe and your flash exposure will be correct, and you background darker by how ever many stops you chose... Harder to explain than do once you practice. I'm all for having a good light meter (and I own at least a dozen really nice ones.), but practically determining an expedient method that doesn't require you to move your eye from the viewfinder is essential. Worked back in the film days and really hasn't changed one bit today. Most cameras can be set to vary in 1/2 or 1/3 stop intervals, at least all the Nikons I have allow you to.


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