Reconciling Flash Output Using Different Brands

Discussion in 'Beyond the Basics' started by ElizaMM, Jan 23, 2019.

  1. ElizaMM

    ElizaMM TPF Noob!

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    I have a Canon 430EXII, GN 43/141, ISO 100 and an Andooer560 IV, GN 50, ISO 100. Is there a way to figure out the necessary power on the Andooer for fill flash, without trial & error? For example, say I want to set the Andooer (fill) to 1/16 of the current power of the Canon (main). Hit & miss (my main MO) works, but is time consuming. With both at 1/1 and 1/1, the Andooer seems a fair bit brighter.


     
  2. smoke665

    smoke665 TPF Supporters Supporting Member

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  3. Designer

    Designer Been spending a lot of time on here!

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    You could figure this using math. Make a fractional relationship between the two guide numbers (GN), and then use that relationship to reduce the power setting of the Andooer, or increase the power setting of the Canon.

    (43/50) Canon = Andooer
     
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  4. ac12

    ac12 No longer a newbie, moving up!

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    Determine (by trial and error) the TRUE guide number for both flashes.
    And verify the power settings. Is 1/4 power really 1/4 power?
    Once you have that, you can determine your ratios.
     
  5. ElizaMM

    ElizaMM TPF Noob!

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    Thanks for the suggestions. Finally tried someone else's incident meter. It does take the guess work out of the equation.
     
  6. TCampbell

    TCampbell Been spending a lot of time on here!

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    Light falloff means that the distance the flash is from the subject will cause the light to appear dimmer the farther the subject is ... based on the square of the distance from the light source.

    A "guide number" means that the flash is capable of properly illuminating a subject at that distance (most are now in meters but some are listed in feet) IF the camera is at ISO 100 AND the lens is at f/1.0 and the flash fires at full power. Obviously the lens wont be at f/1.0 but that baseline is used because you can determine the coverage by simply dividing the guide number by the f-stop (and this only works when the base f-stop for the Guide Number is f/1.0).

    In other words if you shoot a subject at f/5.6 then you'd divide the guide number of 43 meters by 5.6 to get about 7.7 meters (or about 25 feet).

    Keep in mind that 430EX II has a reflector that adjusts forward backward to compensate for lens focal length (if using a wider lens, you want a wider scatter of light. If using a longer lens, you want a narrower scatter of light. The 43 meters GN assumes the beam was narrow (long focal length).

    Often you don't actually want them to provide equal illumination. Usually one is set to purposely deliver less light and this creates some directionality to the light without harsh shadows. While there are many styles of lighting ... typically a main light is off to the side ... perhaps at a 45° angle to the subject (relative to camera position to the subject) and then a smaller/weaker light is either positioned with the camera *or* perhaps on the opposite side. This provides some directionally which creates a better sense of depth (subject appears more three-dimensional and less "flat").

    Pickup a copy of "Light Science & Magic".
     
  7. WayneF

    WayneF No longer a newbie, moving up!

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    The 1/16 power seems surprising. If the flashes were equal power and at equal distance from subject, that 1/16 would be 4 EV less, and you probably would not notice it was even present. So the situations definitely cannot be equal flashes.

    The Andoer says it is Guide Number 50. It does not specify feet or meters, but guessing it is Chinese would make it meters.

    I am guessing that its flash head does not zoom? Specs don't mention zoom, and doesn't say what focal length lens it covers, perhaps that is in its manual? 24 mm full frame would be common minimum for speedlights, but GN 50 (meters) would be about half again more powerful flash than is commonly normal for that. That doesn't really matter if it does not zoom, then it would simply always be the GN 50 spec. If it does zoom, then that number would apply to some one zoom value, which is surely specified somewhere to have any meaning.

    Your question about Using the Guide Numbers:

    The Canon 430 EXII flash has different guide numbers for each different zoom and power level, specified in a Guide Number Chart in its manual (page 36), which says full power is GN 25 (meters) at 24 mm zoom, up to GN 43 at 105 mm zoom. So it is a weaker flash. GN 24 compares to GN 50 as 2.1 EV less power.

    The power levels sure sounds like the Andoer should be the main light, and the Canon the fill.

    Going further, the Guide Number calculator linked at Understanding Camera Flash Guide Numbers, plus GN Calculator recomputes GN at different power levels. If the Andoer is entered there as GN 50 at ISO 100, it can say this is:

    GN 50 (meters) at Full power
    GN 35.4 at 1/2 power
    GN 25 at 1/4 power
    GN 17.7 at 1/8 power
    GN 12.5 at 1/16 power
    And it can compute third stops of power too.

    That works for the Canon too, but the Guide Number chart already shows reduced power level guide numbers for each zoom setting.

    So if the lights were at the SAME distance, and had the SAME (or none) lighting modifiers added on the flash head, i.e., equal flash situations, then from the GN chart in the Canon manual, you could find its equivalent guide number AT THE ZOOM AND POWER you have it set to.

    The same Guide Number calculator has a GN comparison calculator towards page bottom that gives EV difference of two GN (at same zoom and ISO and modifiers, etc). But if GN were made equal, then power reduction can do it too, each half power step down is 1 EV less.

    Or if the distance to subject of both were the same (and same modifiers, equal situations), you could determine corresponding settings (zoom and power level) to match the Andoer at its setting you choose.

    If distances were not the same, you can account for it by placing EQUAL lights at distances corresponding to f/stops.
    For example, equal lights placed at 2 meters and 2.8 meters will be 1 EV different, and 2 and 4 meters 2 EV different (the closer flash is the brighter). Distances in feet work exactly the same, 2 and 2.8 feet, or 2 and 4 feet, etc.

    Assuming all guide numbers are reasonably accurate, normally a lighting ratio of fill at 1 EV less than main is pretty proper for color portraits, esp of women or children. Old rugged cowboy men might use fill 2 EV down. Or grayscale B&W photos can use a bit more too.

    You can test GN accuracy by simply using it to take a test picture. GN 50 means f/10 at 5 meters (or f/5 at 10 meters, or any other combination multiplying to GN 50) should be properly exposed (direct flash, no modifiers). If it is properly exposed, then the GN is reasonably accurate. But actually measure the distance, and only decide "proper" from a few photos in different scene situations, not from only one quick try. Or you could verify it with an incident meter.

    An incident meter sure makes setting up multiple flash easy, fast, repeatable, and sure in studio situations.
     
    Last edited: Feb 8, 2019
  8. ElizaMM

    ElizaMM TPF Noob!

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    Thank you all. I have printed this page for studying.
     

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