Do I get this? Flash/Ambient balancing

Discussion in 'Lighting' started by 10speeduk, Sep 2, 2012.

  1. 10speeduk

    10speeduk Subscriber

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    Hi all, I am planning on using off camera flash with my Pentax 67 and buying a meter that can meter for flash.

    Before I commit I want to check that I understand how to balance ambient and flash light to get a nicely exposed shot...

    So say for example the shot is a person on a background outside.

    I measure the ambient light and it is EV7 so at (for arguments sake) F4 the exposure for zone 5 (average) is 1/60

    I then measure the flash on the subject. Say it measures EV9 so (again for arguments sake) at F4 the exposure for zone 5 (average) is 1/250 (2 stops brighter)

    So to balance I would set my camera to 1/60 then set the aperture to F8 (2 stops less light than F4) to balance the flash. Or Shoot at 1/60, F5.6 to give me 1 stop of separation on my subject.

    Is this correct!??

    Thanks in advance wise men!

    Paul

    Also if you can recommend a cheap meter that will do this then fantastic!
     
  2. Steve Smith

    Steve Smith Subscriber

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    As you haven't stated an ISO value, you should use LV rather than EV. EV is purely a function of shutter speed and aperture whereas LV is an actual light level reading. At ISO 100 they are the same numbers.

    I personally do this by setting the camera for the correct ambient exposure then I will us a flash with a built in light sensor such as a Vivitar 285 or 283. The flash will then be put on a setting to give one or two stops less light than needed.

    There are two ways to do this. Either set the ISO on the dial one or two stops lower than the actual film being used or use a setting for an aperture one or two stops more open than actually set on the camera. The Vivitar flash has multiple coloured settings on the dial which make this an easy option. Not all flashes are this versatile.

    Another advantage of the Vivitar is that you can unplug the sensor from the front and connect it with an extension cable so the flash can be away from the camera with the sensor at the camera.

    The wise men can answer properly now.


    Steve.
     
  3. rippo

    rippo Member

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    You should keep in mind that flash exposure has nothing to do with shutter speed and everything to do with aperture. In complete darkness and a manually set flash, f/4 and 1/2 sec will look the same as f/4 and 1/125 sec. As long as you are at or below your camera's flash sync speed, you can ignore shutter speed for flash. Or to look at it another way, use aperture to control overall exposure, and shutter to control the ambient portion.

    I do a lot of on location strobe work, and I'm mixing strobe and ambient all the time. So here's how I go about it:

    First is conceptual...how do I want my subject to appear against the background? If its at the beach near sunset, I'm probably backlighting them with the ambient and then making up the difference with strobe. If it is at a park or perhaps a leafy background, I'm not trying to fight the ambient on the subject, but just change the direction of the light so that it's more pressing.

    So if I'm at the beach, I put the sun to my subjects back and then ask myself: do I want a bright, overexposed background? And do I want a natural look on my subjects faces? Then I'll want my ambient light *on my subjects* to be either +0 or -1. I'll take an incident meter reading at subject position, pointing back to the camera. Let's say it is ISO 400, f/8 at 1/125. If I want barely noticeable flash and super bright background, I'll set my camera exposure to that. If I want a little less background and a little more drama on the faces, I'll set exposure to -1 using the shutter speed (f/8 and 1/250). Then I'll measure the flash component, and adjust the flash power until it reads f/8.

    If I want total drama, I'll set the ambient on the subjects to be -2 and then set a main light and fill lit. Otherwise IMO the shadows on faces can b a bit severe.

    So it's measure ambient first, decide how you want your subjects represented by the ambient, and then adjust flash to create proper exposure. You have to balance things like your camera sync speed: many SLRs can only sync to 1/250 or less, while leaf shutters can sync at any speed (but are limited to 1/500 or so).

    I suggest checking out the strobist.com site for learning off camera lighting. Having a way of seeing your results instantly is a great way to learn. I will often bring a dslr to check my lighting positions before shooting portraits with flash. I don't use it to meter...that's what meters are for. I use it to make sure the face shadows look right before shooting.

    I use a Minolta flash meter. The "IV" I think. It's cheaper that sekonic, which is the de facto standard..
     
  4. RalphLambrecht

    RalphLambrecht Subscriber

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    i usually measure the scene and pick an aperture,the flash by itself would dictate. The shutter speed is irrelevant, aperture priority in a way.
     
  5. polyglot

    polyglot Member

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    For the flash measurement, 1/250 is not relevant. A flash meter tells you ONLY the aperture because the flash duration is (much) shorter than your shutter speed; the only constraint being that if your camera has a focal plane shutter you need to stay under the X-sync speed.

    Like Ralph says, you pick an aperture that's "suitable" for your flash, i.e. places the flash exposure at normal, -1 or whatever, and after that, you select the shutter speed to get the lighting ratio you want. Or you pick a shutter speed due to some other constraint (moving subject, whatever), that tells you the aperture and from there you adjust the flash power.

    A common configuration is sun for "normal" exposure and flash at -1 for fill. Say you're shooting ISO100, a likely combination would be f/11 1/200s exposure (sunny-16 light) and the flash with enough power to illuminate f/8, i.e. one stop less than what your aperture is actually set to. If you wanted the flash and sun to be equal, obviously you'd set the flash power to f/11 but it's going to look bright & flat and if you're shooting chromes then you'll actually be a stop overexposed on any part of the scene that is lit by both sun and flash. If you want more DOF (smaller aperture) with the same lighting balance, you need both a longer exposure and more flash power.

    Aperture affects both flash and ambient, shutter affects only ambient. Flash/subject distance also affects flash power via the inverse square law, so a little bit of moving stuff around can go a long way.
     
  6. Michael W

    Michael W Member

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    You are getting some good answers above.
    I just want to point out that the sync speed of a Pentax 67 is 1/30 so it's not the best camera design for mixing flash and ambient, unless you have one of the leaf shutter lenses.
     
  7. Chan Tran

    Chan Tran Member

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    When you said the flash meter display EV9 there is some problem with that. I don't know if other meters like the Sekonic would take into account of the shutter speed when it displays
    the EV number or not. I use only Minolta meter and with the flashmeter III when set to EV display mode it display the EV number from f/1.0. So if it displays EV9 it means f/22 regardless of the shutter speed. On the flashmeter VI it switches back to aperture display even if you set the meter on EV display mode when you measure flash.
     
  8. markbarendt

    markbarendt Subscriber

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    What the meter tells you is what you get on film.

    In your example, EV7 background vs EV9 subject, the subject will be two stops brighter than the background regardless of the camera settings. (I'm going to assume it is an incident style flash meter.)

    If you want the subject and background lighting to be balanced, the meter needs to read the same EV for both. It really is that simple.

    (This is true of all photography regardless of the lighting source or sources; it is the root fact of the Zone System, BTZS, ...)

    Typically in outdoor photography it is impractical to change the lighting on the background. From your example I'll use EV7 and assume that it is fixed there by mother nature. Also from your example I'll assume that f/4 is the aperture you have chosen to get DOF where you want it and that that means 1/60 is the right time to set the camera to expose the background as you specified you want it pegged to Zone V.

    At this point you are done adjusting the camera, end of story.

    The lighting on your subjects face though may meter at EV5, so too dark.

    To get the subject meter reading up to EV7 (the balanced lighting you want), the flash output needs to be adjusted, not the camera settings.

    If the flash on the first try gives you EV9 on your subject, you need to adjust the flash output or move the flash farthur away from the subject and try again.
     
    Last edited by a moderator: Sep 2, 2012
  9. Maris

    Maris Member

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    Instead of thinking deeply about the problem here's a rote formula I use to get basic 50% fill-flash that works all times all places:

    Incident light flash-meter the subject.
    Note the f-stop reading and set one stop smaller; say for example the flash-meter reading is f8 then set f11 on the lens.
    Then set the shutter speed for correct over-all exposure of the scene at that aperture; for f11 in this example.
    Shoot!

    The result is a correctly exposed over-all scene but the shadows where you originally placed the flash meter are opened nicely from about Zone IV to Zone V, the mid tones move from Zone V to Zone V+1/2, and the higher values scarcely move at all. Most casual viewers accept this photograph as a beautifully lit clear and detailed picture and don't even notice the flash effect.
     
  10. wiltw

    wiltw Subscriber

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    To 'balance' set your shutter and f/stop to the ambient light reading, and dial down the flash power -2EV, and then both sources of light would be same intensity.

    Or you could use f/8 but select 1/15 for shutter speed on ambient, then the ambient intensity equals the flash with no adjustment of flash output at all.
     
  11. Poisson Du Jour

    Poisson Du Jour Member

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    If using a flashmeter (which is always an incident reading type) ie. Sekonic L758D, the ambient/flash balance will be worked out for you based on your selected aperture together with the piddly 1/30 sync of the Pentax 67 / 6x7. A hand-held meter will also provide variation in the balance of ambient/flash in percentage. Sekonic, Minolta AutoMeters, Polaris... there are others, all have their strengths and vices and all can be readily had for good savings on the second-hand market. I bought my L758 for $1080, but it can be obtained now for $400 or so.

    The use of a flash meter is strongly preferable for analysis of ambient/flash to getting bogged down in several levels of figures. It's a simple and stress-free way, but if you're the scientific type, by all means let rip with LVs, EVs, ISOs and whatnot, but your prime consideration should be just to get a picture and inspect the results, not argue about variables. If the first pic doesn't work out, then keep trying. Experience is a great teacher.

    BTW, I would strongly angle for a leaf shutter lens for the 67 (there are two available, but only one still made by Pentax) to enable higher sync speeds and thus greatly more flexibility, but it will depend on what you are photographing and in what conditions.
     
    Last edited by a moderator: Sep 2, 2012
  12. John Koehrer

    John Koehrer Subscriber

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    This is quick and easy. No fiddling around and it works the majority of the time. If you try it you may not bother with the other methods. But if you're trying to work in a set piece situation you WILL need to work a more accurate method.
    I believe the Pentax 67 has a sync speed of 1/30 of a second so any comment regarding ignoring shutter speed should be taken with a grain(or two) of salt. Using a higher shutter speed will fire the flash before the shutter opens.
    Unless you're using one of their leaf shutter lenses.
     
  13. markbarendt

    markbarendt Subscriber

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    The 1/30 sync speed is not great, but not too big a challenge in the situation the OP described with an ambient of EV7.

    As described that situation indicates an EI of 3200, if I did the math right.

    What we don't know is how fancy the OPs flash unit is.

    If it has an automatic mode like Nikon's "A" mode, the flash may be able to adjust its exposure to match the EI and aperture with no extra work.

    If its a studio strobe it can be adjusted to exactly what is needed and tested with the flash meter.

    If its an old flash unit, moving it closer or farther from the subject may be the only choice.
     
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  15. Steve Smith

    Steve Smith Subscriber

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    At EI 3200, EV7 is 1/30 at f2


    Steve.
     
  16. Steve Smith

    Steve Smith Subscriber

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    Then it's using the wrong units as EV (Exposure Value) has to take account of shutter speed and aperture. In fact that's all it is, the level of exposure. It does not take into account the amount of light.

    However, LV (Light Value) is a measure of the light only.

    At ISO 100 the figures are the same.

    In the light meter's defence, it probably does state that all EV readings are for ISO 100 in the instructions but technically, using EV to represent light levels is not correct.

    It's like measuring the length of a brick wall in kilogrammes. Only valid if you know the cross sectional area and the density!


    Steve.
     
  17. RalphLambrecht

    RalphLambrecht Subscriber

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    tha's what i do, but watch to do the later at he same apertureas the former.
     
  18. markbarendt

    markbarendt Subscriber

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    Thanks Steve, I rushed it.
     
  19. hoffy

    hoffy Member

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    I have to admit that this is an interesting conversation and something that I have been considering. I want to possibly under expose the ambient in the examples that I have been considering.

    Would a Thyristor type flash work OK for the fill light? Or would the abundance of ambient light fool the sensor?

    Cheers
     
  20. Steve Smith

    Steve Smith Subscriber

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    Works fine and makes it easier as you don't have to worry about the distance having an effect. Try a Vivitar 285.


    Steve.
     
  21. markbarendt

    markbarendt Subscriber

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    Thyristor type flash units (assuming a modern unit with a sensor) work fine but their sensors face the same challenges any reflective meter faces.

    That can be mitigated with "barn doors" or some other form of shading device used to exclude the background from the sensors view. That's not always needed or beneficial. Many, if not most times, simply pointing the front of the unit at the subject is enough.

    The other wild card is the camera in play. Reasonably modern TTL metered cameras (like a Nikon N90s or F4) with fairly modern lights (say an SB50 which lacks its own sensor) that can talk to the camera and get instructions from the camera on how to fill as the shutter button is pushed.
     
  22. 10speeduk

    10speeduk Subscriber

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    Wow! Thanks for all your answers. To flesh it out, i have a 165mm late leaf shutter lens coming and a minolta Iv flash meter too. I will run through testing with my digital before burning any porta!
     
  23. dpurdy

    dpurdy Subscriber

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    I have used the Pentax 67 many times for outdoor wedding photos mixing flash and daylight. I do exactly as Steve Smith says using a Vivitar 285 and I set the flash to give a stop or stop and a half under exposure and set the camera correctly for the daylight. I have the 9omm leaf shutter and that gives more options for shutter speed but if you are stuck with the 30th you can use a slowish speed film and make it work.
    For a test, regardless of the type of flash metering, I would try setting the flash meter like the film was double the speed it really is and then set the camera ambient meter for the correct film speed. Works for me.

    Dennis
     
  24. markbarendt

    markbarendt Subscriber

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    What kind of flash unit are you using?
     
  25. 10speeduk

    10speeduk Subscriber

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    I have two yn560 units using with cactus v5 triggers.
     
  26. markbarendt

    markbarendt Subscriber

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    So with a quick skim of the manual it seems that your options are like studio strobes, your controls are distance and power level, no auto sensing it seems.

    Thats fun because you will be able to experiment in a very controlled way.

    Trust your meter. If it indicates balanced readings, that's what the film will show.