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How do you balance flash & ambient light

Discussion in 'General flash photography, lighting, and technique' started by Debbie H, Jul 24, 2008.

  1. Debbie H

    Debbie H

    Aug 23, 2007
    I think I know a little about this subject but I know that there a lot of you that know a lot more than I.
    If anyone can really explain in "Simple detailed terms" how do you balance Flash and ambient light? I know you have two exposures one for the ambient light and another for the flash and I know it has to do with the shutter speed. Where do you begin to know how to balance the two so you will have a good exposure of both??? Would really appreciate some help with this subject and really understand it better. Thanks so very much!! Debbie
  2. Hi Debbie, I have recommended this before to you but will say it again, if you will do what the tutorial says you will understand how to do this. I literally did mean that you should shut out all distractions and do the steps over and over until the light comes on and you understand what controls what. I know you have the basics and you just need to gain confidence in what you already know. Practice makes perfect. Good luck.

    Basically the flash takes place in micro seconds so SS has no effect on it. SS controls the ambient light. Flash power can be adjusted up or down on the flash and also can be controlled with aperature. Flash weakens as you move it away from the subject and strengthens as you move it towards the subject. This is especially important to know when you have your flash off camera and triggered wirelessly. Your on camera commander or SU800 can trigger the flash remotely from significant distances (up to 50 feet). When using flash SS is limited by the sync speed of the camera, normally around 1/250 of a second. When shooting outside in bright sunlight this sync limit makes it difficult to control the ambient light with the SS so you may need to have an ND filter and/or use a small aperature. You can exceed the sync speed of the camera by going to FP (high speed sync) and then can shoot at much higher shutter speeds. The tradeoff is that your flash power is very much curtailed by this setting.
  3. rsprouse


    Jan 25, 2006
    Encinitas CA
    Hi Debbie:

    You have it right - think of the ambient exposure and the flash exposure separately. The ambient exposure is affected by ISO, aperture, available light intensity and shutter speed. The flash exposure is affected by ISO, aperture and flash intensity - the shutter speed has essentially no affect, as long as you are at or below the maximum sync speed of your camera.

    How to balance the two exposures is a creative decision. If you just want a little fill flash on your subject, set the ambient exposure as you would for a shot without flash, and then pump in a small amount of flash. How much flash depends upon several factors - how far away the flash is from the subject, what kind of modifier you might be using (diffuser, umbrella, etc.) and of course the amount of fill you desire. You might find it helpful and informative to literally shoot first without the flash, and adjust things until you get an acceptable exposure. Then turn on the flash and take a guess at the power setting, maybe starting a 1/8 power, for example. Then, based upon the result, dial the flash power up or down until you get the balance you desire.

    In some cases you might want the flash to have a stronger effect, providing more than just a slight fill. This allows you to tone down bright and busy backgrounds, for example. The principle is the same - set up an ambient exposure first, at the desired exposure level. In this situation, however, you may want the ambient exposure to be one to two stops underexposed (or even more). So again, shoot a test shot that gives you the desired tonality, knowing that the subject will be underexposed. Once you have an exposure that gives you the desired tonality of the background, then turn on the flash and pump in the desired amount of light, which will of course be higher than what you would use for a gentle fill.

    Does this help? With enough practice you will be able to do this fairly quickly, with fewer test shots, because your guesses will be closer based upon your experience.

    -- Russ

  4. Trust us--the light will come on!!!!! (I couldn't resist that!:biggrin:) .
  5. Bingo. :887:
  6. jfrancis


    May 8, 2005
    Orlando, FL
    All great advice. I would go one step further and advocate that to really understand this stuff, you should first get comfortable shooting in manual exposure mode. Once there, pick an aperture based on the DOF that you want. Now, meter the background and adjust your SS to get the correct exposure. Leave your SB600/800 in TTL. Take a shot. Next, vary the SS up or down from its starting point and note the effect on the image. You will quickly see that your subject illumination stays the same, while the level of ambient light goes up or down. Practice this exercise for a few days and your flash ability will be vastly improved. To be honest, this is the lesson that I bet 90% of photographers that use flash never learn.

    One other thing - get comfortable with using FV lock.
  7. Outdoors , put your flash on TTL/BL , take a few test shots and adjust -flash compensation if needed . Indoors I agree about getting used to manual . Start with iso 400 , f5.6 1/30th sec , take a shot and see if you have enough ambient and adjust till you have some of the inside light showing . Then add the flash on TTL mode , bounced off the ceiling if possible and see how it looks .
    The dummy method is to set your flash to "slow synch" and then the camera will expose as it normally does and add the flash . the trouble with using ''auto'' type methods on the camera is that you have to remember the ev compensation directly affects flash .
    If you decide to adjust the ev to -2 indoors to look more natural the flash will also back off to -2 and you will have to dial in +1 [ the maximum it can go I think ] which will mean your flash is firing at -1 effectively [ -2+1 ] .
    Outdoors isn't too easy to mess up , indoors when you turn on flash the camera sometimes drops to the lowest speed you allow , normally 1/60th but you can set that lower , like 1/15th to catch the ambient while the flash freezes the movement .

    I had an opportunity to do some tests myself at a recent get-together .

    I took a test shot on auto [ f3.5 , iso1600 , 1/60 th ] to see what the camera chose as a normal exposure and then backed it off a bit to get a more realistic exposure .

    Subscribe to see EXIF info for this image (if available)

    I chose 1/30th , F5.6 , iso800 to catch some ambient , then I did a direct flash for comparison .

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    And then the same settings with bounce flash from my little SB400/D40 combination .

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  8. Debbie H

    Debbie H

    Aug 23, 2007
    Yes I do remember Gordon and I did read it:smile:. I guess at that time I didn't see how important that information really was. :eek:  I do now!!! I just printed it and I'm going to study it. So a lot of times when it is darker like in a reception hall, if you want more ambient light or a lighter background you might have to put your camera on a tripod to get the shot if the shutter for the ambient light is 1/15 or 1/30? I have tried this at a slow shutter with flash and I'm still coming out with a blurry picture. I can hold it a 1/60 with flash, but that is as good as it gets.

    Yes it does help Russ!! Thanks so much for taking the time to type all that out for me! Debbie:smile:
  9. jfrancis


    May 8, 2005
    Orlando, FL
    That's when increasing your ISO is also a valuable option.
  10. Debbie H

    Debbie H

    Aug 23, 2007
  11. Debbie H

    Debbie H

    Aug 23, 2007
    Yes your right John!! And the D300 does help with higher ISO settings. :smile: Thanks for the info. Debbie
  12. Debbie, keep in mind that in a darkened environment at a slow shutter speed it is the ambient light that is causing the blur. If it were completely dark the flash would freeze the movement no matter what your shutter speed but if there is ambient light and you set your SS to 1/30 or slower you are bound to get motion blur. This can be from people movment or more likely camera shake. As has been pointed out you simply move your ISO to a higher number and then reset your SS and retake. Another option is to use a tripod to eliminate camera shake but then you still have to contend with people movment. The higher ISO is the best option.

    One other thing, if you look at the middle image posted by Desmond above you will see the inverse square law of lighting come into play. The inverse square law says that if you double the distance from flash to subject (say 5 ft. to 10 ft.) the power of your flash drops to 1/4. It is easy to see the fall off of light from front to back. When he used bounce flash the lighting was more even because the distance from ceiling to subjects remained fairly constant. This is also another reason for raising your ISO so that the ambient light can play a bigger role in your exposure and the flash simply acts as a fill.
  13. Debbie H

    Debbie H

    Aug 23, 2007
    Thanks Gordon!! Once again!!:redface: I didn't know that.:wink: Gosh I learn something new everyday. I guess I will be raising the ISO. It seems like I'm getting closer everyday, meaning learning more about photography. Just got out Understanding Exposure by Bryan Peterson yesterday and read that again. Well more practice to do today. Debbie:smile:
  14. I read this advice being given all the time, but don't understand what TTL/BL is all about.

    According to the sb800 manual, when in TTL/BL mode, "the flash output level is automatically adjusted for a well balanced exposure of the main subject and background". But the flash doesn't illuminate the background, so how can it effect its exposure? It doesn't appear to change the shutter speed, iso, or aperture, which I'd think would be the only ways to effect the exposure of the background.

    When I'm shooting flash outdoors, I take control of the background exposure by selecting the shutter speed, aperture, and iso, so I thought the only job left for the flash would be to expose the subject properly, which it TTL.

    Would you mind explaining how TTL/BL works?
  15. Frank, I think that in P/S/A mode with TTL/BL the camera sets the exposure for the overall scene and then adjusts the flash automatically to give the best exposure to the subject. The problem is it expects the subject to be in the center and if it is off to one side or the other it does not do all that great. There are ways to overcome that but personally I like to shoot in M with TTL as that way I am in control and have no one to blame but myself if I am off.

    I will be interested to hear what Desmond has to say.
  16. dan1son


    Sep 24, 2007
    The idea is that it uses the rest of the exposure meter (in Matrix or Center Weighted) to attempt to do exactly what you do manually. It meters the scene without flash, decides on an exposure, then fires the flash to fill in the subject. That's why it won't work on spot metering.

    You can usually overcome the off center part by using fv-lock. Meter for flash in the center, then recompose and shoot. Works pretty well and is faster for changing environments then shooting manual.

  17. Thanks for the inputs, Gordon and Dan. I just did some experimenting, and have learned something new :biggrin:.

    Gordon, ttl/bl appears to work in manual mode, too.

    Dan, ttl/bl doesn't appear to effect shutter speed, aperture, or iso, but it does adjust the flash to keep it from overpowering the subject. I think it may just subtract the background from the equation when it computes the power for proper exposure of the foreground.
  18. Frank, I assume you mean it does not affect SS, Aperature, or ISO in M mode? It for sure affects them in P/A/S mode. The difference would be that in M mode you are setting the above manually.

    I have never used TTL/BL in M mode but it would be worth experimenting with, thanks. I am aware that it does not work with spot metering.
  19. I'm not sure of that, Gordon. Using aperture priority mode, I shot the same scene in in TTL and TTL/BL, and there was no difference in SS, aperture, or iso. All it did was turn down the flash power.

    I'll be interested in your test results.
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