Balancing Flash and Ambient Light Using an Incident Light Meter

Balancing Flash and Ambient Light Using an Incident Light Meter

Balancing Exposure

Ambient underexposed by two stops by changing the shutter speed to 1/40th of a second

Why is an incident meter important for flash photography?

How often have you struggled trying to capture a well-exposed portrait in a dimly lit room or hall. All you have is the ambient light and your speedlight. With an understanding of exposure and flash techniques you can learn to successfully balance ambient and flash exposures to create exceptional photographs. Ones that look natural, without the harsh appearance of flash, and without detracting from the ambient light.

For the most part, your camera’s meter and exposure evaluation will be just fine when you are capturing images in even light situations.  However, the onboard system will usually fail when you are trying to properly expose a subject in a dimly lit room.  In these situations, you must be in a position to balance the ambient light that is in the room ,and the light from the flash that will light your subject.  The same concept applies to photographing subjects in low light situations outdoors.

The camera’s metering system is not capable of evaluating the two light sources and establish the correct exposure for the scene, or in other words, balancing flash and ambient light.  The camera’s meter when set to evaluative (Canon) , matrix (Nikon), centre-weighted, or spot metering works great for a balanced scene, but not when the exposure of the environment is vastly different than the exposure of the flash lit subject.

Two examples of how in-camera metering systems fail

Choose a camera capable of using a hot shoe or off-camera flash to follow along.  The pop-up flash is not suitable for this exercise. Keep the aperture value at f/4 and the ISO at 400 for each scenario.

In the first image, below, the flash is set to ETTL (electronic through the lens meter system).  The camera is set on aperture priority and evaluative metering mode.

Notice that the subject is reasonably well lit but the background is under exposed.

Notice that the subject is reasonably well lit but the background is under exposed

For this next example, set the meter to the spot metering mode and take the reading for the background. All other settings remain the same and the flash is still on ETTL. Notice the overall image is now underexposed.  The metering system is unable to properly evaluate the scene and the primary subject. (image below)

flash-photography-lighting-metering-02b

For the third image in the sequence turned off your flash, and set your camera evaluative/matrix metering.  The idea is to try and get the best exposure for the background. Make note of your shutter speed and exposure settings.

Shutter speed 1/13th second and the background is reasonably well exposed, though not perfect

Shutter speed 1/13th second and the background is reasonably well exposed, though not perfect

Using a hand-held incident light meter to solve the problem

Good hand-held meters have multiple modes: a spot metering mode which is a reflective reading (usually 2 degrees or less), an incident mode using the meter’s light dome, and one or more flash modes.  It is imperative you learn the proper use of these modes in order to be successful at flash photography.

You want all your images to be good, not the occasional 1%.  You need to stop struggling and juggling settings to produce the image you want.  Experiments are good only if you know what you are doing and what your tools are.  Realize that there are infinite ways to light your subject with strobes, as there are infinite scenarios that your subject can be in. So learn how to expose correctly, learn how to balance ambient light and flash, but most of all, learn how to read light.

Set up the ambient exposure first

Let’s go back to the scene as we had above.  Set your camera to manual exposure mode. As before, keep your aperture at f/4. Next, to properly expose the room you measure the ambient light using the spot meter function of the hand held meter pointed at an area that is mid tone (approximately the same as medium grey) in the scene.  In this test case the meter indicated 1/10 sec at f/4.  Set your camera to these settings. Take a test shot to ensure your exposure is correct for the ambient light. See below:

Test exposure using ambient light only

Test exposure using ambient light only

Next set the flash exposure for the primary subject

You can experiment with off-camera flash if you do not have remote triggering capability, using an off-camera remote flash cord (for Canon, or Nikon). On-camera hot shoe flash use is not recommended as it produces harsh, flat lighting. But in order to simplify this exercise, you can use the hot shoe flash mounted on you camera.  It will be just slightly off center when you have your camera oriented in portrait mode.

To read the flash exposure, set the hand held meter to “incident” mode, and the exposure on the “flash non-cord” setting (do not use the corded or triggered setting). This will read the light falling on the subject when the flash is fired.  If you are using a remote trigger, then the next step is easy.  If not, then have someone assist you for the next reading.  Position the meter such that the dome points to the camera and fire the flash.  At full power, in this test case, the reading was f/19.  See the image below:

How to point your meter and measure the flash

How to point your meter and measure the flash, this is obviously too much power

An f/19 reading indicates overexposure, as your camera is set at f/4 for the depth of field you want. To resolve this, you need to dial down the output of the flash by five stops (f4 > f5.6 > f8 > f11 > f16 > f19>.  Set the flash to 1/32 power which is five stops below full power. It is always good to take another test reading and adjust the distance of the flash to subject to compensate for a half stop variance (to f/19).  Now you should get a reading of f/4 and you are ready to shoot.

Flash and ambient balanced successfully

Flash and ambient balanced successfully. The exposure on the subject is perfect and the room is properly exposed too.

Adjust shutter speed to feature the subject more

Basically, the settings on camera indicate equal exposure and you can see that both the subject and the room are exposed correctly at an aperture of f/4.  This is good. But, if you want to emphasize the subject more, you want to underexpose the room. With the way you have your exposure already set up, this is really easy. All you need to do is increase the shutter speed by a stop, two stops, or more. This under exposes all the areas lit by the ambient light but the exposure on the subject remains the same and is always correctly exposed.

Ambient underexposed by one stop by changing the shutter speed to

Ambient underexposed by one stop by changing the shutter speed to 1/20th of a second

Ambient underexposed by two stops by changing the shutter speed to 1/40th of a second

Ambient underexposed by two stops by changing the shutter speed to 1/40th of a second

The reason for this is that the meter reading for the background is based on the ambient light. The subject however, is lit using the flash, an instantaneous light source. Your flash exposure is controlled by its power output, increasing or decreasing the flash’s distance from the subject and by the aperture setting on your camera. Typically, flash exposure is not affected by shutter speeds as long as your camera’s shutter speed is set to the flash sync speed or slower. As a result, changing the shutter speed affects the ambient light exposure (the exposure of the room) without affecting the flash exposure (the exposure of the subject).

Summary and action plan

In conclusion, relying on your camera’s metering system, be it evaluative, spot or centre-weighted, never gives you the kind of exposure control that you can achieve when using a good hand-held incident light meter.

If you have additional tips or tricks please share them in the comments below, and if you haven’t tried your flash off the camera yet why not give it a go!? Grab yourself a light meter and try it!

Read more from our Tips & Tutorials category.

Shiv Verma is a photographer, educator and technologist and lives in Wrentham Massachusetts. He is an avid wildlife and commercial photographer and conducts photo workshops and tours worldwide. You can check out more of his work on his website.

  • Eric Bryan

    One of the best articles I’ve seen here in a while. Refreshing to see a topic covered from a new angle that isn’t a rehash of the same old basic stuff over and over and over.

  • Rick

    I think this article makes it sound easy to do ambient + flash indoor portrait. In fact, too easy. They key to balancing ambient + flash, in my experience, is not the two exposures. That part I think is easy once you get a handle on it. The difficult part is avoiding color difference between flash and the ambient. You can gel it to certain degree, but sometimes it doesn’t work if the ambient has funky color cast – e.g., fluorescent. Because of that, I’d rather kill the ambient and rely on flash only for indoor portrait. You have other problems as dark background, but you’d have to work your way around it by bouncing flash, etc.

    It’s odd that the author doesn’t make a single mention of “gel”, which I think is perhaps as important as getting the double exposures correctly.

  • Shiv Verma

    Rick – thanks for your comments. I intentionally left out color balancing and the use of gels so as not to make this an article too large to digest. You are correct about the funky ambient light and that is wen controlling the shutter speed will help either kill the ambient completely or tame it to a point of acceptability. I will consider an additional article bringing in secondary flash heads and tells to correct white balance issues. Thanks again for commenting.

  • Shiv Verma

    Eric – thank you for your comment and kind words. Most appreciated.

  • Rick

    Hi Shiv, thanks for the follow-up. Yes, I’ll look forward to your next article.

  • marius2die4

    A practical article. I enjoy to read. Congratulations and I Wait to read the next one;)

  • Shiv Verma

    Thank you.

  • Edmund

    Hi Shiv, I understand your article completely. A hand-held flash meter is really a rarity in the world of digital although was necessary with film cameras (unless you had a Polaroid back). I cannot see that it is something one would take on location so it is really more for a studio shoot and given this you would have plenty of time to practise before your model / client came into the studio. On location, you need to rely on experience and multiple bracketing and this all depends whether you are shooting with a reflector or a softbox or just bouncing the flash.
    Good article technically, not sure how much help it is to your “average Joe”.

  • anotherview2

    Thanks for this instructive, helpful photo essay on balancing exposure involving flash lighting and ambient lighting. I’ve printed out this essay, and will follow it to learn the balancing technique.

    I note you mention the use of a light meter yet offer no basic instruction in its use for doing this technique. Let me note also I’ve read that the photographer can use the camera’s metering system to function similar to a light meter for reading the two exposures. If you do a later essay on the lighting technique, you could explain more about each metering approach.

    I own a light meter but have yet to learn its use. Besides myself, others may appreciate another photo essay from you explaining the use of a light meter in balancing exposure.

    As to the gel issue for a White Balance between the subject and the ambient color temperature to match their WB appearance, I understand two schools of thought exist here. One says the ambient light WB as it presents itself reproduces the given environment. The other view prefers gelling the flash lighting for matchng the WB of subject and background. Which one a photographer chooses depends, it seems, on the use of the photograph or the photographer’s intention.

    Thanks again for your photo essay. You have a skill for written instruction.

  • Michael in Toronto

    Great article, and completely timely as I was JUST discussing this with a friend who wants to better understand flash and ambient exposure!!

    ….perhaps out of scope for this discussion but a topic for next time is the WHITE balance unmentioned in this post. You’ll note the dining room full of incandescent (yellow) light and your mannequin lit by 5000°K (or thereabout) flash—or white light—-and some would say is therefore NOT correctly exposed. The juxtaposition SCREAMS flash/ambient mix because there is a mix of white balance! The two (foreground AND background) could be neutral/equal/the same by quickly adding a CTO (colour temperature orange) filter on your flash and choosing tungsten on the camera and VOILA! Neutral (no yellow colour cast) background that matches the foreground. It’s easy to do and neglected by 99% of shooters (come to think of it—keep it up! you guys are making me look good—er um at least technically “better!”)

  • Shiv Verma

    Hi Michael,

    Right on – thank you. As i had replied on an earlier comment, i will do a followup article on this subject as well as the use of light meters.
    Best,
    Shiv

  • Shiv Verma

    Hi, Thanks for your comment and feedback. I will follow-up with an article on how to use a light meter for flash as well as non flash photography.
    Thanks again.

  • Shiv Verma

    Thanks Edmund. Appreciate your feedback. I will do a few more on the topic and simplify for as you stated, the “average joe”. Your comments are valuable.
    Best,
    Shiv

  • Darlene Hildebrandt

    Oh I dunno about that Edmund. Maybe I’m still old school as I did shoot film back in the day, but I still use my light meter whenever I use off camera flash. I don’t like guessing, I prefer knowing. I tend to prefer to use non-TTL flash so I have more control over it and get predictable results. So I do take my meter on location.

    As for the “average Joe” if the average Joe wants to be more professional and take better photos than the other average guys, I think it would help him. If he wants to stay “average” then maybe not. ;-) (said tongue in cheek)

  • Darlene Hildebrandt

    Glad you liked it Eric, I thought it was well done also.

  • anotherview2

    This wording goes to the point: “but I still use my light meter whenever I use off camera flash. I don’t like guessing, I prefer knowing.”

    I say so because I have enough experience under my belt to appreciate the necessity of capturing a good exposure in the camera. Lately, I have reached this skill level, but I hunger for more improvement in doing an exposure involving flash lighting. I know the use of a light meter can help here.

    I look forward to the photo essay on this technique.

  • Rahul.G

    Ummm… What if I use Slow Sync flash and set exposure compensation (as required) ???
    Sorry if this is a silly question as I’m complete newbie in this… :P

  • Darlene Hildebrandt

    not sure what you mean? Like set it on Shutter priority instead? Then if the background or ambient light is dim it will open up the aperture wide opened. What do you mean by slow sync?

  • Edmund

    Hi Darlene. I take landscape photos which (almost) never require flash and travel photos where a flash is either illegal or inappropriate or there just isn’t the time to do more than bracket. You are talking about controlled studio situations, I cannot leave my camera on its tripod in the middle of a crowded city while connected by only the remote cable to measure a flash intensity (by which time the subject has moved anyway). Maybe you always have an assistant but your “average Joe” does not. Although My flash is TTL connected by a cable to the hot shoe so it is off camera, normally with a diffuser or bounced from a reflector, and I use a tiny manual flash with a slave as fill-in I can set the camera to bracket a range of flash strengths.
    So the term “location” is clearly different for the professional like you and Shiv. For me it could be a busy street at dusk when the Spanish have spectacular Easter parades where they are all dressed in “Klu Klux Klan” hoods to provide anonymity and each “Klan” has different coloured outfits and the evening light is fading fast so the degree of flash intensity needs to be changed (as very well described in Shiv’s article). I have a very patient assistant in my wife who stops the crowds from tripping over my tripod and from stealing the camera but I simply couldn’t step out into the middle of a parade, take a flash reading and return to set up the photo before the whole thing had moved on.
    I really appreciate that you are moving this website upmarket and I agree wholeheartedly that it was directed at beginners before whereas you are targeting the middle ground which is the “average Joe” (me) and is much more interesting for enthusiast photographers. However, clearly this is not targeted at professional photographers (who are too busy making money elsewhere) so I think there needs to be a bit of the practical side as well as the theory.

  • squeakyweasel

    Think you perhaps mean 1st or 2nd curtain (flash sync) modes Rahul?

    These are more traditionally methods of capturing action and movement with DSLR cameras over longer exposures. They work by triggering the flash to fire; either at the instant of the first shutter (or curtain) opening to capture subsequent movement over the top of the frozen image OR at the instant of the second shutter closing to capture the frozen image over the top of the movement.

    There are articles on this subject right here on DPS if you search. While these methods can admittedly help to liven up an underexposed BG they are
    hit-and-miss unlike the method brilliantly explained in this article that has now added another expensive gadget to my wish-list!

    With that in mind … any recommendations for a “not-too-expensive” good quality light meter like the one discussed folks????

  • JvW

    This article, http://digital-photography-school.com/slow-sync-flash , explains both slow sync and rear and front curtain.
    What Shiv Verma described above is basically slow sync: vary the shutter speed to get more or less ambient light, and vary the flash power to light the subject. In the above case it’s all done manually.

    A camera has a certain maximum speed for flash photography. At shutter speeds faster than that sync speed you get a black or dark beam on one side of the image because the curtain starts to close before the flash is fully expended.

    Any shutter speed slower than the sync speed can be considered slow sync.

    Many simpler cameras set the shutter to the fixed sync speed for flash photography.
    Slightly more advanced types allow you to let the camera choose a speed from slow up to max sync speed. That works in aperture priority, where you set the aperture and the camera decides the shutter speed as usual, but now no faster than sync speed.

    If you use exposure compensation in aperture priority, the camera varies the shutter speed so that ambient light gets compensation, but the flash power remains the same. In this case, to vary flash power, or the light on your subject, you need to use flash exposure compensation. Or of course, you could use manual flash settings to set the power yourself.

  • Barry E Warren

    This is a great lesson, Thanks …..Nothing like a good refresher…..

  • Darlene Hildebrandt

    No you’re right travel is different. I am talking about controlled shoots on location like a portrait. There will be a good mix of different levels of articles on dPS from beginner or “Average Joe” all the way up to advanced and pro. We survey our readers and they cover the full gamut so we want to make sure there is something for everyone. If one article is not for you I’m sure you can find 3 others applicable to what you do. Not every subject or topic will be each person’s cup of tea either, you can just pick and choose which to read that will be helpful for you. I hope that helps.

  • http://www.shivverma.com/ Shiv Verma

    Hi Barry, Glad you got something out of this one. Appreciate your comment. Best, Shiv

  • Darlene Hildebrandt

    Mr. Weasel – I personally use this one Sekonic 308. It’s simple and any less than that and you’re into made in China and not so reliable or long lasting.

  • christo

    Great Article, I was searching such illustrative article for long time. Awesome work Thanks a bunch. I was planning to buy light meter this thanks giving, now I decided to buy it.

  • http://www.shivverma.com/ Shiv Verma

    Hi Christo, Thanks for your feedback. Once you start using a light meter you see how much your exposures will be spot on. Best, Shiv

  • christo

    Hi Shiv, I was planning to by Sekonic L-308S. What you think about this? I heard, it doesn’t have ability to take aperture measurement, It always take the shutter priority mode.

  • http://www.shivverma.com/ Shiv Verma

    Hi Christo, I do not use this one but have heard it is very good but if can spend a little more the 358 is an excellent choice.

  • Darlene Hildebrandt

    Matter of fact I DO have the 308 and it works fine also, had it for years.

  • christo

    Hi Shiv, Thanks for the suggestion, I looked for 308, looks like no one sells that now. :( Do you have any suggestion on any other one ? even other than Sekonic ? Sorry for asking too many questions

  • christo

    Hello Darlene, Thanks for the reply, How do you manage if you need metering for specific aperture on 308?

  • http://www.shivverma.com/ Shiv Verma

    If you are in the US go to my web site and under products click on Adorama and the search for the L-308S – it is available for $233.

  • Darlene Hildebrandt

    same as any other – you set it on flash mode, press the button and it tells you the exposure for the flash. If you get a reading of say f/11 and you want to shoot at f/5.6 your flash needs to get turned down 2 stops. Do that and take another reading.

  • Darlene Hildebrandt
  • http://www.shivverma.com/ Shiv Verma

    The followup article was posted yesterday.
    Best.
    Shiv

  • Just Another Sunday

    Thanks so much. How can I subscribe to your tutorials?

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