balancing flash with available light / ambient exposure
Since many of the questions I get on the Tangents blog relate to balancing flash with available light, I want to pull the replies together into a single article. A reference point again, instead of the replies scattered throughout this website.
The answer to the questions about how to balance flash and ambient light, is often along the lines of “it depends”. It really depends on:
- the scenario you have, and
- what you want to achieve.
Now that all sounds quite vague. Being told that you can pretty much “do what you want”, doesn’t help if you don’t even quite know where to start. Most of the answers are in the linked articles there, and on this page on my Top 20 Flash Photography Tips.
But, let’s look at one specific image, and analyze what our options are, and see if we can make sense of it all …
I had the pleasure challenge recently of photographing this super-cute Jack Russell terrier of clients of mine. Sundae just loves snow! So after one of the heavy snowstorms, we went to a park where I could photograph her acrobatically snatching at bits of snow hurled at her. She was very fast! Even with the Nikon D3 set to maximum burst rate of 9 frames-per-second, I could barely get 2 frames before she was back on the ground.
So there were a few challenges.
- I needed a responsive camera, and a lens that focuses fast. The Nikon D3 and the brand-new Nikon 70-200mm f2.8 AF-S VR II (B&H) took care of that. This lens is surprisingly fast to focus for such a large optic.
- I needed a very fast shutter speed, and enough depth-of-field. A few initial images showed that I was getting movement blur even at 1/2000th of a second. I therefore pushed up my ISO to 800, and settled on 1/8000 @ f5 for the majority of the photo session.
- focusing modes. With the D3 set to AF-C (continuous focus mode), and 51 AF points, I let the camera control most of the focusing for the session. For a few more static images, I did flip to AF-S mode to be sure of exact focus on her eyes.
- I was again surprised by my success rate. To compensate for how difficult it was to get a neatly composed shot of Sundae, I completely over-shot and had to wade through more than a thousand images to pick the best for my clients. Of those, about 250 were solid keepers, so it was tough to pare the selection down further to just give the best and most representative shots.
- exposure metering. The metering was actually the easiest part of the photo session …
This topic – balancing flash and ambient exposure – seems to one that many newer photographers struggle with. The big hurdle seems to be the basic starting point – how do you decide on the exposure for each?
I’d like to explore this topic a bit with this post. The trigger for this was a question that someone emailed me regarding an image in my book on flash photography. Instead of answering the question directly, I thought that a wider answer might be more illuminating. We’re still on that perpetual quest for more aha! moments. So let’s see where we head with this. (I’ll come back to the specific question and answer at the end of this.)
But why do we even want to add flash to a subject when the available light is soft?
The answer is that with flash we can control the direction and quality of light, and create a more dynamic image.
We don’t necessarily just use flash to avoid camera shake and / or poor exposure in low light. We use flash to create better light on our subject. We can ‘clean up’ the light that falls on our subject. Or to create more dynamic and interesting light. It’s about control. We decide. So where do we start?
The simplest approach for me, when I work in fairly flat and even ambient light, is to under-expose the ambient light by a certain amount. Then we add flash for correct exposure. So how much do we under-expose the ambient light by? Well, it depends. Usually a stop is good. Two stops can also work. If you’ve seen some of the images in fashion and music magazines where the subject is in a pool of light .. yet, the sunlit cityscape is darker, then that is because the photographer under-exposed the ambient light by 2-3 stops. Even in bright sunlight. So we have some leeway. That should ease some of the anxiety.
Under-exposing the ambient light by a stop, and then adding flash … is but one scenario, and one recipe. This approach won’t apply to every possible situation you might encounter .. but it’s a good starting point in grasping that Big Question – where do we even start in balancing flash and ambient light?
Let’s start of with an example where the previous method wouldn’t work:
settings: 1/125 @ f3.5 @ 800 ISO
lighting: Q-flash T5D-R, in TTL mode diffused by medium softbox to the right
(A speedlight in the softbox would’ve worked just as well here.)
Here’s the image without flash, just so we have a reference ..
Going by the emails that I receive, one of the areas that many photographers struggle with is that of combining ambient exposure and flash exposure. This question is also expressed in other ways. It can be a frustrated, “where do we even start?” I also often see it expressed as an involved step-by-step deconstruction of technique, making the entire process more complex than it is.
In reply to that, and many other emails I’ve received in the past few months, I’d like to offer an analysis of a few images from a recent shoot.
[ click on the photo for a larger image ]
One of my favourite clients has the most adorable baby boy that she wanted some portraits of. I had to shoot fast, since his attention span was .. oh, zero. He’s still a baby! I also wanted to be able to cover myself in getting some available-light only portraits, and some with bounce flash. I didn’t want the flash to be overwhelmingly bright. And in bouncing the flash, there was also less chance of disturbing the baby. So I had to mix it up in order to get some variety, and be sure of images that worked.
The image at the top was shot with the Nikon D3 and the Nikon 70-200mm f2.8 AF-S
Lighting here was a combination of available light and bounce flash. And as usual, I used the black foamie thing to flag the flash so NO light from the flashgun fell directly on the child.
My camera settings: 1/100 @ f4.5 @ 640 ISO, using TTL flash
The FEC was not recorded, but would’ve been around 0EV because my flash isn’t merely fill-flash here, but fairly dominant.
Now where the settings look like they might be informative, I also often feel that these numerical values are a diversion. Too many photographers will get hooked on the choice of f4.5 over another aperture. Whey 1/100th of a second? Why 640 ISO?
The truth is that this could’ve been a different combination of settings. What is important here, is the quality of light. It is our major concern here, and should interest us more than f4.5 at this moment.
The light on the baby’s face is directional. There is more light coming from camera left .. and from this you should be able to deduce that I did indeed bounce my flash to my left. Using that piece of black foam to flag my flash, I was able to get directional light like that.
The light is soft. Since I bounced my flash into the room, and it bounced off the walls, and furniture, I will have soft light.
So those two aspects of the light from my flash is easily understood – soft directional light.
Now let’s look at how I chose to balance my flash with the available light …
The two truisms regarding flash photography that get thrown around most often, are:
ambient exposure is controlled by shutter speed,
flash exposure is controlled by aperture.
I’ve railed against this before in a post on what I called the urban legends of flash. My take on it is in that in over-simplifying, and bandying around those two statements in a perfunctory manner, we actually lose understanding of how flash exposure and ambient exposure inter-relate.
My problem with the first statement is that it disregards that aperture and ISO both control ambient exposure as well.
It is essential to understand that with TTL flash, things change a little. Actually, things change a lot, since exposure control for manual flash and TTL flash are entirely different.
This specifically is where I feel that the second truism there: “aperture controls flash exposure” is entirely misleading.
With TTL flash, your camera and flash work together to control /calculate flash exposure .. and then adjust the power the flash emits, to give you (what it deems to be) correct exposure … regardless of your choice of aperture, or your choice of ISO, or the distance of your flash to the subject. Of course, these things have to be within reason. You have to work within the capabilities of your flash.
Let’s see how this works. Here are two images that I used in my book on flash photography techniques .. and I’d like to use them with a slightly different take.
With our model, Jackie, positioned in front of a window, we have two things to expose for:
- we have the ambient exposure to consider for the outside background,
- and we have flash exposure to consider for our subject, Jackie.
Ambient exposure for the background – shutter speed, aperture and ISO. Simple enough.
Flash exposure settings to light our subject – well, this will depend on whether we are using manual flash or TTL flash.
As mentioned, if I had used manual flash here (for example with a softbox), then I would have to meter my manual flash for the specific aperture and ISO and distance and power setting of my flash. And then juggle those four things to give me correct exposure as metered with a flashmeter. (Or perhaps checked via histogram.)
But in this case, I used TTL flash that I bounced over my left shoulder into the room.
And I purposely set out to use TTL flash here in a way to illustrate a point:
With TTL flash, aperture effectively becomes transparent. In other words, with TTL flash, our choice of aperture, (within reason), has no effect on flash exposure. (This is also true for our choice of ISO.)
A recent thread on the Flick group on flash photography techniques dealt with exposure metering .. and the questions revolved around understanding your camera’s built in meter. One of the group members, Arnold Gallardo (Zeroneg1), replied with a lucid explanation on exposure metering, relating it to the Zone System in a clear understandable way, using images from my blogs. I’d like to present this article by Arnold Gallardo as the latest guest spot on this blog.
I might not have such a specific linear approach to metering any more during the actual shoot, since with practice it becomes near instinctive .. but this analyzing of a few images might make an interesting outside perspective to the thought-process in exposure metering.
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Zones of Light – an approach to exposure metering using the Zone System
by Arnold Gallardo (Zeroneg1)
We all have made a picture where we didn’t get the representation we wanted it was either too dark or too light or not quite there in terms of how we wanted the camera to capture the scene or how it imparts an emotional element to the image. Then we realize how professionals do it ‘so easily’ when thinking about well exposed and composed images. Well, a Pro would have developed an innate sense of tonal placement and tonal awareness that has been developed through experience as well as ‘seeing’ and not just looking and solving things on the fly.
With the recent posts on lighting the formal wedding photos, a question came about what the flash exposure compensation (FEC) was that I had used. (The image above is from the sequence.) Instead of replying in that thread where the reply might get lost, I thought I’d post it as a separate short article.
My settings for that photograph: 1/100th @ f3.2 @ 800 ISO
and flash was bounced TTL flash.
How much FEC did I dial in? I could answer that my FEC was +0.7 EV, but that numerical value might not contain enough real information …
One of the most popular pages on this site is the one dealing with that often confusing phrase – dragging the shutter. The original page was written a few years back and needed some drastic updating. Not only did I want to improve the text, but the original article also featured some less than spectacular photographs (to be kind about it).
The main text on that page has now been complete rewritten, and I’d like to direct everyone to it and catch up with a more fresh explanation of dragging the shutter.
Based around a new sequence of images, it should be more clear now how a change in shutter speed affects the ambient light only, and not the flash exposure.
For example with this comparison, the settings for aperture and ISO remained the same (f5.6 @ 400ISO), leaving the manual flash exposure the same .. but I changed the shutter speed from 1/250th to 1/60th .. and thereby bringing a huge change in how the background appears.
Since shutter speed (largely) has no effect on flash exposure, it becomes our immediate choice in controlling our ambient exposure when using manual flash. With TTL flash though, it’s a different story … and the details are explained on the new page.
Another question that came in regarding material covered in the book on flash photography techniques ..
Sven Pohle asked:
I am reading through your book (second time already) and have a question about metering plus adding the flash. I do meter for a white tone in my image and add +1.7 or 2 (I’m on Nikon) to my exposure. Now without flash my image is exposed correctly. But if I add the flash then the white starts to blow out as it does add flash light to it. So this is there i am confused. Would you rather go and meter for the background to get that right and then just add the flash to bring the subject up ?
I’d like to answer this here, since I am sure this is a widespread question or point of confusion …
First, to anyone who is confused by the question – part of the metering techniques explained in the book, revolves around using your camera’s built-in meter. We use it to calculate ambient exposure by metering off the brightest relevant tone of your subject if they are wearing white. And in order to do so, we have to adjust our metering so that it places white correctly on the histogram. In other words, we have to correct for our camera’s tendency to expose for everything as a medium toned grey, by pushing up our exposure by around +1.7 stops.
Back to the question about adding flash to available light ..
Let’s break this up into two broad scenarios:
1. Your subject is shaded and your background is brighter.
In this instance, you would expose for your background. You might expose correctly, or you might allow your background to blow out a bit, or even under-expose for a punchier image. Your choice. You would then expose correctly for your subject, using flash, whether TTL or manual flash.
So in that case, you wouldn’t meter off the subject per se. You might meter off your subject to see how much darker he / she is than your background, but you wouldn’t meter specifically for the ambient light falling on the subject to get your camera settings. Therefore you wouldn’t meter off any white tone the subject might have, such as a white shirt or dress, to determine your base exposure. Instead, you’d look at your background.
Here’s an example from a portrait session with a couple yesterday:
She wanted a few photographs with the pathway leading to the beach, but the light was very uneven with the sun pouring through the trees. I therefore positioned her in the shade, and used flash (Q-flash in a softbox) to light her to the same level as the background. So in this case, my background determined my settings.
1/250th @ f11 @ 200 ISO
manual exposure mode on my camera, with manual flash in this case.
(I purposely left the softbox shape in the image here instead of editing it out, to give an idea of the positioning of the softbox.)
How did I figure out my exposure settings here? By using the Sunny 16 rule as a mental starting point, but keeping in mind the sun was getting lower, and then doing a quick test shot and looking at the back of my LCD. I then used the histogram method to get my manual flash exposure settings – which are controlled at this point by the distance between my flash and my subject, and the power setting on the flash. In the end, I had to pull down the exposure in RAW by 1/3rd stop. A minor tweak.
The next scenario is where it gets interesting:
2. Your subject is well lit, but you want to use flash to bring up some shadow detail.
This is where you’d meter correctly for your subject, with little regard for your background. (Unless you have additional lights for the background. But we’re just looking at a simpler scenario where we have one flash and want to light our subject.)
Now, if our subject is already well-lit and properly exposed for, then adding the same amount of light from our flash – ie, “proper” exposure from our flash as if there was little available light – will mean we are adding double the amount of light necessary for proper exposure.
Therefore using getting correct ambient exposure for the subject is the base exposure, and then we’d just add fill-flash .. usually a stop or more under the ambient light. So, using the histogram method or selective metering with the camera’s meter to get correct ambient exposure for the subject works, but we can’t just add equal amounts of flash .. instead, we have to decide how much fill-flash to add.
Here is the couple on the beach in direct sunlight. I got to correct exposure for my ambient light here with a combination of checking my histogram on her white dress, and confirming it with the blinking highlights display NOT blinking for her dress.
Then all that was needed to bring up exposure on the shadow sides a bit, was to add fill-flash. In this case, the flash was once again via the Q-flash and softbox held off to the left of the camera. There is no over-exposure though, since the flash exposure is lower than the ambient exposure.
And as an aside … here is an image where the ambient exposure was purely based on the mood I wanted.
I didn’t expose for my subject per se. However, I did make sure that in my composition they were positioned such that they do stand out from the background. My exposure was based on the overall scene, and not a specific tone. I didn’t want the bright sun in the viewfinder to affect my exposure, so I once again kept to manual exposure mode, and used my LCD preview to get an idea of whether my settings were good.
1/1000th @ 6/3 @ 200 ISO .. and a bit of juggling of values, and you’ll see that I was once again close to Sunny 16 settings. It’s usually a good starting point when working in bright light.
Valerie is the striking model I used for my flash photography workshop held in Nashville the past week. As I mentioned in that post, I will explain a bit more about how I meter for manual flash when using the softbox outside. And just to bring everyone up to speed, here is the set-up as I use it - a speedlight set to manual, pointed into a softbox, and triggered with a PocketWizard.
The lighting is simple – the softbox is held to the my left-hand side in this instance. The colours and contrast is something I adjusted in ACR (hosted in Bridge), as part of my usual post-processing workflow. And here is the available light image before flash was added.
As you can see in this image, I let the available light under-expose by a stop. I metered for the available light with a hand-held meter here, but I could just as well have used the histogram method .. and then I take my exposure down by 1 stop. I could do this via my shutter speed or aperture or ISO choice .. or a combination of those.
The lightmeter that I use is the Sekonic L-358 (B&H). I have it with the built-in module that triggers the PocketWizards as soon as you press the metering button on the flashmeter. It makes it much less clumsy to use. But using the histogram and selective metering off her white shirt gets you there as well with as much speed.
My settings for the sequence of images here were: 1/200th @ f5.6 @ 200 ISO.
The ambient light was metered at 1/200th @ f4 @ 200 ISO. Once again, this could’ve been done with either the flashmeter here, or by using the histogram.
I then changed my settings so that I would underexpose the ambient light by a stop. I could’ve changed any of those settings, or a combination of them. In this case I simply dialled down my aperture to f5.6 since I was already at the minimum ISO for this specific camera. Then I set my speedlight to a specific power setting …
Manual flash is determined by 4 factors: – aperture
- ISO
- distance from the light source to subject
- and flash power setting.
In this instance, we have determined what aperture and ISO we would like to be at … which just leaves distance and power of our speedlight to be determined.
So how far do we hold the softbox from the model?
This is where we balance out the decision based on a couple of factors. The larger the light source (in relation to our subject), the softer the light .. but we also need a comfortable working distance so that the softbox doesn’t appear in the image. If we hold our softbox too far away, then the light progressively becomes harder. Therefore, in practice, we would slow ourselves down if we worked precisely according to textbook formulas and set-ups. It is just easier to be flexible about it on a shoot, and find that sweet spot where the light still wraps around your subject to an extent .. and you have enough space to move around without having to change the light’s positioning too often.
Here, as part of the workshop demonstration, someone was holding the softbox up for me on a monopod. This makes it much easier to change the position of the light as the model moves around.
When we’ve figured out the approximate positioning of the speedlight and softbox, then we need to adjust the power to where we get f5.6 – but there is some flex built into doing it this way. If we need a 1/3rd stop more or less light from our speedlight and softbox, we can just move the softbox closer or further away by a slight amount. This is an easier way to adjust the manual flash that continually hoisting it up and down to adjust the power ratio on the back of the speedlight.
And then of course there is also the leeway built into using the RAW file format. In the image at the top, I had to pull down the exposure slider in ACR by 2/3 rds of a stop. It seems that somewhere during the shoot the person holding the light up, might have moved a little closer. But this is less of a concern while taking the photo, than keeping the rhythm of the photo sesssion. Rather than a stop-start way of adjusting the lighting, it is better to take up that slack in exposure precision, while editing the image.
So while it might seem that there are a confusing number of settings we need to adjust, they aren’t entirely random and they do fall into place with a certain amount of logic.
And to re-affirm everything, here is a previous post which also covers this topic - so, what are your settings?
