What's the best way to make up for lost exposure when reducing flash power?

I've set my camera up to use Auto ISO, with a minimum of 1/60th second shutter speed (to stop camera shake), and mostly using direct built in flash on my Nikon D3100 for family photos. I think I’m probably a beginner to intermediate level amateur photographer but would love to learn more.

I'm finding that I don't like quite as much flash light on my subject (usually my child) as what my camera tends to give out. So, I've been reducing the flash compensation to address the issue. However, the camera doesn't try and automatically make up for lost light exposure by other means and the photos taken are dimmer than what they should have been if the available light isn’t enough for a full exposure. So, I'm interested how other photographers would make up for the lost exposure. The 2 ones I can think of are increasing ISO manually or using a slower shutter speed (or both). Maybe even standing further back when using the flash instead of using flash compensation.

I'd really like to hear other people’s opinions on the matter.

Thanks.

P.s I also have a SB-400 external flash that I use as bounce flash sometimes, but I don't always find it easy to get the angles right or like that bounced flash look from above, or it's not always practical to use it or carry it around.

First and foremost, pay attention to what the camera is doing. It will tell you when it's underexposing.

Second, chimp the images on the camera's monitor, and learn to read a histogram.

And when all else fails, shoot in raw so you can pull out shadow detail much easier in post.

Try turning off auto ISO.

Horoscope Fish said:

Try turning off auto ISO.

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So, reduce flash compensation and adjust the ISO up manually?

I thought about that, but doesn't increasing the ISO make the camera more sensitive to all light, including flash light?

paul_b said:

So, reduce flash compensation and adjust the ISO up manually?

I thought about that, but doesn't increasing the ISO make the camera more sensitive to all light, including flash light?

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It does, but it doesn't change the balance between flash and ambient. Wasn't your original question about how to increase brightness in your images after toning the flash down? You can either open the aperture or increase ISO, both of which have effect on both the ambient and flash, and in equal amount. On the other hand shutter speed only affects ambient.

If the flash still seems too powerful after you have increased ISO or opened aperture, dial it down some more.

pforsell said:

It does, but it doesn't change the balance between flash and ambient. Wasn't your original question about how to increase brightness in your images after toning the flash down? You can either open the aperture or increase ISO, both of which have effect on both the ambient and flash, and in equal amount. On the other hand shutter speed only affects ambient.

If the flash still seems too powerful after you have increased ISO or opened aperture, dial it down some more.

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Pforsell. I think your advice is exactly what I was looking for. Thanks

I'm curious. If auto ISO is on, why doesn't the camera increase the ISO in response to the flash EV being dialled down, thus automatically correcting the needed light exposure?

I'm suggesting you turn off Auto-ISO and simply choose an appropriate ISO for your needs. In my experience Auto-ISO does not play well with flash so I never combine the two.

Indoors I find ISO 400 used with f/4, or thereabouts, is a good start; assuming there's some ambient lighting to work with of course. As for flash compensation, I suggest you try setting it to (-1.5) EV... Once you turn off Auto-ISO, of course.
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I only use Auto ISO for varying light conditions when I don't want to constantly be fiddling with ISO adjustments (as the sun peaks between the clouds on a partially sunny day, for example). And, like Fish, I've found that it doesn't play well with flash. There are plenty of youtube videos on how to shoot with flash, probably some with your camera. Good luck.

paul_b said:

I'm curious. If auto ISO is on, why doesn't the camera increase the ISO in response to the flash EV being dialled down, thus automatically correcting the needed light exposure?

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It unfortunately seems that auto ISO, auto flash (i-TTL) and auto metering (matrix) together build a maze that the camera brains cannot reliably find a way out. And if you decide to add auto exposure mode (P, A, S, scene modes) to the mix, there's too many moving parts to get consistent results.

The gadgets need human intervention. Luck has nothing to do with it and auto modes are brainless random modes. Our brains can solve these problems because we understand what is important in the scene and what is irrelevant. Lighting a model pleasantly and beautifully is art, and operating the gadgets to get what we want is skill. Some of us are born with art in their veins, but the skill part needs practice, a lot of it.

I have solved this equation by using fixed ISO, manual exposure mode, shutter and aperture adjusted for the ambient, and often i-TTL with manually fine tuning the flash output. In my typical usage scenarios I have found that
* bounce flash usually needs +1 stop flash compensation
* direct flash in i-TTL BL mode none and
* i-TTL direct about -1.7 stops FC

Whenever the scene is static enough to allow it, I prefer to use manual flash too. If I mess up, there's no one else to blame. I don't recommend my style to anyone, it just is the way I have done it 30+ years.

Also note, that the Nikon exposure meter weighs the active focus point. In auto modes the exposure/flash output depends on where the AF point happens to land. In the same scene if it is on the brides cheek, on her white dress or on his black tux, the exposure settings will differ. Not as much as when using spot metering, but a little bit anyway.

Find an agreeable model or a skin-toned mannequin head, make a pot of your favorite hot beverage, and shoot one set of flash batteries flat. Make notes as you go. Try to find simple to remember rules-of-thumb (like mine above) to use as the base point. Fine tune in location as needed (colored ceiling, high ceiling, windows, ...). It is not rocket science and you can adjust small image brightness and white balance issues in post processing in a few seconds.

Lots of great advice. Thanks

So reducing flash ev and manually controlling ISO is the way to go.

What about what mode to use whilst doing that. Could you still use P mode, or would you venture into shutter speed or aperture mode for best results or control?

paul_b said:

So reducing flash ev and manually controlling ISO is the way to go.

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I would say so, yes.

I never use Auto ISO when shooting with flash and typically back off the flash EV by one or one-and-a-half stops. Try it yourself and see if it works for you.

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paul_b said:

What about what mode to use whilst doing that. Could you still use P mode, or would you venture into shutter speed or aperture mode for best results or control?

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As a rule of thumb I'd use Matrix metering, Aperture Priority with an aperture of f/4 and ISO 200 for shooting indoors. These settings assume there is at least enough ambient light that I could read a magazine comfortably. If I'm concerned about depth of field then I'd adjust the aperture, either up or down, as I felt I needed to in order to get what I want.

You might also want to consider a hot-shoe mounted flash so you would have the option to bounce the light off the ceiling or wall. This prevents harsh shadows and that washed out "flash look" you can get when using direct flash. A good suggestion would be the Yongnuo 568EX II which would set you back about $100. Lots of power and a lot of flexibility as compared to the built-in pop-up flash you're using now.
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paul_b said:

I'm curious. If auto ISO is on, why doesn't the camera increase the ISO in response to the flash EV being dialled down, thus automatically correcting the needed light exposure?

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There is a little more to it. I don't know your camera mode, so I will assume Auto, or A mode, or P mode.

In those modes. there is a Minimum Shutter Speed With Flash, most likely 1/60 second (some other camera models have a menu E2 to select it).

Do this very simple experiment, so you can see it happen, and will understand what is happening.

So in an indoor scene, with the flash turned off (internal flash door shut, which may not be possible if in Auto mode, maybe use camera A mode to see this),

then aim the camera at a similar indoor scene. Assuming Auto ISO, perhaps it is like ISO 3200, f/5.6, and 1/30 second shutter speed (this can obviously vary, you could tell us the numbers you see). My explanation depends on it being less than 1/60 second shutter speed, very often true indoors. P mode and very high ISO will be a wide open aperture, and might be a faster exception?

Then reach up and turn the flash on (open the internal flash door). The shutter speed will jump up to this Minimum shutter speed With Flash of 1/60 second, but the ISO 3200 and f/5.6 that it set will not change. It is not about exposure, 1/60 is faster than it was, which will underexpose the ambient. The idea is that you are now using flash, and don't need a very slow shutter speed (in camera A, P, or Auto modes).

This is an underexposure of the ambient light... 1/60 is too fast for the ambient. But no matter, because we are now using flash. However, you say you then are using Flash Compensation to reduce the flash output.

If the ambient exposure were sufficient, this may not matter, if the ambient exposure were acceptable. But since you need flash, probably it is not.

When the ambient exposure is near acceptable (very high ISO), the flash becomes just fill flash, and the ambient is considered the main light. But the 1/60 second (flash minimum) is limiting it, it will underexpose.

Indoors with flash, it is common to not use Auto ISO. For the reason just mentioned, and also because the incandescent ambient light is probably orange, making proper white balance be very difficult. In any formal portrait situation (with stronger flash), the goal will always be minimum ISO and a high aperture (like f/8) and the fastest possible sync shutter speed (1/200 second), to intentionally shut out all orange ambient, to keep white balance easy.

Indoors, it is more common to use much less ISO with flash (maybe ISO 400 as actually needed for the little internal flash, but not ISO 3200), which makes the ambient be very underexposed, including at the additional 1/60 second flash will impose. Maybe shutter speed was 1/4 second with the flash turned off, and so 1/60 with flash is less. But the flash takes care of it. And is not likely too much light if the ambient is insignificant.


But now we have to learn about flash. Note that flash exposure depends on distance. Flash maybe be correct exposure at the subject distance, but will overexpose closer things and underexpose farther things (inverse square law). So the first thing to learn to deal with is the inverse square law falloff.