One thing I still don't get with fill flash

[Vertigo1]

Taken delivery of my shiny new 430EX II today and going to start playing. Have been reading all the various guides but there's still one thing that's bugging me.

When using "fill flash" mode, i.e. Av, Tv or P with high ambient light levels, the guides all state that the camera "meters for ambient light conditions" and then fills in the foreground using flash.

My question is, if the camera is metering for ambient light, then surely the exposure will be what it should have been without a flash at all, so when the flash goes off surely it would then over-expose the image?

Got a feeling the answer is obviousl but can't wrap my brain around it - can anyone shed some light for me (see what I did there?)

 

[kennysarmy]

it could be over-exposed but you would just adjust FEC to suit....

 

[philthejuggler]

I use fill flash in almost all my outdoor photographs of people. I find that setting the flash to HSS with no FEC gives faces with an obvious 'I've used flash' sort of look. If the background is dark then the faces can go over exposed.

For most purposes I find -2/3 stop FEC dialled in on the flash is perfect.

Phil

 

[Vertigo1]

So the flash is literally just lifting shadows in faces a little?

What ambient metering mode is generally used? I'm presuming the standard evaluative as presumably centre-weighted or spot would meter more accurately for the subject's face, irrespective of surroundings/backgroud and thus any additional flash would be unnecessary/unwelcome?

 

[SealBeard]

For most purposes I find -2/3 stop FEC dialled in on the flash is perfect.

Phil

What phil said.

the camera is metering for the ambient, and the background also. If the camera is metering for a backlit subject, the camera will under expose your subject most likely. The fill flash will help to light your subject so that it is on par with the BG...

not the best explanation but its late

 

[SealBeard]

So the flash is literally just lifting shadows in faces a little?

What ambient metering mode is generally used? I'm presuming the standard evaluative as presumably centre-weighted or spot would meter more accurately for the subject's face, irrespective of surroundings/backgroud and thus any additional flash would be unnecessary/unwelcome?

If your camera meters for your subject - its possible if your BG is light, it could blow highlights, for example you may blow the sky white.

 

[HoppyUK]

E-TTL flash exposure measurement is done by firing a pre-flash just before the shutter opens. It measures this and then moderates the main flash to give correct exposure. Of course, the camera already knows what the ambient light exposure should be, so it can balance the two.

The pre-flash happens so quickly you can't normally distingush it from the main flash, but if you use Flash Exposure Lock (FEL * button) or use second curtain sync, the two flashes are visibly separated.

Some folks don't realise there is a pre-flash happening at all but all modern auto-TTL systems work this way.

The only thing that commonly fools E-TTL is off-centre subjects, in which case use FEL (see handbook). Works a treat.

If the flash exposure is too light or dark, use the +/- compensation on the gun to moderate the flash power a little. If the ambient exposure is a little off, use +/- compensation on the camera. Most people use Av for fill flash, and if the ambient light is very bright just switch the flash to HSS and it will automatically enable this function when a shutter speed over the max x-sync is needed. Sorted

 

[kennysarmy]

Most people use Av for fill flash, and if the ambient light is very bright just switch the flash to HSS and it will automatically enable this function when a shutter speed over the max x-sync is needed. Sorted

however not every flash has HSS and it reduces the "power" of your flash..by that I mean it your subject will need to be closer than what you would need it to be when using flash without HSS for the same lighting effect...

do people really mostly use Av mode when wanting to fill flash??

 

[Steve Smith]

do people really mostly use Av mode when wanting to fill flash??

I think the only way to fully learn what your flash is doing is to do it all manually and change just one setting at a time to see what changes.

On the rare occasions I use fill flash, I do it manually because I don't have any other options. It's not really that difficult to master.

I'm not suggesting that you should use manual instead of the auto modes - just try it in manual as a learning excersise.


Steve.

 

[Vertigo1]

Thanks guys, you've confirmed most of what I already discovered by reading the monster EOS Flash article

It's just the ambient metering when using fill flash that has slightly confused me. Let's take a couple of examples.

First, say I'm taking a portrait with a fair bright background using evaluative metering. The camera would then meter for the whole scene and, due to the bright background, I'd end up with a slightly underexposed face. In this case I can easily see how the fill flash would help lift the subject's exposure.

Now assume I'm taking a portrait where the background isn't noticably brighter than the subject, say against a wall or something. In this case the ambient metering would likely be accurate for the whole scene, including the face, thus rendering the fill flash unnecessary. Surely firing the flash at all in such conditions would result in slight over-exposure of the subject as the ambient light was already sufficient?

Not sure whether I'm explaining myself clearly here, I probably just need to get out and experiment

 

[Bruce120]

i think getting out there and doing it will be best...I tried to learn in "M" and get my background exposure right then took a shot with flash off, then introduced flash and FEC

 

[HoppyUK]

however not every flash has HSS and it reduces the "power" of your flash..by that I mean it your subject will need to be closer than what you would need it to be when using flash without HSS for the same lighting effect...

Well, the OP's 430EX has High Speed Sync, and you don't need to be closer to use HSS (at least not in the way that you seem to have explained it). You need more power for HSS due to the way it works, but that doesn't mean you have to shoot closer; it means that the flash just has to use more power for a given distance and f/number and ISO setting (both of which you can change to substantially increase range). This in turn means that ultimate distance is reduced but there should still be plenty of range for fill-flash portraits

do people really mostly use Av mode when wanting to fill flash??

Yes, I think most people do use Av. F/number is the primary control for flash, and on Av you obviously control that, while the camera looks after the background exposure by adjusting the shutter speed.

It's only a convenience/method of working though - use whichever mode suits you. The flash will match whatever f/number is set, either by you in Av or manual, or by the camera in Tv or P.

Thanks guys, you've confirmed most of what I already discovered by reading the monster EOS Flash article

It's just the ambient metering when using fill flash that has slightly confused me. Let's take a couple of examples.

First, say I'm taking a portrait with a fair bright background using evaluative metering. The camera would then meter for the whole scene and, due to the bright background, I'd end up with a slightly underexposed face. In this case I can easily see how the fill flash would help lift the subject's exposure.

Now assume I'm taking a portrait where the background isn't noticably brighter than the subject, say against a wall or something. In this case the ambient metering would likely be accurate for the whole scene, including the face, thus rendering the fill flash unnecessary. Surely firing the flash at all in such conditions would result in slight over-exposure of the subject as the ambient light was already sufficient?

Not sure whether I'm explaining myself clearly here, I probably just need to get out and experiment

You logic is correct, and in a situation like that flash obviously isn't essential. But if you try it, you might like the result with just a dash of fill-flash. As a general rule, I use it most of the time. On dull days, it lightens shadows under eyes and chin and puts a sparkling highlight in the eyes. And you can get exactly the same problems but even worse in bright noon day sun. Wedding photographers often use fill-flash all the time, especially if hats are invloved.

The trick is not to overdo it. If non-photogaphers comment on it, it's too strong. It should be virtually invisible to the uninitiated - they should just compliment you on a nice, bright, lively portrait. As I mentioned earlier, use the +/- compensation controls on both the flash and the camera to moderate the flash/ambient balance.

 

[Eddie1]

with digital just look at the image and press the + or - on the flash power rating its that simple

 

[tdodd]

do people really mostly use Av mode when wanting to fill flash??

I don't know what most people do, most of the time, but I mostly use manual exposure for ambient light, especially when using flash.

Autoexposure is like wrestling with an untamed beast - change your composition a little, or change your subject, and the exposure alters. Why would it do that? I know why, but why would anyone want to use a system that kept changing things just because, for example, you included a little bit less or a little bit more sky in the scene? Stick a bride in a white dress in front of the camera and you get one autoexposure setting. Replace her with the groom in a black suit and the exposure changes. Bring them both into the scene and you get a third exposure variant. Zoom out a little and you get something different yet again. How crazy is that? Did the lighting on your subjects change at any time? No. Should the ambient exposure be changing all over the place? No. Yet with autoexposure it does. :shake:

Now, add a flash into the mix and you have the same problem all over again, with the flash also having a mind of its own. Now, the flash I can live with, but I do not want to have to tackle the foibles of wildly varying ambient autoexposure and flash autoexposure at the same time. I prefer to use manual exposure to "lock" the lighting for the ambient/background scene and then I only have to worry about adjusting FEC for the flash.

For more on flash usage try reading this - http://www.planetneil.com/tangents/flash-photography-techniques/

 

[HoppyUK]

I don't know what most people do, most of the time, but I mostly use manual exposure for ambient light, especially when using flash.
Autoexposure is like wrestling with an untamed beast - change your composition a little, or change your subject, and the exposure alters. Why would it do that? I know why, but why would anyone want to use a system that kept changing things just because, for example, you included a little bit less or a little bit more sky in the scene? Stick a bride in a white dress in front of the camera and you get one autoexposure setting. Replace her with the groom in a black suit and the exposure changes. Bring them both into the scene and you get a third exposure variant. Zoom out a little and you get something different yet again. How crazy is that? Did the lighting on your subjects change at any time? No. Should the ambient exposure be changing all over the place? No. Yet with autoexposure it does. :shake:

Now, add a flash into the mix and you have the same problem all over again, with the flash also having a mind of its own. Now, the flash I can live with, but I do not want to have to tackle the foibles of wildly varying ambient autoexposure and flash autoexposure at the same time. I prefer to use manual exposure to "lock" the lighting for the ambient/background scene and then I only have to worry about adjusting FEC for the flash.

For more on flash usage try reading this - http://www.planetneil.com/tangents/flash-photography-techniques/

That's fair comment Tim. But that is an argument in favour of manual exposure control in general rather than fill-flash in particular. I would say two things (and I know you know this, just making the point ).

Evaluative/matrix metering is quite clever and it resists relatively minor changes in mid-tone scene brightness. It knows what the dynamic range of the picture is by measuring the extremes of bright highlights and darker shadow areas.

As part of its programming if things change within those extremes, it won't shift the overall exposure that much - which is what you want. Not the same as manual of course, and so not quite optimum obviously, but probably not that far out. And with no input from the user. This is significantly different to using centre-weighted or average scene metering, which does not take dynamic range into account and will be thrown by this situation.

However, if the overall scene brightness changes, ie a cloud comes over, evaluative/matrix will see that as a completely different situation and make appropriate changes, as you would want.

I would say that the bride/groom situation is quite unusual and generally there is not that extreme change of bright/dark within the frame. More likely is that the overall scene brightness will change in a social situation where people are inside in bright sun, in shade, a cloud comes over, or they move inside etc. In this kind changing scenario, using manual is a fiddly business and I would rather concentrate on getting the shot, providing the exposure is reasonably close (which it would be) and then tweak it using the compensation controls as necessary. For me, that would be the priority and so the preferred method of working.

However, going back to the bride and groom type situation, or any other scene where you are taking a number of shots where the exposure should not change but potentially could, and you have time to set things up, manual is the way to go

 

[Vertigo1]

Thanks for the all the info guys, and that very useful link tdodd

Regards flash exposure compensation, my 40D only allows for 2 stops either way but the flash says it allows for 3. Presumably this just means that if I want the full 3 stops I have to dial it in on the gun rather than the body? From what I can tell any compensation I dial in on the gun will override anything set on the body.

 

[cyclone]

Regards flash exposure compensation, my 40D only allows for 2 stops either way but the flash says it allows for 3. Presumably this just means that if I want the full 3 stops I have to dial it in on the gun rather than the body? From what I can tell any compensation I dial in on the gun will override anything set on the body.

I'm not sure how Canon works, but on Nikon it adds up, so if you go +1 on the body and +2 on the flash you end up at +3. +1 on the body and -1 on the flash puts you back to square one, which seems a bit silly really.

Regarding your fill flash adding to the background exposure, the inverse square law sorts that out. It's much easier to get your head round the inverse square law, then it becomes pretty easy to see why fill flash rarely affects your background exposure.

In your example of a portrait against a wall, you're not really using fill flash but providing the main light source, in which case you will also be lighting the wall as well as your subject.

 

[Vertigo1]

Just checked the manual and, in Canon's case, the gun does override the body

 

[HoppyUK]

Just checked the manual and, in Canon's case, the gun does override the body

Yes, that's how Canon works.

On the compensation thing, I can't imagine that you would ever want more than +/- 2 stops but if so then switch to manual and you can have as much as you want

 

[Cheng]

What is the rationale behind fill flash? How does it 'selectively' lift shadows...so to speak? I've been thinking about it, and the only theory I can think of is that you are giving a small amount of light off, which compared to the shadow areas, is a lot of light, but not for the perfectly exposed areas...so the shadows get for example twice as much light coming their way, yet the rest of the face is only getting say 1/10 more exposure, which means the bits at correct exposure aren't overexposed. Or is it something else?

 

[philthejuggler]

What is the rationale behind fill flash? How does it 'selectively' lift shadows...so to speak? I've been thinking about it, and the only theory I can think of is that you are giving a small amount of light off, which compared to the shadow areas, is a lot of light, but not for the perfectly exposed areas...so the shadows get for example twice as much light coming their way, yet the rest of the face is only getting say 1/10 more exposure, which means the bits at correct exposure aren't overexposed. Or is it something else?

That's a fair point - I'm not now sure I understand why exactly it works (but I know from practice it does!). I suspect, that is why you get a rather nasty 'I've taken this with a flashgun' look if you don't set flash compensation to -2/3 a stop or so. Chimping seems to be useful for judging the compensation. The darker the background & the small the subject is in the frame the greater the danger of 'obvious flash' seems to be and therefore the greater - FEC required.

I'm guessing but :- with -2/3 a stop you are adding a proportionally insignificant amount to the correct exposed majority of the face, but adding enough light to lift the shadows.

Phil

 

[HoppyUK]

What is the rationale behind fill flash? How does it 'selectively' lift shadows...so to speak? I've been thinking about it, and the only theory I can think of is that you are giving a small amount of light off, which compared to the shadow areas, is a lot of light, but not for the perfectly exposed areas...so the shadows get for example twice as much light coming their way, yet the rest of the face is only getting say 1/10 more exposure, which means the bits at correct exposure aren't overexposed. Or is it something else?

That's exactly how it works

That's a fair point - I'm not now sure I understand why exactly it works (but I know from practice it does!). I suspect, that is why you get a rather nasty 'I've taken this with a flashgun' look if you don't set flash compensation to -2/3 a stop or so. Chimping seems to be useful for judging the compensation. The darker the background & the small the subject is in the frame the greater the danger of 'obvious flash' seems to be and therefore the greater - FEC required.

I'm guessing but :- with -2/3 a stop you are adding a proportionally insignificant amount to the correct exposed majority of the face, but adding enough light to lift the shadows.

Phil

You shouldn't always need to use exposure compensation as a rule for fill-flash, if the background and foreground are correctly balanced.

But it is often necessary, I think mostly when the ambient light level is low and it's rather less fill-flash and rather more just flash with a fairly dark background. If the subject is off-centre that sometimes causes problems which fool the system, so use Flash Exposure Lock for that (see handbook).

Another way of handling it might be to lighten the background by increasing the shutter speed, rather than reducing the flash. Either way, chimping it is the way to go and then adjust flash power and/or shutter speed accordingly Adjusting flash power changes the foreground exposure, adjusting the shutter speed changes the background.

 

[Lensflare]

Vertigo - in your baclit portrait example - wih the washed out background that you mention.

It all depends on what you want to happen. You SOUND as though you are taking what the camera gives you as the result.

In fact, you should be dictating to the camera the result YOU WANT. Do you want the background washed out? If so, over expose it and have the face exposed for a pleasing result. If you don't want the background washed out, then expose it correctly. Then flash the face to the result you want.

YOU have the answer. The camera can do one of two things:
1. It can do as it thinks and you just let it. In which case you get the result the little men in Japan give you from what they try to think you want.

2. It can produce the result you want it to, because it does as YOU TELL IT.

In your backlit portrait example, you have two subjects. The background. The portrait/face. You can light either as you see fit by adjusting the ambient (the light that is bouncing around from the sky, or room lights) and the supplementary lighting (your flash).

If you were taking a picture of a rally car jumping over a bridge you would CHOOSE a lens to produce the result you wanted: a long lens to isolate the subject tight. A short lens to give a sense of the scenery around as well. You would CHOOSE an aperture to give you the effect you wanted - wide aperture (f2.8) to give critical focus and blur the background away. A closed aperture to give huge depth of field and make lots of the scene focussed.

These choices are yours. The camera doesn't make them - it doesn't put its own lenses on. Well, using your flash is no different, but instead of selecting the focal length of the lens, you are CHOOSING the amount of flash light it punches out. You can do this in a variety of ways:

1 on manual you choose the power output, from probably 1/128th of full power in fractions working up to full power. Like apertures and shutter speeds these powers also go in increments of 1/3 or 1/2 or 1 f stop. So next power up from 1/128 is 1/64 (twice as much power - or in reality......a bit more than you had when you used 1/128). Next choice is 1/32, again a bit more light getting punched in than 1/64th.....all the way up to blow the lot in one go. Kerbang, and enough light to sear the eyeballs of anyone in line of sight.

2. On TTL - it gives you a "suitable" amount of light according to the scene read through the lens and for the other parameters you have set on the camera according to a set of rules plugged in by the little men in Japan. The result will be somewhere near and good enough fo rmost purposes. That is why most people use it.

Now, even on TTL you can over ride the system and make it do what you want.

We'll take Av or A depending on Canon or Nikon abbreviation for aperture priority. You set your aperture and the shutter speed is matched according to the light and scene around. The flash is then set according to the prescribed rules of the program that the camera is working to. You get a result. You can still over ride BOTH camera and flash if you don't like the result.

Leave your Av or A set. Leave your aperture as you wanted. If you want the overall scene a bit darker then dial in a bit of - exposure compensation ON THE CAMERA. What you are saying, in shorthand, is :
Camera, I need the overall amount of light down a bit. This works without flash or with it. On Nikon, this reduces the overall final result, so the flash gets turned down a bit too so the whole picture goes darker.

If you want to light your flash subject a bit brighter dial in some + flash compensation (probably on the flash itself). This leaves the overall scene as it is, a bit dark. It then punches a bit more flash in and so lights the bits hit by flash a bit brighter.

You can do it the other way round too, by making the flash less and the camera light more....depending on WHAT YOU WANT. Take control of your pictures, don't leave it to the camera to do your thinking for you. It can't, it can only do what it is told - on all auto that is what it has been told to do by the little men in Japan, who have no knowledge of who or what you are taking a picture of, or the situation you are doing it on. So how the hell can they possibly know what exposure to give it? They don't, they just guess a middling value and in the main people accept it as being how it should be.

Go and work out what light is doing what to which bits in your picture.

The sun is lighting what?
The reflection from the glass window is lighting what? Look for it.
The flash will light what? Where is it pointing? How much power are you going to let it produce? How tight are you going to let it go?

Every picture you should be seeing this. That is what you need to develop, the ability to see where the light is coming from, the quality of that light (hard, direct in full sun - or softened and dappled through the leaves of the trees? Or just whats left that filters through under the underpass? Reflected soft light off the white wall of the big building opposite?)
You can choose this before you even start - how? Put your subject where you want them, facing the way you want the light to light them from.

Now, choose the result - is the available (ambient is just a word for the available light thatis there at the scene) light how you want it? Too much? Under expose it then - you have just turned the sun down! Try it, dial in -3 stops and just go and take a picture at midday tomorrow. It will be dark. Why? You turned the sun down! Even when it is raining, the sun is providing the light you see by. It is just the other side of the clouds and having to fight its way through the rain clouds, so not much is left, but it has still come from the sun.

Now, the other light you are going to introduce is from your flash - it is seperate to the sun. You can do the same thing, turn it up, or turn it down......independently of the sun, to get the result you want.

I think if I say anymore I will probably confuse myself!

 

[philthejuggler]

Lensflare - there's lots of interesting info and valid points in your post, but one point in particular goes against my practical experience and this has been mentioned above - if I have a dark background then a negative Fec seems necessary - presumably because it realises that most of the scene is dark and it pushes out too much flash to compensate - result is subject is overexposed on even 0 Fec.

Phil

 

[Lensflare]

Juggling Phil,

I take your point - but I have said you need to take control and make the things do what you want, not accept what they give you. That statement applies to your situation just as much as every other one.

"Now, even on TTL you can over ride the system and make it do what you want." Is what I actually said at one point.

Sometimes it is nice to have most of the frame dark and just one point of interest lit - makes for a very powerful image. Your auto systems won't do that for you, you need to make it do it. The same is true of when the meter is fooled by a very bright background too, just as it is with your very dark background. You have to take control, the auto will average it all out to grey - no bloody use to man nor beast, but a starting point from which to work.

Sorry if I wasn't fully clear enough. Thanks for putting me straight. Another Plymouth and tonic is required.

 

[philthejuggler]

Juggling Phil,

I take your point - but I have said you need to take control and make the things do what you want, not accept what they give you. That statement applies to your situation just as much as every other one.

"Now, even on TTL you can over ride the system and make it do what you want." Is what I actually said at one point.

Sometimes it is nice to have most of the frame dark and just one point of interest lit - makes for a very powerful image. Your auto systems won't do that for you, you need to make it do it. The same is true of when the meter is fooled by a very bright background too, just as it is with your very dark background. You have to take control, the auto will average it all out to grey - no bloody use to man nor beast, but a starting point from which to work.

Sorry if I wasn't fully clear enough. Thanks for putting me straight. Another Plymouth and tonic is required.

I guess it also reveals a bit about the approach to camera control - I tend towards using Av mode and adjusting EC / FEC to get the effect I want whereas others will always head for Manual - there's more than one way to skin a cat!

Phil

 

[Lensflare]

Either way, when the shutter speed and aperture are the same (the same regardless of hwo you set them - manually,or Av and exp +-) the result will be the same.

Like you. I use Aperture priority and run up and down the exp comp scale. It is faster than resetting on manual, but gives the same control, but only within 3 stops either side for any set aperture. Usually that is enough though. If it isn't it is a really whacky situation.

 

[Vertigo1]

Apologies for the thread resurrection but I have another question.

Been doing some playing and now have my head around the difference between exposing purely for flash and exposing for ambient and using fill flash. What I'm struggling with a bit is the area "in between".

Say I'm indoors but there is some ambient light. If I expose for ambient light and use fill flash then I get a very long shutter speed which I don't want. If I expose for flash then I end up with the typical "stark" flash result with the foreground strongly flash-lit and the background totally dark.

I ended up using full manual and experimenting with higher shutter speeds to try and balance the exposure for ambient and flash until I got a decent result. This was very trial and error though and I had to keep trying different settings until I got a result I liked.

I felt I must be doing something wrong here and there must be a better way of doing this. Any advice?

 

[tdodd]

If you bump up the ISO you will be able to achieve brighter backgrounds as well as keeping the shutter speeds shorter. The flash will also have less work to do, which will mean shorter recycle times and less risk of overheating.

Alternatively (or as well), bounce the flash off ceilings/walls so that as well as lighting your subject the room also picks up some light from the flash. Indeed, where possible, bounced flash is usually prefered indoors.

Examples....

Manual exposure without flash to show just how dim my ambient exposure was. This was at 1/60, f/4, 800 ISO. This remained the same for all shots that follow....

Of course, if I'd opened up tp f/2.8 and upped the ISO to 1600 the background (and my subject) would have been a lot brighter and the flash would have had little to do when I included it.


Direct flash (yuck)....

Flash bounced directly off the wall/ceiling close behind me....

Flash bounced off wall over my left shoulder....

Stofen Omnibounce aimed straight up....

 

[Vertigo1]

Interesting examples, thanks.

The specific situation I was in had a larger group of people stretching further into the background and I was having issues trying to adequately illuminate the farthest subjects using the flash so I was trying to use more of the ambient light.

If I exposed for flash, I'd end up with bright foreground subjects and dark background ones, yet if I switched to Av and thus fill-flash, the shutter speed plummeted to the point where camera shake would have been too much of a problem. I therefore switched to manual and raised the shutter speed to around the 1/20th mark to try and mix the ambient and flash light sources a bit. Just not sure if I was doing the "right" thing here or if there's a better technique in such circumstances.

 

[tdodd]

Your choices are to bounce off the ceiling to light up the whole room, and use a small bounce card to throw a little light forward onto your subject to fill in shadows in eye sockets and under the chin, and/or bump up the ISO. Slowing the shutter won't really work well with live subjects, unless you are deliberately aiming for a creative blur effect.

Look at what a single 580EX can do when it comes to lighting up an entire gym....

http://photography-on-the.net/forum/showthread.php?t=451770

I see you have a 430EX but you might be surprised what these flashes can do when used to maximum effect.

 

[HoppyUK]

Interesting examples, thanks.

The specific situation I was in had a larger group of people stretching further into the background and I was having issues trying to adequately illuminate the farthest subjects using the flash so I was trying to use more of the ambient light.

If I exposed for flash, I'd end up with bright foreground subjects and dark background ones, yet if I switched to Av and thus fill-flash, the shutter speed plummeted to the point where camera shake would have been too much of a problem. I therefore switched to manual and raised the shutter speed to around the 1/20th mark to try and mix the ambient and flash light sources a bit. Just not sure if I was doing the "right" thing here or if there's a better technique in such circumstances.

Edit: crossed post with Tim, but I think we're saying the same thing.

Sometimes there is no perfect solution and you have to compromise to get the best overall result. That sounds a bit like the situation you had.

The problem with the ambient light is that it's too low. To combat that as best you can, raise the ISO and use a lower f/number. Doing both these things should raise your shutter speed to a reasonable level.

The flash problem is that you have subjects both close and more distant. The inverse square law says that light falls away at the rate of one quarter (two stops) for every doubling of distance, so if you have close subjects one meter away that are correctly exposed, then two meters away they will be two stops darker, and four meters away they will be four stops down - effectively black.

The first thing to do is arrange the subjects and the position of the flash so that they are as equi-distant as possible. Using a remote gun is obviously helpful here; the position of the camera is irrelevant as far as exposure is concerned.

To reduce the rate of fall off, you need to increase the flash to subject distance so that the distance between near and far objects is minimised, relative to the overal distance. The way to do that is with bounce flash off the ceiling and/or a far wall, which means that the flash distance is now from the flash to the ceiling/wall and then to the subject, rather than straight to the subject.

There is a double benefit here as bouncing the light will also spread and soften it. Bounce flash uses a lot of power but since you have already upped the ISO and reduced the f/number, you should have enough power to fill even a fairly large room.

The only thing you need to do then for best result is to gel the flash so that it is as close to the ambient light in colour as you can reasonably get, then do a custom white balance. It has to be custom when bouncing as unless the ceiling/wall is clean white you will get an unknown cast from that. Of course you can always sort the final colour in post and to make that job easier if you can do a test pic with a grey card in shot to use as a reference in processing that will be easy and accurate, but you still need to gel the flash.

 

[Humpty]

Really interesting thread. Thaks for all the comments, it has really helped my understanding of flash use.

 

[Vertigo1]

Back again...

Manual exposure without flash to show just how dim my ambient exposure was. This was at 1/60, f/4, 800 ISO. This remained the same for all shots that follow....

I presume these settings were on manual? As you non-flash shot demonstrates, if the camera had been on aperture or shutter priority then a far lower shutter speed would have been selected so I presume you put it on manual. If so, two questions...

1. What made you select these settings in particular?

2. When using the flash in TTL mode, can I just set the exposure manually and expect the flash to automatically provide the correct amount of light, via TTL metering?

 

[tdodd]

1. I nearly always shoot with manual exposure and especially when using flash. For this series of test shots I wanted to make sure that my ambient exposure was low so that the position/size/quality of the flash shadows was very obvious. I shot these test images so that I could figure out what sort of approach gave the most pleasing results in this type of situation. It alerted me to problems with something as simple as a Better Bounce Card when making it too large and having it off to the side.

2. You can absolutely set a manual exposure for the ambient light. Usually this would be at a level that was just slightly underexposed. Flash will then top up the exposure and give some pop to your subject. Alternatively you can dial down the ambient exposure and make the flash work much harder. That way you can overpower any oddities in the ambient lighting such as a variable colour temperatures or nasty lighting like fluourescent lamps. As for ETTL, it is subject to the same difficulties as normal non-flash exposure metering. If you put a dark/black subject/scene in the frame the flash will try to bring up the exposure to make it look grey. If you put a bright/white/light subject/scene in the frame the camera flash will underexpose, again in order to make a greyish tone. Therefore you need to interpret the scene yourself and adjust the FEC in just the same way that you might dial in some EC for the ambient exposure. Sometimes you just want to provide a little fill, rather than using the flash as a main light source, so you would then dial the FEC down quite a bit - possibly 2 stops or so.

Neil van Niekerk explains these things very well on his website - http://www.planetneil.com/tangents/flash-photography-techniques/

 

[Vertigo1]

Well from what I've seen, some people prefer to use full manual whilst others tend to use Av mode. What I can't wrap my head around is how Av mode works at all.

If I'm in a low-light situation and select Av then the camera will meter for the ambient light. As there isn't much of this, I'll usually end up at the max aperture of the lens with a very slow shutter speed, these being the settings required to achieve an adequate exposure with the ambient light.

The problem is that the flash is going to "fill in". Surely leaving the settings correct for only ambient light and then having the flash fire is going to result in overexposure?

Take an example. Say I'm indoors with poor lighting and, metering in Av mode for ambient light gives me 0.5s at f/2.8 at ISO400. If I took this shot at those settings without flash, I'd get a good exposure, although I'd obviously have to hold the camera pretty damn still and hope the subject wasn't moving!

Now add flash into the equation. If I remain in Av mode, then the exposure would be as above. When I take the shot, however, the flash will fire so surely I'd end up with an overexposed image? What I want to do is take advantage of the fact that the flash will provide additional light to allow me to raise the shutter speed significantly. This is the situation in which I couldn't see how Av/fill-flash mode could possibly work and thus switched to manual and started "messing about" a bit.

 

[david1701]

Well from what I've seen, some people prefer to use full manual whilst others tend to use Av mode. What I can't wrap my head around is how Av mode works at all.

If I'm in a low-light situation and select Av then the camera will meter for the ambient light. As there isn't much of this, I'll usually end up at the max aperture of the lens with a very slow shutter speed, these being the settings required to achieve an adequate exposure with the ambient light.

The problem is that the flash is going to "fill in". Surely leaving the settings correct for only ambient light and then having the flash fire is going to result in overexposure?

Take an example. Say I'm indoors with poor lighting and, metering in Av mode for ambient light gives me 0.5s at f/2.8 at ISO400. If I took this shot at those settings without flash, I'd get a good exposure, although I'd obviously have to hold the camera pretty damn still and hope the subject wasn't moving!

Now add flash into the equation. If I remain in Av mode, then the exposure would be as above. When I take the shot, however, the flash will fire so surely I'd end up with an overexposed image? What I want to do is take advantage of the fact that the flash will provide additional light to allow me to raise the shutter speed significantly. This is the situation in which I couldn't see how Av/fill-flash mode could possibly work and thus switched to manual and started "messing about" a bit.

for all intents and purposes the two exposures are separate, you'll also find the camera won't go to a shutter speed lower than 1/60 if there is flash involved

 

[tdodd]

Vertigo,
The camera will moderate the flash to prevent overexposure. If your ambient exposure is quite dim the camera will add a lot of flash power to bring the levels up If the ambient exposure is quite bright the camera will only add a little flash, just to top up the exposure.

However, there are two main ways of using flash that affect your approach - direct flash vs bounced flash. If you use the builtin flash, or a Speedlite aimed straight at your subject then the subject will get blasted. It won't be overexposed, because the camera will control the flash output, but due to the inverse square law of flash falloff the background will not get much illumination from the flash at all. Therefore the camera, left to its own devices (Autoexposure), will try to expose the ambient scene almost correctly, which may well result in long exposures, and the flash will just brighten your subject to improve "pop" and to put catchlights in the eyes.

Note, if you use Av mode then the camera will drop the shutter speed as low as necessary in order to get a (roughly) correct ambient exposure, and this can catch a lot of people out. I found out the hard way when I shot my first ever wedding (a freebie for a friend, while I was also a guest) and used a Speedlite for the first time. I couldn't believe I was seeing such long exposure with flash enabled. It was a real head scratcher. This thread started my journey to salvation - http://photography-on-the.net/forum/showthread.php?t=286091. Now I know better. You can adjust a custom setting to force the shutter speed to 1/250 in Av mode on the 40D. IIRC you get more options from the 50D and later. Personally, rather than be limited to whatever options the camera gives me in Av mode I just shoot manual and have things the way I like them.

The alternative approach is to use a Speedlite and to bounce the flash light off the ceiling and/or walls. When you do this the flash is going to light up the whole room as well as your subject. In this scenario you do not need a long exposure to bring up the ambient levels. The flash will light everything. If you were to shoot in Av mode the camera would still try to make the flash a fill light instead of a main light, so the shutter speeds may well be very slow and you could end up with blur/shake even though you were using flash. What you need to do is to take more control over the ambient levels, dialing them down a bit to get more agreeable shutter speeds. Then the flash will do the rest.

For example, I've shot a few weddings and flash use is commonplace indoors. Direct flash looks pretty awful, so bounced/diffused flash is the way to go. I will usually set a manual ambient exposure of something like 1/60-1/100, f/2.8, 1600 ISO. That is not enough to get a good exposure so the flash has to finish the job. However, at least I will have some ambient light coming in so I at least pick up some of the mood of the scene and the background does not drop off to pitch darkness.

Here's a typical example shot with my 30D at 1/60, f/2.8, 1600 ISO. It isn't perfect but hopefully you can see that I have a reasonable balance in subject lighting with the background.

The thing is, once I have my manual exposure set up for the ambient I can leave my setting like that all night long. My ambient exposure won't get thrown off by disco lights, wall lights, a sea of dark suits, the frame nearly filled by a wedding dress etc.. Within such a scene the ambient lighting does not vary too much. Sure there a re hotspots, but I want the camera to ignore them. Then all that remains is for the flash to earn its keep with ETTL exposure. But like I said, the flash can be fooled by a predominance of dark tones or light tones. The flash is aiming for neutral "grey" so you will need to wiggle the FEC a little from time to time.

Here's another example, this time in daylight so my ambient exposure was very different, but I needed flash because my subject really was poorly lit. EXIF is 1/250, f/2.8, 800 ISO. Flash was bounced/diffused.

Last one, this time with some punishing differences in light levels due to the lights directly in the picture behind the bride. EXIF is 1/60, f/3.5, 3200 ISO + bounced/diffused flash....

Do read Neil's tutorial. I am a beginner in flash and he is a God. Go and see what he says.

 

[Vertigo1]

Thanks. It does seem that you're confirming what I already thought with regards to manual exposure, in that you set it such that the ambient light contributes to the scene but the flash still has to contribute the rest or majority of the light.

What I still can't wrap my head around is how Av/fill-flash mode works at all as using this mode will set the exposure for ambient light only, producing a very slow shutter speed. The flash can't adjust its output to cope with this situation as the exposure assumed no flash at all so any light it produces would be "too much".

Your third paragraph would seem to suggest you've experienced this very effect which just adds to my bemusement about how fill-flash ever works indoors.

 

[tdodd]

If you are getting overexposure it sounds to me like you have a setting wrong somewhere, or the flash is not connected to the camera properly and they are not communicating as they should. The camera should easily be able to suppress the flash output to suitable levels. Can you post an unedited example with EXIF intact?