low light flash and background light

[samester]

hi,

i'm happy with most of my flash work so far but the one element that i still find a little inconsistant is when trying to flash a subject late afternoon handheld using the D70 and SB800.

the ambient light exposure might be say 1/40 at f3.5 ie there's still enough light so that the shutter speed is important in controlling camera shake when flashing the subject handheld.

an example of what i was trying to achieve was at a late afternoon graduation ceremony, sun has just set and one of the graduates is holding their graduation certificate about 30-40cm in front of them

at the moment i usually switch to manual, shutter anywhere between 1/60 and 1/125 depending on potential for camera shake given the ambient exposure and aperture is f9 or f11 to get decent depth of field in order to have the graduation certificate and the graduates face both sharp - a little flash comp and the subjects come out looking good but the background is dark (looks like it's night time when it's about 6:50-7pm)

in order to get some of the background light, do i need to compromise depth of field ?

not too sure how to best flash a subject when the light is low but there's still enought light around to utilise both the ambient and flash light.

any ideas ?

thanks,
sam

[shutterbug]

Hi Sam,

n order to get some of the background light, do i need to compromise depth of field ?

Short answer is yes....open your lens up to get max light, also increase your ISO. Are you using a fast lens?

vince

[gstark]

Don't forget that the D70 will synch with flash at any shutter speed, if you know how to do it.

But that gives you a great deal of flexibility. You can set your aperture as you need for the ambient light (background) exposure, and set your shutter speed to match. Then set your flash to, say, the same aperture with -0.7 FEC.

Alternately, set your exposure to underexpose the background by around 0.7 or 1 stop, and then set your flash to the aperture that you now have dialled in.

Either of those approaches will work fine, depending upon the end result that you consider more desirable.

[samester]

Hi Sam,

n order to get some of the background light, do i need to compromise depth of field ?

Short answer is yes....open your lens up to get max light, also increase your ISO. Are you using a fast lens?

vince

hi vince,

i do have fast glass but i really don't want to compromise DOF ie i want the student and the certificate tack sharp - that often means shooting f5.6 or smaller, i often aim for between f9 get the best out of the lens and also for greater DOF.

opening right up wont give me sharpness in the subject and also something that they're holding up about 30cm in front of them - unless of course there's something in my technique that is wrong - i'm focussing on the certificate and adjusting aperture to ensure person 30cm behind is in focus also.

[samester]

Don't forget that the D70 will synch with flash at any shutter speed, if you know how to do it.

But that gives you a great deal of flexibility. You can set your aperture as you need for the ambient light (background) exposure, and set your shutter speed to match. Then set your flash to, say, the same aperture with -0.7 FEC.

Alternately, set your exposure to underexpose the background by around 0.7 or 1 stop, and then set your flash to the aperture that you now have dialled in.

Either of those approaches will work fine, depending upon the end result that you consider more desirable.

hi garry,

i think if i set the aperture to exposure the background light i'll need to open the lens up which will compromise DOF. sync speed isn't a prob either (at least i haven't noticed it to be a prob).

the outcome i am after is a wide DOF to allow a couple of objects, one about 30cm in front of the other, to be tack sharp - i'm shooting about at about a metre (or two at most) away and handheld. ideally if there's a little of that wonderful late afternoon glow in sky after the sun has set, i don't want the background skyline to come out underexposed.

i think the prob is that to retain some of the ambient light i need to open up and compromise DOF - either i can't have my cake and eat it too or there's something lacking in my technique

[gstark]

i think if i set the aperture to exposure the background light i'll need to open the lens up which will compromise DOF

Not necessarily. You can slow down the shutter speed to get the same EV, and any shutter speed down to 1/25 won't (or shouldn't) present too many issues for you.

i think the prob is that to retain some of the ambient light i need to open up and compromise DOF - either i can't have my cake and eat it too or there's something lacking in my technique

F/8 of f/11 should be readily doable by adjusting your shutter speed to match - or be within one stop of - the settings for the ambient light.

If there's not enough light to permit that combination of settings ... then yes, you're hosed - but again, and as Vince suggested, a slight nudge of your ISO might just be the key.

[samester]

i think if i set the aperture to exposure the background light i'll need to open the lens up which will compromise DOF

Not necessarily. You can slow down the shutter speed to get the same EV, and any shutter speed down to 1/25 won't (or shouldn't) present too many issues for you.

there's still quite a bit of light about and my hands mustn't be all that steady because i seem to get a little camera shake hand held at anything less than say 1/60.

i think the prob is that to retain some of the ambient light i need to open up and compromise DOF - either i can't have my cake and eat it too or there's something lacking in my technique

F/8 of f/11 should be readily doable by adjusting your shutter speed to match - or be within one stop of - the settings for the ambient light.

If there's not enough light to permit that combination of settings ... then yes, you're hosed - but again, and as Vince suggested, a slight nudge of your ISO might just be the key.

i think that i'm probably hosed, there's a little light around but not really enough to give me any kind of background or amient light exposure.

thanks,
sam

[gstark]

i think if i set the aperture to exposure the background light i'll need to open the lens up which will compromise DOF

Not necessarily. You can slow down the shutter speed to get the same EV, and any shutter speed down to 1/25 won't (or shouldn't) present too many issues for you.

there's still quite a bit of light about and my hands mustn't be all that steady because i seem to get a little camera shake hand held at anything less than say 1/60.

Ok .... this does come down to technique, and a bit of practise.

If you're younger than I am, you should be able to regularly handhold at 1/30 (easy) and frequently at 1/15.

In the right location, slower speeds are possible too.

How are you holding the camera?

Body in your right hand, left hand should be cradling your lens (palm up), on the zoom and/or focus ring. Elbows should be in, arms held against your sides/chest.

Breathing should be even. Inhale, exhale, inhale, hold, squeeze your shutter release, exhale.

Some people prefer to exhale, hold, squeeze, and that's ok too: whatever you find works best for you is fine.

And when I say squeeze the shutrter release, that is exactly what I mean, and it's vitally impaortant that you do exactly that. DOn't jab (I'm sure that you don't) but do make it as smooth a movement as you can.

And if there's something you can lean on - a tree, a wall, whatever, then don't be afraid to use it.

MAybe you can prop your elbows on a tree branch or a fence, and then form a tripod using your arms (on that support) and your body.

Practice those techniques a bit (ok, a lot) and see what sort of shutter speeds you can get yourself down to. It takes practice, but it's not difficult.

[MattC]

Hi Samester,

What you have described sounds like it is simply fill flash - the sort where the entire scene is evenly lit and a little flash is desirable to get some seperation between the foreground and background. ie "pop".

The camera setup that I use when flash is attached is manual mode, spot meter, TTL (SB800), AE/L to FV Lock, ISO as required. It does not matter if I am indoors or outdoors. These settings are constant throughout this post.
The scene that you described is probably one of the easiest to spot meter. Skin is fairly close to neutral - give or take. Very fair skin when spot metered might be as high as +0.3, dark skin as low as -2/3. A reasonable understanding of tone vs EV is the only requirement.
I prefer the techniques I mention here because they put me in control instead of having to second guess what the technology is doing. I have copped a little flak in the past for these techniques but, if nothing else, it helps in understanding exposure, and provides a means for dealing with problem shots.

The method that I use for fill is to set exposure compensation on the flash for the subject (tone being metered) and use a shutter speed, aperture, ISO combination that is 0.3 - 0.7 EV below the flash value - I call that fill value, which is just the difference between ambient and flash values. Subtract the fill value from the flash EV. If the flash value is +0.3 and my fill value is 0.7 then 0.3 - 0.7 = -0.3. The -0.3 value is the VF meter reading in manual mode. The metering point for both flash and ambient is exactly the same point - this is important especially with smaller fill values.
The technique goes, dial in FEV, focus on metering point (skin), dial in aperture/shutterspeed as described above, FV Lock, focus on focus point (eyes?), recompose and shoot. If your shooting conditions do not vary (biggest variable here is likely to be distance to subject), you can use the same settings through a series of shots. Just keep an eye on your exposures - if the sun is setting keep an even closer eye on things.

Fill values of more than 1.0 will result in significant darkening of the background, which may be okay for effect, but is not what you are after in this case.
When small fill values are used up very close, the SB800 may overpower the exposure even though it is firing at minimum power. If that happens, use the diffuser dome with the head up one click. That will effectively drop your flash output by a couple of stops and put the flash back into a usable range.
I am yet to find another way of using this technique in other modes effectively... Part of the problem is the lack of an extra program button on the D70. Manual mode is the only way to lock the ambient exposure if FV Lock is used, and it is pretty hard to avoid that one from a compositional POV.

If you can get a shutter speed, aperture and ISO combination that will work without flash (or within 2/3 stop), this technique will work for you.

You also mention capturing the after glow of sunset. If the after glow is brighter than your subject, you'll need to reduce the ambient exposure. Easy to do (in theory) by spot metering the background highlights. If those highlights meter at +2 or more then they are likely to blow. Reduce ambient exposure accordingly. This really is getting away from fill flash and into high contrast flash techniques. Also be aware that near background (that between your subject and the afterglow) may be darker making the shot look like a flash shot. If possible... try to set the subject against the sky only.
The technique is, FEV for subject, meter background and dial in appropriate ambient EV, focus on metering point, FV Lock, focus on focus point, recompose and shoot. It is likely that the FEV will be something like 0 - +0.3 for fair skin and the VF meter reads +1.7 on the brightest highlights (that may still be too bright for a natural looking balance after the sun has set). With a good understanding of tone vs EV (and some practice) it is possible to balance background exposure against foreground exposure in such away that the exposure appears seamless or with just a little bias towards the foreground. The worst thing that can happen here is that the foreground is underexposed.
If the afterglow is too dark then you are out of luck.

Sorry about the long explanation... but it is the short version... honest!

Cheers

[Matt. K]

Simple answer is use the slower shutter speeds and work from a tripod.

[jerrysk8]

light meters do wonders. i could never live without my L358.

[samester]

Simple answer is use the slower shutter speeds and work from a tripod.

yep that would work but i'm shooting handheld!!

[Matt. K]

samester
Then your only other option is to use very high ISO's and give away technical quality. There ain't any other way.