metering for manual flash and softbox « Neil vN

Tangents

metering for manual flash and softbox

May 18, 2009

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.

Here is the result. (Also check the posting on the Nashville workshop.)

The lighting is simple – the softbox is held to the my left-hand side in this instance. The colors 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.

This time I wasn’t quite at maximum sync speed (1/250th for this camera) since I was working in the shade, and not in very bright light. But the moment I work in bright light, using flash, it makes the most sense to be at maximum flash sync speed, and figure your settings out from there.

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?

33 Comments »

Hi there again Neil,

Thanks for the info again. So nice to know how this kind of shot is done practically speaking.

Could you have used a shoot through umbrella for this shot, or is a softbox the best option?

Comment by Rory Mole — May 18, 2009 @ 2:38 am
Rory, using a shoot-through umbrella outside would’ve meant too much light from the flashgun would’ve been lost.

A fair amount of light reflects from the shoot-through umbrella. Inside a room, this doesn’t mean as much light is lost as outdoors, because the reflected light usually bounces off walls and ceilings and spills back again on the subject.

Therefore a shoot-through umbrella wouldn’t have been nearly as efficient as a softbox which contains the light better.

Neil vN

Comment by Neil — May 18, 2009 @ 5:21 am
Hi Neil,
Thanks a lot for the explanations! I love the difference between with and without flash. With flash it just looks so smoother and more professional.

Two points from my side:
- Is manual flash also influenced by zoom head setting?
- You could also set flash power just approximately in the correct region and then find the correct aperture to get the correct flash exposure, thereby leaving the ambient exposure (e.g. aperture+1/2 stop, shutter -1/2 stop). Did you have any reason for not doing this? Or was it just convenient enough to let the “flash holding person” increasing/decreasing the power?

Looking forward to your next posts,
Martin

Comment by Martin Burri — May 18, 2009 @ 7:06 am
Martin, yes, changing your zoom head would affect the effective power of your speedlight.

(I’m not quite sure what you’re asking in the 2nd question though.)

Neil vN

Comment by Neil — May 18, 2009 @ 9:23 am
Hi Neil,

Great article explained in an easy to digest manner. Am really looking forward to your workshop in Ireland later this year.

A quick question, if I may, on using an incident meter, such as the L-358, in ambient light such as in this case. It’s something that has been the topic of much debate on forums the world over, but in most cases the discussion relates to using it in a studio environment. The question is simply, what is the correct direction in which to point the lumisphere when taking your ambient light reading – from the subject back towards the camera or from the subject back towards the light source?

Whilst I’ve had great success in using my L-358 in the controlled environs of the studio, using it outdoors is a different matter and I often end up with under-exposed results, particularly on bright days, unless I retract the lumisphere or shade it from the brightness of the overhead sky.

Oh, by the way, this blog just keeps getting better and better!

Thorsten.

Comment by Thorsten — May 18, 2009 @ 10:25 am
Thorsten, I generally have the dome retracted when I meter for ambient light, because the light from the sky does seem to inflate the meter reading.

But I never rely exclusively on a hand-held meter .. in fact, I mostly rely on the histogram. So even with metering with a hand-held meter, I would still sway my settings depending on the histogram and blinking highlights, and how bright the image appears on my LCD.

All of these things should converge to a point where you have correct exposure.

But even then, I would rather not get bogged down to the n-th parsing of the exposure metering methodology. I would want it close enough .. really close .. but still try to keep a rhythm to the shoot.

Rather work with your subject .. get a sequence of images .. and work towards actual Photography. Rather than minuscule adjustments. Even more so … get the image, rather than argue about minuscule adjustments and differences in metering technique on the forums. ;)

Oh, and as for how I point the flashmeter … at an angle halfway between pointing it at the main light source, and the camera position. And even then … I will adjust my settings so that what I see on my histogram and LCD display, looks good. And then I still adjust my RAW image in post-production.

Meter technique is one of those areas where great skill and technique is immensely valuable .. but shouldn’t interfere with actual picture-taking. (If that makes sense?)

Neil vN

Comment by Neil — May 18, 2009 @ 11:00 am
Hi Neil,
Sekonic gear question: Is this the Transmitter module that you install into the Sekonic?

Comment by Stephen — May 18, 2009 @ 11:19 am
Stephen, that is the exact module that I use in the Sekonic L-358 that triggers the PocketWizard slaves. It makes life easier since it means one less thing to hold in your hands, or one less cable to hook up.

Neil vN

Comment by Neil — May 18, 2009 @ 1:40 pm
hallo neil,
some questions:
why did you underexpose the ambient light for one stop?
Would it not be different when metering off her white shirt and go down minus one stop OR metering on the bricks and than go down by one stop?
Ah I see, metering the light with the sekonic is different than metering “the reflected light of bricks or white shirt”.

“If we hold our softbox too far away, then the light progressively becomes harder.”…does that mean that YOU (or the person that takes the picture) is holding the softbox?…means far away from HIS body?
than it is right.
but if the assistent will hold the box too far away (in relation to the model)…than it is wrong, because the light will go softer.
as far away the softbox…as softer the light.

“then we need to adjust the power to where we get f5.6″…can you not select the aperture and iso on your flash in man. mode?
on my FL-50 i can select ISO and Aperture or the power ratio…..1/64, 1/128, 1/2, 1/4…and so on….

thank you for sharing a new lerning lesson.
peter

Comment by olympus_fotograph — May 18, 2009 @ 3:58 pm
Peter, I purposely under-exposed the available light by a stop because I wanted the flash to add the additional light. As you can see in the comparative images, using the softbox flash like that does radically affect the final image .. and that is the look that I was after.

In theory, under-exposing the bricks by a stop, and under-exposing the white shirt by a stop .. should be the same exposure. (In theory), they shouldn’t mean a different choice of settings.

When I said the “if we hold the softbox closer”, I meant it as a general “we”. I didn’t hold up the softbox. My assistant did. And my assistant would bring the softbox closer or further away from my subject.

As others mention here in subsequent posts .. don’t confuse brightness with softness.

Neil vN

Comment by Neil — May 18, 2009 @ 4:07 pm
olympus_fotograph,
Unfortunately, I must contradict your statement. “As far away the soft box from the subject as _harder_ the light” is the correct expression since the apparent light size gets smaller and smaller with distance from the subject. In infinite distance, the soft box gets a point source. So what is softer, big or small light? – Exactly: big light, which means soft box in short distance.
To help to understand, imagine how the light beams spread from the different positions from the soft box towards the subject: Light from the center hits the subject differently than light from the border of the soft box. Make a small sketch if you want to. And you will realize that the bigger the (apparent) light source, the more the light will “wrap” around the subject which is actually what makes it look softer.
Did you understand my explanations? Maybe Neil will find some better words, he’s talented in explaining such stuff.

Comment by Martin Burri — May 18, 2009 @ 4:25 pm
hello what i mean is visible here:
http://www.traumflieger.de/desktop/blitzreport/grafik_lichtausbreitung.jpg
so if the light is close to object—>> the light is hard.
if the light is far to object—> the light is soft.
which brings us to my question from what place neil is talking about the softbox.
“If we hold our softbox too far away, then the light progressively becomes harder.”…does that mean that YOU (or the person that takes the picture) is holding the softbox?…means far away from HIS body?…you can move the left hand fwd or aft.
than it is right.
but if the assistent will hold the box too far away (in relation to the model)…than it is wrong, because the light will go softer.
as far away the softbox…as softer the light.
grts
peter

Comment by olympus_fotograph — May 18, 2009 @ 6:25 pm
@olympus_fotograph:

If we start with the fact that we all know that the sun is bigger than any softbox we are ever likely to use, and yet we all know that the light of the sun in the middle of a bright cloudless summers day is just about as hard as you can get, then it should quickly become apparent that the reason the suns light is so hard is because it is so far away.

So, it’s not the actual size of the light source that matters, but the apparent size, relative to your subject. As you move your light source away from your subject, the apparent size decreases, just like if you are right up beside a car, it is big enough for you to get into, but if you walk away far enough, you could literally fit that same car between your thumb and forefinger if you hold them up and look through them at the car; the size of the car didn’t change, but because the distance between you and the car changed, the apparent size of the car changed.

The diagram you have linked to simply describes the inverse square law of light, which states that as you double the distance between the light source and what the light is falling on, you reduce the intensity of light where it is falling, by a factor of 4 (i.e., it becomes 1/4 of what it was at that point).

Comment by Thorsten — May 18, 2009 @ 11:41 pm
@Thorsten,
Thanks for extending my explanations.

@Olympus_photograph,
You must be careful to not mix up “soft/hard” light with “bright/dull” light. As Thorsten said, your image describes how the light intensity per square meter decreases with distance. What I meant with soft light is that the border between bright and shadow area on the subject is soft. With a point source this border is very small (e.g. 1-2 mm) and sharp – in other words hard. But the bigger the apparent light source, the wider this range becomes and we are saying soft light (e.g. 20-30 mm).

Comment by Martin Burri — May 19, 2009 @ 2:46 am
Hey Neil! Thanks for the great workshop in Nashville. I had already known a lot of what you covered, but putting it into action with the one-on-one tutoring by you really made everything sink in. I also discovered just how much my equipment is limiting me. Before the workshop my wife and I have been just getting by when it comes time to use flash, but now I think it’s time to make it a priority to update everything we have. There’s so much we’re missing out on by not using created lighting regularly. Thanks again and I had a great time meeting you in person!

Comment by Cory Ferguson — May 19, 2009 @ 12:17 pm
Cory, it was nice meeting you as well. And I hope the workshop helps to bump you up to another level in experience and technique. : )

Neil vN

Comment by Neil — May 20, 2009 @ 12:50 am
Hi Neil,

Thanks for this, I’m going out this weekend to shoot bridal portraits and I put together my version of a light on a stick with a softbox. It’s pretty stable but I could have sworn I saw an article or post by you using a pretty nice mount on top of your monopod. Is that article on your site? I’d really like to see again how you set yours up.

Comment by Gary Segler — May 22, 2009 @ 1:30 pm
Gary, here is the set-up that I use with the softbox and a speedlight. And I have just assembled the same for use with a Q-flash.

Neil vN

Comment by Neil — May 25, 2009 @ 12:49 am
Hi there Neil, I am a long time follower-first time commenter of your blog. My big question for you is this – Since this example is primarily an ambient light photo what do you set on camera as far as white balance goes? Do you just leave it in auto, set it to flash, or do some sort of custom white balance? Does really underexposing the background by like 3 or 4 stops affect what you would initially set the camera to? I am just so curious how you approach wb with off camera flash. Thanks so much Jason

Comment by Jason Malwitz — May 31, 2009 @ 9:45 pm
Hi there Jason ..

Here is an earlier post on how I choose WB settings.

In short, I primarily shoot with Daylight, Cloudy, Tungsten or 3700K white balance settings.

But I do shoot in RAW and then touch up the color temperature a bit as part of my regular post-processing workflow.

I don’t use custom WB settings, since, for me, it would slow down my rhythm during a shoot. But I have more slack here than a commercial photographer would, so I think this decision is very much based on the kind of precision your photographer requires.

I generally don’t use Auto WB, since I would rather not have the WB change from image to image. It is faster to edit sequences of images … and I’d rather have a group of images have the same not-quite-correct WB than have them have different colors. This way I edit groups of images instead of individual images.

For this image, (and most times when I use flash), I start off with Cloudy WB. On my Nikon D3 bodies, I have dialed in B1 on the Cloudy setting, to make it a touch colder than they have it as the default.

All of this just points to it not being necessary for most photography, to get too stuck on precise WB.

Neil vN

Comment by Neil — June 2, 2009 @ 2:09 am
[...] Before we get there, just a note about the lighting. It was the same light as I used in this previously posted photograph of the NYC photo shoot-out. The lighting set-up was similar to the one mentioned here, where I explained some of the metering involved in using manual flash with a softbox. [...]

Pingback by tangents » NYC photo-shootout redux — June 18, 2009 @ 11:13 pm
Though the example with flash is more dramatic, it looks as if flash has been used. Not just that it’s a little hot.. which is easily corrected even in LR or PS.. but also because the light starts to taper off at the top. With tall backgrounds there will be limits to how far a soft box can reach. Other than dodge/burn what can be done, if anything, if move the box further away (to reach higher) doesn’t light the subject as desired? A reflector could be utilized opposite the box, but I don’t see where to put it in that situation out of view.

Comment by Ken — April 11, 2010 @ 12:07 pm
Ken … I’m not sure that is a problem per se – that the light tapers off to the edges of the frame. In fact, I like that slight ‘hot-spot’ look to it.

The solution around it is to use multiple lights and really add as much as you need, in every part of the frame. But this then becomes a much larger production, and you lose the ability to move easily from one spot to another.

Neil vN

Comment by Neil vN — April 11, 2010 @ 1:01 pm
Neil..great work and explanations!

Can I ask about setting the manual flash. I have a 550EX speedlite. It wouldn’t be dedicated to my camera, so I would set the flash manually. You mentioned setting the flash to a power output that would register 5.6 when read with a meter. If I had to set this are you just dialing in say 1/2 power and taking a meter reading to see where you’re at. I can’t set my ISO and F.stop in this mode.

If I shot in ETTL, do I set my flash settings to match my camera settings and then dial in FEC?

Thanks

Comment by Julian Hough — June 5, 2010 @ 5:39 pm
Hi there Julian .. you seem a little lost. :)

With E-TTL, your camera and flash will follow your settings. In other words, as you change your aperture and ISO, your camera and flash will work together to give you correct flash exposure (Within reason of course.) You then change your FEC to have more or less flash than the camera thought you need.

So it isn’t quite as you have it there: “do I set my flash settings to match my camera settings”. That is how manual flash would work. Not TTL.

Back to the first part of your question. Your 550EX should be dedicated to your camera if it is a Canon D-SLR. What camera do you have?

And with manual flash, this is exactly what you would do … you would set your ISO and aperture on your camera. You would set the ISO and aperture, based on your ambient light, and what you want to do with your manual flash.

Neil vN

Comment by Neil vN — June 6, 2010 @ 7:59 am
Neil,

I am lost it would seem! I am aware that the flash and camera in E-ttl mode are communicating – it must have been the long night! :)

I am practicing shooting portraits with some loaned equipment and was trying to learn setting up an off-camera flash with my Canon 40D. There’s no transmitter involved, so camera and flash would be set manually.

My confusion, or clarification, is once the exposure is set without flash for the ambient (-1 stop)light, do I then set the flash power to 1/4, or 1/8 to begin and adjust as necessary to match the lightmeter’s suggested F-stop.

If it’s that simple, then I obviously had been over-engineering it :)

Your posts are great, and I appreciate the feedback!

best,

JH

Comment by Julian H — June 6, 2010 @ 12:50 pm
When you say there is no transmitter involved, are you using the camera and speedlight in wireless mode?

My confusion, or clarification, is once the exposure is set without flash for the ambient (-1 stop) light, do I then set the flash power to 1/4, or 1/8 to begin and adjust as necessary to match the light meter’s suggested F-stop.

ok .. let’s take it a step back.
You have your ambient exposure, and it tells you .. for example:
f5.6 @ 100 ISO (at whatever shutter speed, no higher than max sync speed)

Then you take it to f8
It seems that is what you’re trying to do there with the (-1 stop) comment?

ok .. so you now want f8 at100 ISO from your manual flash.
You have a few ways of getting there.
1. You can use your flashmeter, and dial your flash’s power (1/2 or 1/4 or 1/8) until you get f8.
2. You use your histogram in the same manner.
3. You can guess, take a shot, and look at your LCD preview. Repeat until you like what you see. It’s a clumsy method, but will get you there, but not with as much accuracy as the other two methods.

It’s that simple. : )

Neil vN

Comment by Neil vN — June 6, 2010 @ 1:00 pm
“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″

Hi Neil, As usual great site great info. Quick question on the above comment. I am trying do some amateur studio work and I am using two SB-800′s, one bounced into a Westcott Softbox (the umbrella style that requires no speed ring) and the other into an umbrella. I’m getting inconsistent exposures with TTL everytime I recompose or change from landscape to portrait format so I am trying to switch to manual flash to increase the consistency of my exposures. Here’s my question. When I’m using the 800′s in wireless mode triggered by the my camera (no Pocketwizard) I then have no aperture reading from the flash only the ratios as the appear on my D200′s menu. So in that case how do I determine my aperture setting? Can’t really uses the GN method because the flashes are both being bounced in to their respective light modifiers. Don’t have a flash meter either.

Sorry for the long winded question and thanks again for a great website.

Ross

Comment by Ross K. — September 29, 2010 @ 1:51 pm
Ross, that would be a typical problem with TTL flash – the change in exposure as you change your composition. Manual flash is the best option when you’re working in a static set-up, especially in the studio. Metering is then best done with a flashmeter. So that’s the good news .. you’re going shopping!

Neil vN

Comment by Neil vN — September 29, 2010 @ 1:53 pm
Hello Neil,

I’m not sure if you’re still answering questions posted on this page, but hopefully so…

I’m baffled by your suggestion that, after metering for ambient and dropping exposure by 1 stop (from f/4 to f/5.6 in this case), you’d then go attempt to get a manual flash reading of f/5.6. Why not f/4?

To my way of thinking, this would be tantamount to dialing in -1 FEC if you’re going the ETTL route, which I don’t think you’d do unless there was a specific reason to do so. When I’m shooting with ETTL flash, I’ll manually determine ambient exposure, drop exposure by 1 stop or so, and then default to +/- 0 FEC unless scene reflectivity is an issue one way or another.

So my gut tells me than when using manual flash, you should meter for ambient, drop exposure by 1, then adjust flash power/distance until your flash meter gives you the aperture that was originally suggested as correct in the original ambient metering step. What am I missing here?

BTW, I bought your book on off-camera flash, and I love it.

Good day!

Dave

Comment by David D. — January 27, 2012 @ 3:41 pm
Dave,

The metering of f4 to f5.6 so the ambient light is one stop under-exposed is no problem, that’s how he wanted to have the ambient, so far that’s easy.

Now, the explanation of why you then meter the flash to f5.6 is because that’s his current f-stop, 5.6, therefore he must have the flash metered to f5.6 to match the camera, so the subject is at the correct exposure, but not the ambient fall-off since the flash will only light a part of the scene, making the subject stand out.

If he was to meter the flash at f4, which is the original ‘correct’ exposure for the overall scene, you would end up with, in theory, the exact same light as the ambient, therefore the image would almost be identical as shot without flash, -1 stop.

Remember, f4 lets more light in then f5.6, and flash works with aperture, so by saying the flash needs to be set to have an f4 rating is telling the flash that there is already enough light to only need f4 where in fact you need that extra stop of light to match f5.6

You forget the actual *camera* setting is aperture of f5.6, so the flash will not then put out enough power to compensate the difference between f4 and f5.6. Ergo, flash metering needs to read f5.6 [more light] to match camera’s f-stop, so that ‘more’ light then correctly exposes the subject.

Flash is only light, and if you just pretend for a moment that it’s ‘ambient’ if that flash is then used like ‘ambient’ and you only meter it for f4, with the camera at f5.6 it will simply be underexposed, no different if there had been no flash in the first place.

Hope this explains it.

Trev.

Comment by Trev — January 27, 2012 @ 7:11 pm
Trev,

That was exactly the explanation I needed – totally makes sense (so much so that i can’t believe I didn’t realize it in the first place). Thank you very much for taking the time to post that.

Dave

Comment by Dave — January 28, 2012 @ 11:57 am
Glad to help, as Neil says, sometimes we all have that “aahaa moment” and it clicks into place.

Trev.

Comment by Trev — January 28, 2012 @ 7:30 pm