Light meter technique

Hi all,

 

I have a question concerning the use of a flash meter to determine

lighting ratios.

 

Currently, I use the flash meter by positioning it at the subjet and

pointing it at the camera. I do this for both the lit and filled

areas of the subject, and adjust the power/position of the lights so

as to give me the desired f-stop value for the main light and the

desired ratio between the hightlight and shadowed areas. When using

the flash meter I flash ALL the lights, so that they are all taken

into account.

 

I've just read about another technique which involves the following:

 

Place the light meter at the subject position.

For each light, flash ONLY that light with the meter facing the

light, so as to get its incident reading.

Adjust the power of the lights to get the ratios desired.

Place the meter at the front of the suject and flash all the lights

to get the overall exposure setting for the camera.

 

 

When calculating the ratios like this you must take into account the

overlap of the flashes. For example, assuming that you want a 2:1

ratio, with a key light to the left of a subject and a fill light at

the camera position, the fill light will light both side of a face

evenly, whereas the key light will only light the left. With both

flashes at the same power, the left will therefore be 2 times brigher

than the right (since both flashes are lighting it). When checking

your rations, you need to consider this in advance and ensure that

both incidence readings give the SAME reading.

 

The second method seems more complicated to me. However, there are

people who use it, so I assume that it must offer some advantages.

 

So, my question is, what are the advantages of each method?

 

Thanks,

 

Tim

The second method is more accurate for multiple lights. The power settings are not accurate enough for that purpose. The light reflected from the subject depends on the distance, modifiers and angle of the lights. If you want to nail the lighting, you have to measure it.

Hi,

 

I'm sorry, can you explain what you mean in more detail.

 

I don't understand why measuring one light at a time would be more accurate than reading all the lights, thereby assuring that you mesure what actually falls on an object.

 

There seems to me to be lots of room for error in the second method.

 

Thanks,

 

Tim

First, it's correct that an exposure measurement must be made using the incident hemisphere with all lights flashing. What is arguable is whether that measurement should be made with the hemisphere facing the main light or the camera. Certainly there are photographers achieving excellent results either way, but there is a reason to prefer one or the other. This is shown by a bit of history.

 

There are two major branches of film: Transparency and negative. Transparency inherently has greater ability to maintain detail in shadows with underexposure, but is vulnerable to losing detail in highlights with overexposure. Therefore, photographers shooting negative film have learned to "expose for the highlights"--expose with a bias in metering technique toward ensuring important highlight details remain, and let shadows more or less fend for themselves.

 

Negative film inherently has greater ability to maintain highlight detail with overexposure, but is vulnerable to losing detail in shadows with underexposure. Therefore, photograpers shooting negative film have learned to "expose for the shadows"--expose with a bias in metering technique toward ensuring important shadows retain detail, and let highlights more or less fend for themselves.

 

Thus, a transparency film photographer will tend to point an incident meter toward the main light to get the all-important highlight measurement. With the hemisphere, the "impact" of other light sources will be factored in, but the important thing is to ensure that the highlights are exposed safely within the film's range.

 

On the other hand, the negative film photographer will tend to point the incident meter toward the camera (actually, toward the fill light) to get the all-important shadow measurment. Using the hemisphere, the main light is factored in, but the exposure is based primarily on the fill light, making sure the shadows are captured within the film's range.

 

In either case, experience with the film's dynamic rnage may guide the photographer in how to "tweak" the reading further, especially when the photographer who predominantly shoots negatives uses the "negative technique" for his transparencies or the transparency shooter uses the "transparency technique" to shoot negatives.

 

Inasumch as most portraits have been shot with negative films, the great majority of portrait photographers learned and teach the negative technique...indeed, they may not even realize the transparency technique exists or understand why it works.

An interesting question and as the above poster says, the answer depends on whether using slide/digital vs negative stock. The best way to learn is to do. So meter both ways, write down the answers, make a sketch of your set up and shoot from two stops more open, to one stop above eg reading f8 so shoot f4 to f11 at half stop intervals. I did it recently with a negative film and was amazed at how much more light I needed than my flash meter said. In fact, metering by pointing the meter towards the reflector, not the key light, was just about right!

'The second method seems more complicated to me.'.............................................

 

'There seems to me to be lots of room for error in the second method.'........................................I would suggest to you that the opposite is true, that the second method is a very accurate way of measuring the output of your lights and setting up light ratios. You turn on a light, adjust the power up or down, point your incident meter straight at the light(many incident meters will have a translucent dome, but a flat translucent disc is far more accurate for these types of measurements[pointing/measuring a single light source in incident mode]),..................and you simply measure the light that's hitting your meter, you're measuring output, WITHOUT considering any angles, ratios, or modeling, NOTHING ELSE, JUST the output of the light.

 

This I suggest is the best method to use to gauge what a light is putting out at any particular power setting, that is pointing the light STRAIGHT at the lightsource and measuring its output in f-stops,............ of course it follows that you need to have an accurate way of measuring your lights INDIVIDUALLY, before you measure them together, particularly if you want to figure light ratios between different light sources. Pointing the meter straight at a light source is the key to getting an accurate reading from an individual lightsource, holding the meter at an off angle to the lightsource will introduce a shadow which the meter will incorporate into a reading which will give you a reading for the lightsource AND the shadow, and NOT the lightsource alone(which is why the flat translucent disc is even more accurate when using this technique).

 

There's nothing complicated about this, it's not rocket science, it's just a common sense approach to checking out what a lights putting out, turn a light on, adjust the power to where you think you want it, and measure pointing the meter straight at the light to see if the lights creating the illumination via f-stops that you either want or don't want.

 

The concept of light ratios and the idea of key/fill lighting is harder to explain than it is to understand, but the main point where many folks seem to get tripped up, is in understanding that when using multiple lighting, you'll many times have two or more lights HITTING THE SAME SPOT,..........and in a case where you have more than one light hitting the same spot, it's total illumination of all the light hitting a spot that you want to measure simply because that's the light that hitting that spot, plain and simple, if you're not measuring all the light hitting a particular spot, you haven't made an accurate measurement.

 

You'll often have more than one light illuminating the same spot when you use two lights together, one as a "key" light, and one as a "fill",....the key light, which is typically the more directional lightsource, establishes the mood of the scene, it simulates sunlight coming through a window or whatever you're trying to establish.

 

When using a light as your 'key', and particularly if it's a directional lightsource, it'll create TWO SPOTS on something, it'll create BOTH the illumination on something, and a shadow. Exposing for the illuminated part, may leave the shadow black where you see absolutely no detail, so adding a non-directional lightsource to illuminate the shadows created by your 'key' light, will give you detail in those shadows, and since it's non-directional, it won't create any shadows of its own, so what you've done is used two lights to create the 'illusion' of one light illuminating your scene with detail you can see in the shadows. You've used two lights to make it look like you've used one that shows detail in the shadow areas.

 

A directional lightsource used on a 'head n shoulders' portrait is going to create highlights and shadows on the face, a non-directional/very soft illumination from a second light, used as a fill, is going to tend to go everywhere, so that pointing this second light at this very same face, will ALSO ILLUMINATE the area where the 'keylight' is creating a highlight on the face, and in the shadow areas left by the keylight.

 

Said another way, there will be parts of the face in the above scene where your two lights will be hitting the same spot, you need to measure that total when exposing for that area because that's the amount hitting that spot, simple as that, and that light(the total from two lights) is going to register on your film regardless of what you do, because IT'S THERE.

 

The relationship of the illumination between your highlights and you r shadow areas in a scene, is what you're figuring as a light ratio, and in the above example, it's the total illumination from two lights(key and fill), creating the highlights on the face, versus the illumination of the shadows by the 'fill' light only.

 

If you're using a key and fill light together, the ratio is key + fill to fill, with the proviso that one light is more directional, which tends to create shadows, and that the other is more of a non-directional light which doesn't create shadows. This is a key point, because if both lights are creating shadows, it won't look natural, it won't look like one light is illuminating the scene where you can see detail in the shadows, the illusion will be destroyed, and it'll look like what it is, TWO LIGHTS. Said another way, for the 'key' light and 'fill' light(used together) technique to work, you have one creating the shadows, and the other light has to be a softer light which doesn't create shadows. And one typically should be MORE INTENSE that the other,..............the 'key' light should be more intense than the 'fill' light, because if they're the same intensity, they're BOTH going to create shadows, and again the illusion of seeming to use one light(where you've really used two), will be lost.

 

That's the problem with a 2 to 1 light ratio, to get 2 to 1, the key and fill would have to be equal, do the math, if the key and fill are equal, that's 1+1 which equals 2 which is hitting the highlight portions of the face, and 1(from your fill) hitting the shadows, and since the both lights are equal, they won't function as a key and fill to each other because they'll both create shadows. Set this up in the studion to confirm it.

 

If your fill light is 1 stop below your key, you'll have a 3 to 1 light ratio, and you'll have less of a tendency for your fill to create shadows, many folks try to all keep the fill light close to the lens axis as it points at the subject matter to help eliminate any shadows from the the fill light, and this is what I do(placement doesn't have to be exact, just in the general area of the lens axis). So let's say from 2.5 to 1 and from there, addresses the 'double shadow' issue, which is important because when doing a portrait, you don't want two sets of shadows from two lights coming from the sitters nose, although I'm sure somebody somewhere will insist on doing it just this way as an artistic choice, bottom line, two sets of nose shadows looks like shit to me.

 

The second technique you descibed is exactly how I meter, measure the lights individually, check their illumination individually, point the meter straight at each light as I go, figure out how intense I want the lights in realtion to each other, and then I turn everything on, and measure the illumination of all the lights by pointing the meter at the camera(incident mode w/a tranlucent dome), to get an overall exposure, of course you can make errors doing it this way, but that isn't the point, the point is seeking accuracy with each individual light, which helps your accuracy in calculatiing light ratios, or whatever you want to calculate in using your lights together.

 

www.imageandartifact.bz

 

 

 

 

"Thus, a transparency film photographer will tend to point an incident meter toward the main light to get the all-important highlight measurement.".........................................Kirk, I would say this, for transparency film, I would suggest that it's even more critical to get a total from your key and fill because of how a transparency deals with highlights, as opposed to a technique that would 'bias' toward the key and away from the fill.

 

The key here is what makes up the highlights? In terms of using a key and fill, it's more than one light, and in the case of a fill light being utilized in a 3 to 1 ratio, that's half the illumination coming the main, that's a BIG CHUNK of the illumination hitting the highlight ON TOP of the illumination coming from your main, and in that scenario, to bias away from the fill toward the main, when the fill is creating a substantial portion of the highlight is going to cause overexposure.

 

I also think there are other considerations to address when you bias a meter reading toward one light or the other in a multiple lighting set-up, and between highlight and shadow, namely what hasn't been mentioned, which would be 'old hat' to the zone folks, the idea of exposing for one and developing for the other.

 

Transparecies tend to blow out the highlights with enough overexposure, and when using transparency film, I don't change my metering technique, I simply bracket exposures from my calculated meter reading.

Thanks for your responses.

 

Unfortunately, you haven't managed to answer my question :)

 

I completely understand the technique of measuring each light one at a time and then taking an overall exposure. It's logical, I can see why it works.

 

But why would that be better or more advantageous than measuring the ratios by flashing all the lights and pointing the meter at the camera? In doing this, you're taking into account the total light hitting the brighter side (key + fill) verses the fill only side. Should you decide for whatever reason not to have even fill, then it's taken into account.

 

Thanks,

 

Tim

Oh, I forgot to add something. My thought process is like this:

 

For this subject, fX will give the desired DOF

Set up lighting

Expose brighter side to give desired fstop

 

This works because I'm alreading exposing for the total amount of light hitting the subject (key + fill). If I'm only measuring one light at a time then I can't do this.

 

Tim

If you "flash all the lights and aim the meter at the camera," your measurement cannot account for all possible light sources. What if you want to employ a background light? Or, a hair light?

Your meter will not read 360 degrees. Each light source must be measured and the relative outputs balanced to achieve the effect (ratio) you want.

 

But, suppose you did have a meter that could measure all light from all angles in one exposure. How would you know how to adjust each light source to achieve your desired balance except by constant trial and error? That's possible with a digital camera, but very time-consuming and not very scientific.

 

The most accurate and efficient method is measuring each source separately.

Talk about off-topic responses...

 

Ok, Tim, if you use two identical lights, with identical settings and modifiers and at equal distances, you might as well take a single reading with an incident flash meter, facing the lens. However, that's usually not how you light something.

 

Most often, you will use a broader, softer light for fill, and a somewhat smaller, harder light for the key light. To that, you might add an hair light and background light for better control, possibly a kicker. Each usually has a different kind of reflector or modifier, so the power settings are meaningless.

 

If your setup is consistent, you probably don't have to do the full-monte each time. In any case, you do it before the client arrives - they are not interested in your techie gymnastics. Once you gain some experience, you can probably reproduce several setups without detailed metering, for portraits at least. Product and commercial setups are seldom that simple, so it's back to basics each time.

Thank you. A good point.

 

Effectively I see that in a complicated lighting situation you'd be better off measuring each light at each important point to find out the total eV values for the highlight/shadow area.

 

In the case of a simple set up with one key light and one fill, it's possibly quicker and easier to flash all the lights. However in this case both mothods will work and personal preference takes precidence.

 

Would you agree?

 

Tim

You still take an overall reading, with all flashes, for the final exposure - you can't simply add EV values, and there's no point in doing so.

 

On your second question, I agree. To paraphrase Einstein - do as little as possible - but no less.

'But why would that be better or more advantageous than measuring the ratios by flashing all the lights and pointing the meter at the camera?' ..............................if you understand the ratios, then you should understand this, take a 2 light set-up w/a 3 to 1 ratio key to fill, your key is F5.6, your fill is F4.0, where light sources create the highlights your exposure IS F6.5-6.7(I don't have my meter in front of me, but your total illumination will be half-way from F5.6 to F8), now matter how you point the light meter when both lights are on, this is the illumination hitting the highlights.

 

In the above example, if your lens can see the highlights, pointing an incident meter with a translucent dome straight at the camera from in front of the subject matter to position the dome the same way as the sujbect matter and illuminate the dome in the same way as the light illuminates the sujbect, should give you a reading of F6.5-6.7 but metering with both lights on and pointing the meter at the camera in the above scenario, MAY OR MAY NOT GIVE YOU the F6.5-6.7 WHICH IS THE ILLUMINATION for the highlights whether you metered right or not, YOU KNOW from meter each light sepearately that you've got F5.6 from one, and F4 from the other, your total illumination on the highlight area IS F6.5-6.7, so the point to checking each light separately is piecing together how the illumination from each light makes up the total exposure. I mean if you don't do each light, you can get an overall exposure, but how do you know the relationship between the lights is where you want it?

 

Also you can check your overall exposure taken w/a meter reading with all the lights on, against what you know to be true from the individual readings, again, if one light is putting out F5.6, and another F4.0, their combined illumination is halfway to F8, you meter with all the lights on you'll either get this reading or your won't, the fact that you're aware of what it should be, and that you've either gotten the same reading or something different for whatever reason is the WHOLE POINT. Plus the fact that pointing the meter at the camera IS NOT going to always measure all of the lights when you have multiple lights going(the above mentioned hairlights/kickers).

 

In the above example, you turn off the fill, then the light illuminating the highlights is F5.6, and nothing illuminating the shadows if the key is directional enough, pointing the meter at the lens in this instance, doesn't give you the lights illumination, it gives you a compromise reading between the light and the shadow the light leaves, ........................the point to all of this and using a meter is to know when to mentally swich gears between measuring illumination from a lightsource, and pointing your meter in a direction to measure something else, a light and a shadow, and/or multiple lighting.

 

There's measuring illumination, and something altogether different, which is pointing your meter in a direction to combine the effects of highlight and shadow, and these are 2 things/concepts which combine at points, and separate from each other at points, in terms of how they effect your overall exposure, and this is why I use the second technique.

Hi Jonathon,

 

Thanks for your detailed example. The advantages are now beginning to fall into place in my head. I now see the advantage is the absolute precision that you have over the ratios. The obvious disadvantage is the extra time (flash each light at each location of importance) and mental arithmetic involved.

 

Up till now you suggested using the meter to find the overall exposure once the lights have been set up. I'm still not sure how you go about setting up the power of each light easily if you are ailing for a particular DOF. For example, suppose that you decide that you need f/8, and you want a 3:1.

Can you explain the mental arithmatic you go through to do this please? What values do you metering to to get the desired effect.

 

Thanks again,

 

Tim

If you've got the time, then being as accurate and precise as you can is important in knowing the starting point for each light, and you can re-check between the invididual readings and taking an overall reading with all your lights on, I take this kind of time to fine tune my exposure, on a paid job, or on a special personal project, to check and re-check, catching all my mistakes and miscalculations before the shoot.

 

Being methodical forces you to think about this, after you do it enough, it's like driving, you get a 'feel' for it, and through constant practice, you begin to understand light ratios/flash-fill and the other nuances of lighting, and you'll start knowing what your lighting will look like before you get it back from the lab, when you work out a scheme, and it ends up working out just like you'd though it'd be, for a portrait photographer, it's almost as good as SEX.

 

I gave you an example of a lighting scheme utilizing a 3 to 1 light ratio, with the key @ F5.6, and the fill @4.0, and with the intensity of the fill @ 1 stop below your key, you'll always be at 3 to 1, and the above example gives you an exposure of F6.5-6.7 for the highlights and F4 for the shadows.

 

To increase DOF by going to F8 simply increase the power/illumination on both lights an EQUAL AMOUNT, until you get a reading of F8 with both lights on...........I don't have my meter with me but that increase should be somewhere around F6.5-6.7 for your key, and F5.0 for your fill, this should give you close to F8 for both lights hitting the same spot.

 

You raise and lower the power an equal amount on both lights, you stay at the same ratio, raise/lower one more than the other, you change the ratio,.......................after you do this enough, you can cut out some of the steps, and of course you may start out with this kind of scheme, but come up with some inspiration that totally disregards what we've been talking about, and playing around with all this doesn't mean you're a slave to it, the best exposure ultimately, is the exposure that makes your shot look the best.

 

When I shoot a dark skinned African American like my wife, and I intentionally overexpose via 'high key', I've done it so many times, that I set up my ratio to something like 2.5 to 1, with both key and fill going, I'll raise and lower unitl I get F5.6(both key and fill hitting the same spot), I'll ignore F5.6, and start shooting between F8-11, because I know what's going to happen, which is that 1-2 stops up from what my meter is telling me is when a certain skintone shot 'high key' starts to look right, TO ME, so all this is not supposed to confine or restrict you, but give you a precise idea of what your lights are doing invidually at the starting point, after that, depending on your ideas/inspirations, you adjust to taste.

 

These folks are right on when you do this if you're doing a clients portrait, I do this before the shoot, everything is set up the night before, the morning of the shoot, I fire everything up, make a final check that nothings been moved, changed, and then when the client shows up, I concentrate on making personal contact with the client and brainstorming ideas.

Here's a 'high key' shot of Dayna, I uploaded this a few threads ago, and I'll share it again with you, I believe my key and fill were around 2.5 to 1 or it could've been 3 to 1, and with both lights on, my meter read @ or just above F11, I left my lights at this intensity, and began shooting by setting the lens to F8 and bracketing up toward wide open, this shot's somewhere around F4-5.6, the meter was pissed, but Dayna and I liked the effect.<div></div>