light meter

I am relatively new to photography (3 years) and very new to using a hand held light meter. I bought this meter (SEKONIC L358) hoping that it would help in my portraiture work using strobes. It does appear to do this ok - saves time in setting up and takes some of the guess work out of the process. However, I am really confused when using this meter in ambience mode - in daylight outside my house. All my images appear grossly underexposed by 1.5 - 2 stops. However inside the house - in abient light they appear to be properly exposed. I know that I can, and do, use my camera's ( canon 40D) suggested reflective meter setting in this case but surely my incident meter should get this at least in the right ball park?

I have gone through the manual for this meter and have experimented exhaustively with this matter - the ISO, mode, and all other settings are correct and duplicated in my camera - which is set in manual mode. The scene is not back lit and I don't think my cameras metering is being fooled.

It is not the meter as I returned the first meter thinking it was faulty - only to discover the same problem. I have another "hybrid" camera which can be set to manual mode and the same problem with underexposure seems to occur....

My question is what's happening? I really cannot fathom this one out?

thanks

Hi, Glenn,

glennmoss said:

I am relatively new to photography (3 years) and very new to using a hand held light meter. I bought this meter (SEKONIC L358) hoping that it would help in my portraiture work using strobes. It does appear to do this ok - saves time in setting up and takes some of the guess work out of the process. However, I am really confused when using this meter in ambience mode - in daylight outside my house. All my images appear grossly underexposed by 1.5 - 2 stops.

Click to expand...

Well. lets check some basics.

First, I assume you have the meter properly configured for ambient mode. (I'm not familiar with that particular meter, so I can''t be more specific than that.) Typically it includes putting into effect an "acceptor" - a flat or dome-shaped diffusing surface over the meter sensor.

Secondly, be sure you place the meter so the "acceptor" is at the location of the subject and parallel to the most important surface of the subject (typically than means flat on to the camera location.) You will see helpful hints about making it face the (principal) light source; that is a bum steer.

Of course, I assume that you set the exposure index setting of the meter ("ISO") to match the ISO sensitivity you have chosen you use in the camera. And then, after metering, I assume you put the camera into M mode and set the f/number and shutter speed to those "suggested" by the exposure meter.

However inside the house - in abient light they appear to be properly exposed. I know that I can, and do, use my camera's ( canon 40D) suggested reflective meter setting in this case but surely my incident meter should get this at least in the right ball park?

Click to expand...

Well, perhaps the incident metering setup you use inside the house is OK (or happens to work OK) but not the one outdoors.

Let me know if you're comfortable with the two guidelines I mentioned above and then we'll go from there.

Thanks, Doug - yes, all callibrated correctly as I said in my OP.

Hi, Glen,

glennmoss said:

Thanks, Doug - yes, all callibrated correctly as I said in my OP.

Click to expand...

Good.

Just what makes you consider your outdoor shot results underexposed? For example, are there objects in the scene that have very high reflectance but which end up in the final image with RGB values that are very modest?

Best regards,

Doug

glennmoss said:

I have gone through the manual for this meter and have experimented exhaustively with this matter - the ISO, mode, and all other settings are correct and duplicated in my camera - which is set in manual mode. The scene is not back lit and I don't think my cameras metering is being fooled.

Click to expand...

Hi Glenn,

Are you sure you have set up the Lumisphere in accordance with the instructions? Incident light readings require the Lumisphere to be fully extended.

From the Sekonic Website said:

Incident readings of three-dimensional subjects are taken using the Lumisphere fully extended, and retract the Lumisphere for selective, narrower-field readings for flat-field objects such as artwork. For reflected readings, a Lumigrid (included) replaces the Lumisphere.

Click to expand...

In addition, are you using the meter at the subject, pointing towards the camera?

Cheers,
Bart

Hi, Bart,

Bart_van_der_Wolf said:

Are you sure you have set up the Lumisphere in accordance with the instructions? Incident light readings require the Lumisphere to be fully extended.

Click to expand...

Well, he said he did everything right, "as he said in his original post."

Best regards,

Doug

Hi, again as above, I believe that I have covered all angles including the lumesphere angles and placement etc. I will take a couple of pictures today and try to post them (not quite familiar with this yet as i am very new here) to show what i believe to be a problem and see what you think.
Thanks

Doug_Kerr said:

Well, he said he did everything right, "as he said in his original post."

Click to expand...

Hi Doug,

I know Glenn did ;-), but in my experience it never hurts to double check the obvious, because what is obvious to one may not be obvious to another. Especially as exchanging the meters gave the same results, user error becomes more likely (especially for someone not yet used to the device).

In my experience with a different model Sekonic lightmeter, one needs to adjust the 'Lumisphere' in one of two positions, and they give different readings. One position is with a receded Lumisphere, but that is basically used to simulate a flat receptor, as in a Lux meter, and is used to set up lights (lighting contrast) and measure for exposures of flat surfaces (where one still needs to correct for direct reflection of glossy sufaces). However, wth the extended Lumisphere setting, one has an incident light meter that handles angles of light like 3D subjects do, shading and all (when used at the subject, pointing towards the camera). The difference between the two methods can give upto something like 1.5 stops difference in suggested exposure.

And then there is also a reflected light metering mode, which gives different results allthogether. And there are potential issues when manually transferring those readings to the camera.

Reading light with a handheld meter is only the beginning of setting an exposure on the camera, because the reading has to be interpreted correctly.

It also doesn't hurt to 'calibrate' the meter to one's camera. A reflected metering from the camera position of a uniformly lit surface should produce a histogram with a spike, approx. centered between the edges. An incident light metering will only give the same result for a surface of appox. 12.5% reflection (which is what my Sekonic is factory calibrated for). Of course one can 'calibrate' the meter for a different response, e.g. by setting the ISO on the meter different to the camera's ISO setting.

Cheers,
Bart

Hi, Bart,

Bart_van_der_Wolf said:

I know Glenn did, but in my experience it never hurts to double check the obvious, because what is obvious to one may not be obvious to another.

Click to expand...

Absolutely, and I was being sarcastic with my observation!

In my experience with a different model Sekonic lightmeter, one needs to adjust the 'Lumisphere' in one of two positions, and they give different readings. One position is with a receded Lumisphere, but that is basically used to simulate a flat receptor, as in a Lux meter, and is used to set up lights (lighting contrast) and measure for exposures of flat surfaces (where one still needs to correct for direct reflection of glossy sufaces).

However, wth the extended Lumisphere setting, one has an incident light meter that handles angles of light like 3D subjects do, shading and all (when used at the subject, pointing towards the camera). The difference between the two methods can give up to something like 1.5 stops difference in suggested exposure.

Click to expand...

I hadn't been familiar with those two configurations. I'm trying (as you might imagine) to relate them to different theoretical outlooks (you know, those pesky cosines!).

Your comment about glossy surfaces is, I'm sure, one of the keys - the way we deal with "non-Lambertian" surfaces.

It also doesn't hurt to 'calibrate' the meter to one's camera. A reflected metering from the camera position of a uniformly lit surface should produce a histogram with a spike, approx. centered between the edges. An incident light metering will only give the same result for a surface of appox. 12.5% reflection (which is what my Sekonic is factory calibrated for). Of course one can 'calibrate' the meter for a different response, e.g. by setting the ISO on the meter different to the camera's ISO setting.

Click to expand...

And indeed the relationships you mention vary with two parameters of the camera's automatic exposure control system:

• What we can think of as the "calibration" of the exposure metering system itself.

• How the manufacturer assesses the ISO sensitivity of the sensor system.

The ISO standard for (free-standing) exposure meters gives a wide range of "calibration factors" that are considered acceptable. The standard for integrated automatic exposure systems does not (there is of course a tolerance expressed, but not a range of "acceptable nominal values").

If we take the calibration specified by the latter standard, and convert it to be applicable to a free-standing exposure meter (reflected-light mode), and postulate:

• A free-standing exposure meter calibrated to that norm (which is typical for serious professional exposure meters), and

• A camera in which the ISO sensitivities are assessed in accordance with the original prescription of the applicable ISO "sensitivity" standard for digital cameras (the "ISO speed" measure)

then we can theoretically expect an exposure, guided by the exposure meter setting (reflected light mode), of a uniform-luminance scene (I choose that just to minimize any complication in what is meant), to give an image with RGB coordinates that represent a relative luminance of about 12.8% of the "saturation" value.

On the other hand, if the ISO sensitivity of the camera is assessed in accordance with the new alternate measure of sensitivity defined by the current applicable ISO standard (the "ISO SOS" measure - Standard Output Sensitivity), then we can expect the exposure described above to give an image with RGB coordinates that represent about 18% of the "saturation" photometric exposure.

Modern Canon EOS cameras evidently have ISO sensitivity ratings assessed in term of the "SOS" measure (and are thus, numerically, about 70% of the value that would be assessed under the original "ISO speed" measure).

An interesting corollary is that on my EOS 40D, midscale on the in-camera histogram corresponds very nearly (for a "neutral" object) to RGB values representing a photometric exposure of 18% of saturation luminance.

To finish the Canon story, Canon these days, although evidently using the "SOS" premise to determine their ISO "sensitivity" values, chooses to express them in terms of a second "new" alternative measure, the "ISO REI" (Recommended Exposure Index). Its definition is this (I have paraphrased to most clearly express the concept):


Of course, the advantage of expressing the sensitivities in that fashion is that nobody can make measurements of actual cameras and then challenge the "truthfulness" of Canon's published "ISO" numbers.

Thanks so much for your input into this.

Best regards,

Doug

test please ignore

My tests

Hi, again. As per my previous posts these pictures were taken outside both with my own camera's suggested reflectance metering and also with my Sekonic's suggested metering - there being [what I consider] about a stop underexposure via my Sekonic. What do you think?


http://www.flickr.com/photos/33123614@N03/4240442640/



http://www.flickr.com/photos/33123614@N03/4240440706/

thanks

glennmoss said:

Hi, again. As per my previous posts these pictures were taken outside both with my own camera's suggested reflectance metering and also with my Sekonic's suggested metering - there being [what I consider] about a stop underexposure via my Sekonic. What do you think?

Click to expand...

Hi Glenn,

It is impossible to say with certainty, because we don't know what the incident light measurement saw, but your incident metered shot is indeed dark. I assume that you had a bright (brighter than average) background/sky behind the camera, in which case the incident meter reduced the exposure suggestion. I also assume your camera used evaluative metering, instead of average metering, which changes the camera measured exposure according to the built-in metering heuristics. The subject is darker than average, I would estimate.

I think most of the difference comes from a misunderstanding about incident metering. Incident metering is only a starting-point! You, the photographer, then needs to decide where on the tonescale you want to place certain scene brightnesses. All the incident meter does is give an exposure where an average scene luminance of 12.5% or 18% (depending on the calibration) will be positioned halfway the output brightness scale. If the scene is darker the output will be darker, and if lighter the final scene will look lighter. Only the light is measured.

The final image brightness will be determined by the amount of light falling on the scene, and the scene reflectance. An incident meter measures the light component, a reflectance meter measures the tones in the scene. They both only tell half the story. And then there is the creative component of where you want the tones to land on the tonescale.

To see if the meter is calibrated correctly, you need to take a reflection metering of a uniform surface, and also shoot the same surface with camera metering. Both should approximately give the same settings, and produce a spike almost halfway in the histogram. On an overcast day that would also result in a similar incident metering result when metered from the subject to the camera.

Cheers,
Bart

P.S. Did you set your camera to M mode to use the incident metering values for aperture and shutterspeed? And make sure there is no EV correction dialed in in M mode, and none in camera metering mode.

Thanks for a comprehensive reply. Yes my camera was in M mode but I'm not sure I understand what you mean by EV correction dialled in M mode. Do you mean pushing the pointer past the centre marking?

I will also try what you said with metering a neutral scene with both camera and meter and see what happens.
Thanks again
Glenn

Hi, again. Just did what you said. I metered a neutral grey card - in reflective mode with my Sekonic - using its adapter and also with my camera's reflective meter. Both are spot on with exactly the same reading.
Glenn

glennmoss said:

Hi, again. Just did what you said. I metered a neutral grey card - in reflective mode with my Sekonic - using its adapter and also with my camera's reflective meter. Both are spot on with exactly the same reading.
Glenn

Click to expand...

Hi Glenn,

Okay, that helps to narrow things down. The Sekonic apparently responds in the same way as your camera's built-in meter for reflective measurements. The camera does have several modes to choose from, so that could lead to differences for specific scene content. The Sekonic response would probably be closest to an averaging approach in the camera. When using a uniformly lit surface those subleties are eliminated, that's why it's a good test.

Basically, all that happens in the Sekonic when you switch to incident metering, is that the meter switches to a different lightpath internally, and that it corrects for the loss of transmission of the Lumisphere. So there should be no difference in the response between reflected and incident metering, presuming that the conditions are uniform (e.g. overcast day, with similar surroundings around the camera).

Since you have a gray card, and assuming it is of good quality and clean, you now can check how the reflected metering of the card surface (with the Sekonic) relates to the incident metering from the card when pointing the meter in the opposite direction (from card to camera, raised Lumisphere). Do note that a gray card reading usually requires to somewhat be angled between the camera and the main light source for a correct reading (to deal with semi-specular reflections). Read the instructions that came with the specific card.

If the gray card has a similar average reflection (usually appox. 18%) as the calibration setting of the Sekonic, then both readings should also be very close. If there is a significant difference, then something seems wrong (maybe it is just that the card has a different reflection). By doing the reflected and incident meterings with the same instrument, we can eliminate a few variables.

I'm curious how that turns out.

Cheers,
Bart

glennmoss said:

Thanks for a comprehensive reply. Yes my camera was in M mode but I'm not sure I understand what you mean by EV correction dialled in M mode. Do you mean pushing the pointer past the centre marking?

Click to expand...

Yes, I'm not sure what possibilities other cameras offer in M mode. My camera doesn't offer the possibility to override the M mode, but perhaps others do. I'm just trying to eliminate possible causes for error in the test.

Cheers,
Bart

There is about a 1 stop difference between the two readings if I have done it correctly. The reflective reading being underexposed relative to the incident in the same meter.
But the incident being similar to my camera's reflective reading with the card.
glenn

Hi, Glenn,

glennmoss said:

Hi, again. Just did what you said. I metered a neutral grey card - in reflective mode with my Sekonic - using its adapter and also with my camera's reflective meter. Both are spot on with exactly the same reading.

Click to expand...

I'm not familiar with the meter involved. What is its "adapter"? (you may have mentioned that earlier in the thread, and if so forgive me - I have just skimmed the thread!

Just for reference against my theoretical observations earlier, that suggests that the "calibration" of the Sekonic and the "metering" part of the camera's automatic exposure control system are consistent.

Incidentally, in the case of Canon EOS cameras, and assuming an "appropriate" calibration of an external expsure meter, we generally find that consistency.

But there is also the matter of the assessment of ISO sensitivity used in the camera.

On a test shot of the neutral card based on either the Sekonic meter (in reflected light mode) or the camera's metering system, what RGB values do you get in the image for the neutral card?

Regarding comparisons between incident and reflected light measurements (with the same meter, for example).

Note that the meter "calibration factor" is separate for the two modes, as the physical quantity being measured is different (luminance in the case of the reflected measurement, illuminance in the case of the incident measurement).

If the manufacturer, for example, chose to set up the meter so it followed, for each mode, the midpoint of the range of calibration factors "allowed" for that mode by the ISO standard, then in theory a consistent exposure would achieved for a scene whose average reflectance was about 16%. That is not to suggest that meter manufacturers do that.

Because of the obsession with the idea of an average scene reflectance of 18%, we might expect meter manufacturers to use calibration factors that made the exposures based on measurements in the two modes consistent for an average scene reflectance of 18%.

In any case, the exposure given by a reflected light measurement and an incident light measurement (say, with the same meter) will vary with the average reflectance of the scene.

The lower the average reflectance of the scene, the greater will be the exposure called for by the reflected light measurement compared to the exposure called for by the incident light measurement.

Best regards,

Doug

R 116
G 115
B 110

Via camera's metering system viewed in cs4 via "info"
The adepter replaces the lumisphere - used when taking a reflective reding
cheers
glenn

Hi, Glenn,

glennmoss said:

Hi, again. As per my previous posts these pictures were taken outside both with my own camera's suggested reflectance metering and also with my Sekonic's suggested metering - there being [what I consider] about a stop underexposure via my Sekonic. What do you think?

Click to expand...

Just to be sure I know what is what, is:

• The first shot taken based on the (reflected) metering by the camera, and

• The second shot taken with exposure based on an incident light measurement with the Sekonic ?

If so, the comparison of exposure results would tell us that the average reflectance of the scene is lower than the value that would produce corresponding exposure results in both cases (which value might well be 18%, but we can't be certain). It does not bespeak any inconsistency between the two metering instruments.

We can only expect consistent results between reflected light and incident light measurements (even between two consistent instruments) except for a certain value of average scene reflectance.

Stated a different way:

• Exposure governed by reflected light measurement puts the average photometric exposure over the part of the scene regarded by the meter at a predetermined fraction of saturation


• Exposure governed by incident light measurement puts the photometric exposure for a scene item of any specific reflectance at a predetermined fraction of saturation.


This metaphor illustrates the attraction (for some work) of incident light metering.

I like your "model". Here we have, for the same purposes, "Stella", formerly employed in the hat department of a department store. I think your model is cuter.

Thanks.

Best regards,

Doug

Thanks for all your replies and I [think] I know what you mean, Doug. The average reflectance of "this" scene "is lower than the value that would produce corresponding exposure results in both cases". Yes that makes sense.

I will continue to experiment with this so that i can get it clear in my own head - and i may learn a thing or two on the way.

cheers
Glenn

glennmoss said:

There is about a 1 stop difference between the two readings if I have done it correctly. The reflective reading being underexposed relative to the incident in the same meter.
But the incident being similar to my camera's reflective reading with the card.
glenn

Click to expand...

Okay, that seems to suggest that your gray card might be a bit brighter than 18% or its surface a bit shiny, but that the incident meter, giving the same result, and your camera more or less agree.

What follows it that the scene reflectance in the scene with your model was a fair bit darker than average (18%), and your camera therefore increased the exposure to compensate. The incident metering of the model however was uninformed (afterall, how could it?) about the darker than average scene. However, in the latter incident metering case, the photographer has the freedom to adjust the exposure parameters based on his/her judgement, and that is typical for incident metering.

I do feel that the incident metered shot of your model was quite dark, but there may have been reasons for that (e.g. a small source or a reflection of light falling on the meter), only you can reconstruct that.

Cheers,
Bart

Hi, Glenn,

glennmoss said:

I will continue to experiment with this so that i can get it clear in my own head - and i may learn a thing or two on the way.

Click to expand...

It sounds to me as if your thinking on this is well organized, and I am optimistic that you will be able to figure out what is happening!

There are many complications here, and neither pragmatic not theoretical considerations alone will allow us to figure out the real story!

Both Bart and I tend to do this "triangulation" from different vantage points, but the result is usually a tasty stew!

Best regards,

Doug

Bart, you mentioned that the incident reading was only half the story..I would be interested to know
the other half.

Glen, if your camera has a spot meter, could you take a reading off the face of the model and let us know
how much it differs from the incident reading.
Also, I presume the model face approximates a white caucasian skin ( folks..this is just for exposure
measurements and ev comps. no other meaning is either implied nor must be read into it. my face
requires a different ev comp than my wife's does! and thats why we are never photographed together!)

Bart/Doug..are you saying that just transferring the incident meter readings to the camera will
give the correct results?

Thank you.

fahim mohammed said:

Bart, you mentioned that the incident reading was only half the story..I would be interested to know
the other half.

Click to expand...

Hi Fahim,

An incident reading (pointing from subject to camera) of a uniformly lit scene will place an average scene reflection (say 18%) almost halfway on the histogram. Let's assume the scene is low contrast. That would mean that the exposure of bright subjects is not going to reach the right side of the histogram (whites will be light gray) and the exposure of dark subjects will almost not reach the the left side of the histogram (blacks will be dark gray). If e.g. our intent is to have a bright looking scene with clean whites, then we may need to adjust the incident reading/suggestion with a +1EV or more. We could do that in postprocessing but underexposing by 1 or more stops will increase noise and reduces Dynamic range.

On a high contrast scene, say no clouds and a direct sunshine from one side, the incident reading still places an average scene reflection halfway the histogram, but both highlights and shadows may be clipped. In that case the photographer needs to choose to either retain highlight info by adjusting the incident reading/suggestion downwards (and e.g. use fill flash or a reflector to save nearby shadows), or choose to keep the shadow detail and let the highlights clip/blow out (or shade the highlights or use a diffuser to soften the lightsource).

The actively thinking photographer is still needed with an incident meter.

Bart/Doug..are you saying that just transferring the incident meter readings to the camera will give the correct results?

Click to expand...

For average scenes it will create an average exposure. Whether that's a correct exposure depends on what we want to achieve.

In studio lighting scenarios we have a lot more control over lighting contrast. For recognisable product photos we may want to reduce the lighting contrast to 2:1, which when combined with a subject contrast (e.g. 100:1) will produce a total contrast of 200 to 300:1 (depends on the placement of the lights), which will already be a challenge to print, so we may want to reduce the lighting contrast even further, at which point we could use a simple incident reading directly as camera setting, unless one uses slide film. Slide film shouldn't be overexposed, so the exposure depends on the amount of white in the subject. If there is no white in the subject, we are offered a choice to increase exposure or keep it as it is.

Those are just a few examples of how one can use the guidelines of incident metering.

Relective metering is in fact easier if we can spot measure small areas, because we can sample highlights and shadows and determine the limits and the contrast directly, and fit them within the dynamic range of our recording material. Measure something white and on a digital camera add 3 stops of exposure to get very close to clipping white, or a bit less to keep it a bit darker if the shadows allow. Slide film has less latitude, most negative film has a bit more.

Cheers,
Bart

Hi, Fahim,

fahim mohammed said:

Bart/Doug..are you saying that just transferring the incident meter readings to the camera will
give the correct results?

Click to expand...

Assuming that the meter calibration and the camera's outlook on ISO sensitivities are "appropriate", then shooting at the camera exposure indicated by an incident light meter will result in high reflectance items in the scene having a "high" exposure result (high RGB values) and low reflectance items in the having a "low" exposure result (low RGB values), regardless of what the range of reflectance is or what the average reflectance of the scene is.

For example, if includes only a white handkerchief on the side of a giant coal pile, in the delivered image the handkerchief will have very high RGB values, and the rest of the scene (coal) will have very low RGB values.

If we then place the same handkerchief on a pile of crushed white stone, use the incident meter again (in case the lighting is different in that part of the site), and shoot as indicated by the meter, the RGB values of the handkerchief will be the same as in the first shot.

Now whether those RGB values for the handkerchief are what you would want to see is another matter altogether, because:

• The meter may not be calibrated the way we think (remember, the standard for that allows a range of calibration factors)

• The camera may not reckon ISO sensitivity the same as was contemplated by the "wizards" who developed the exposure meter and ISO sensitivity standards.

• Your view of "how far to the right" in the exposure result scale a white handkerchief should show up may differ from the view held by the wizards.

But it's a more predictable result, in the terms I described, than we can get with reflected light measurement.

Best regards,

Doug

My Canon 40D is evidently a "point and shoot" camera. I find that if I don't point, I won't get a picture of what I want, and if I don't shoot, I get no picture at all.

Bart, Doug...

I do appreciate you two taking the time to give me of your experience re: incident light meters.
Do I understand it...honestly I have to say maybe yes, maybe no, maybe sometimes when it is
explained as well as you two have done in this thread.

However, I shall stick to my kludge..meter and let experience guide me for ev compensation.
Not really scientific, but works pretty well for me. Or else carry my spot meter with me and
place tones in the zones I would like them to fall. Again not very accurate as I let the lab do the developing. Do not do wet prints either..so there go two elements of control for properly deriving benefits of handheld light meter readings. I am talking about b&w film of course.

Thanks and regards.

fahim mohammed said:

However, I shall stick to my kludge..meter and let experience guide me for ev compensation.

Click to expand...

Hi Fahim,

Nothing wrong with "sunny 16" either, it's just that metering can give that (slight) improvement, especially when the lighting conditions are more complex, or when we don't have enough time to consider the consequences. Of course with digital, it's easy enought to bracket when indoubt, or shoot while following the histogram untill we've got it.

Cheers,
Bart