Light Meter reliability in bright sunlight

Thucydides2 said:

I shoot outdoors with bright sunlight on the subject, I get very high readings (i.e. F10 for 1/128th power at ISO 100 and 1/180th shutter speed.)

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The Sunny 16 Rule tells us the correct exposure for your stated condition with ambient light only would be in the neighborhood of f16 @ 1/100 (the reciprocal of the ISO rating), which is equal to f11 @ 200 - not too far from your reading.

Thucydides2 said:

Hi Everyone. This question may have been asked and answered, but I have not been able to find an answer.

I use a Kenko KFM-2100 light meter in non-cord mode for metering flash in my studio setup and do not have any problems - everything makes sense in terms of exposure stops for my speedlights and camera. When I shoot outdoors with bright sunlight on the subject, I get very high readings (i.e. F10 for 1/128th power at ISO 100 and 1/180th shutter speed.) If I move the flash into the shade and measure at the same distance I may get F2.0, which seems more reasonable. Is this a recognized problem with light meters measuring in flash mode in sun? My interest is in shooting flowers, lowering the ambient exposure and "filling in" with flash at the correct exposure. Again, I apologize if this has been addressed before.

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Sounds as if your meter is measuring flash PLUS the ambient light.

For this situation I would put aside the meter and work from the camera review screen and histogram. With a little practice you should be able to set up just as quickly and maybe have a better view of what's happening.

I have not done this kind of thing with a meter since the film days and really don't remember how, but if you want to use the meter maybe someone here can help.

Gato

Thucydides2 said:

Hi Everyone. This question may have been asked and answered, but I have not been able to find an answer.

I use a Kenko KFM-2100 light meter in non-cord mode for metering flash in my studio setup and do not have any problems - everything makes sense in terms of exposure stops for my speedlights and camera. When I shoot outdoors with bright sunlight on the subject, I get very high readings (i.e. F10 for 1/128th power at ISO 100 and 1/180th shutter speed.) If I move the flash into the shade and measure at the same distance I may get F2.0, which seems more reasonable. Is this a recognized problem with light meters measuring in flash mode in sun? My interest is in shooting flowers, lowering the ambient exposure and "filling in" with flash at the correct exposure. Again, I apologize if this has been addressed before.

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IMO your meter is probably performing as expected.

Your meter is reporting the exposure for the ambient plus flash light when you take a flash reading. In bright sunlight you can expect a high reading due to the sunlight alone. Adding some flash will raise the light level even more depending upon how bright and close you flash is to the subject.

Your meter has an "analyze" function to tell you the approximate proportion of flash light in the total exposure. On the KFM-1100 model this is a circle with 4 quadrants that report the % Flash values as 25%, 50%, 75% or 100% of the total exposure. Your KFM-2100 model may be similar or perhaps reports in finer increments.

How much flash you add to the ambient light depends upon the look you want to achieve. With portraits a number of sources suggest limiting flash content for bare fill flash to around 30%. Any higher and it can become rather obvious flash was used requiring you to soften the flash with modifiers. I don't know how this plays out when shooting flowers.

The % Flash value is related to the amount of stops the flash increases the ambient only exposure F value. This post has more information on determining % Flash by observing just how much the flash increases the ambient exposure.

Using fill flash to overpower bright sunlight requires the flash to be quite close which for shooting flowers may not be a serious issue for you. Keeping a focal-plane shutter camera within its flash sync range will restrict you to small apertures. For a more shallow depth of field look the two common techniques are using HSS flash or ND filter on the lens. This is one area where a leaf-shutter camera has an advantage.

• John

--
"[If you don't sweat the details] the magic doesn't work." Brooks, F. P., The Mythical Man-Month, Addison-Wesley, 1975, page 8.

Yes - but i am trying to measure flash output not ambient light. In bright sunlight I am getting a meter reading of F10 in flash mode (at very low power settings.). If I move the same setup (including distance) to shade, I get a flash reading of F2 (for the same power setting.) It seems like the meter is reading both the flash and some ambient light. This is not a problem indoors. Is this to be expected or is it a problem with the light meter?

Thanks, John. I assumed the meter was distinguishing between flash and ambient based on duration and only giving me a flash reading.

I am shooting flowers in very harsh sunlight. One technique I like to employ is to expose for the conditions in camera (1/180 f/8 ISO 100) match the exposure with a speedlight in a reflector with diffuser, and then drop the exposure in camera one to two stops. This results in a highlighted flower with good color saturation - it is an outdoor portrait look. I shoot tethered, and there are certainly multiple workarounds, but I like trying to get as much "in camera" as I can.

I am usually using either a macro or telephoto lens so shallow depth of field (or lack of) isn't an issue.

As far as I can tell from a quick search, your meter has an analyze function that tells you how much of the exposure is ambient and how much is flash.

If your meter didn't come with a manual, it's available on the net.

fotowbert said:

Thucydides2 said:

Hi Everyone. This question may have been asked and answered, but I have not been able to find an answer.

I use a Kenko KFM-2100 light meter in non-cord mode for metering flash in my studio setup and do not have any problems - everything makes sense in terms of exposure stops for my speedlights and camera. When I shoot outdoors with bright sunlight on the subject, I get very high readings (i.e. F10 for 1/128th power at ISO 100 and 1/180th shutter speed.) If I move the flash into the shade and measure at the same distance I may get F2.0, which seems more reasonable. Is this a recognized problem with light meters measuring in flash mode in sun? My interest is in shooting flowers, lowering the ambient exposure and "filling in" with flash at the correct exposure. Again, I apologize if this has been addressed before.

Click to expand...

IMO your meter is probably performing as expected.

Your meter is reporting the exposure for the ambient plus flash light when you take a flash reading. In bright sunlight you can expect a high reading due to the sunlight alone. Adding some flash will raise the light level even more depending upon how bright and close you flash is to the subject.

Your meter has an "analyze" function to tell you the approximate proportion of flash light in the total exposure. On the KFM-1100 model this is a circle with 4 quadrants that report the % Flash values as 25%, 50%, 75% or 100% of the total exposure. Your KFM-2100 model may be similar or perhaps reports in finer increments.

How much flash you add to the ambient light depends upon the look you want to achieve. With portraits a number of sources suggest limiting flash content for bare fill flash to around 30%. Any higher and it can become rather obvious flash was used requiring you to soften the flash with modifiers. I don't know how this plays out when shooting flowers.

The % Flash value is related to the amount of stops the flash increases the ambient only exposure F value. This post has more information on determining % Flash by observing just how much the flash increases the ambient exposure.

Using fill flash to overpower bright sunlight requires the flash to be quite close which for shooting flowers may not be a serious issue for you. Keeping a focal-plane shutter camera within its flash sync range will restrict you to small apertures. For a more shallow depth of field look the two common techniques are using HSS flash or ND filter on the lens. This is one area where a leaf-shutter camera has an advantage.

• John

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A tidbit to add to this good explanation is that the flash meter does have a (usually) fixed metering duration of probably around 1/100 second, and it distinguishes the sudden increase of light caused by the flash within that duration.

Thucydides2 said:

Thanks, John. I assumed the meter was distinguishing between flash and ambient based on duration and only giving me a flash reading.

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I'm not aware of any flash meters like that. The ones I have seen all report total exposure when ambient light is present during a flash reading. Understanding the relative mix of flash and ambient light requires either the use of % Flash (for meters that report % Flash) or by taking reading with and without flash as I reported here .

Thucydides2 said:

I am shooting flowers in very harsh sunlight. One technique I like to employ is to expose for the conditions in camera (1/180 f/8 ISO 100) match the exposure with a speedlight in a reflector with diffuser, and then drop the exposure in camera one to two stops. This results in a highlighted flower with good color saturation - it is an outdoor portrait look. I shoot tethered, and there are certainly multiple workarounds, but I like trying to get as much "in camera" as I can.

Click to expand...

When your flash exposure matches the ambient exposure that is a 50 % Flash situation. The total light is doubled and the aperture is closed one stop to compensate. The analyze function of your meter would be expected to indicate 50 % in this case and indicate the aperture change. One reason why I chose to purchase a Sekonic meter over a Gossen or Kenko was that Sekonic reports % Flash in 10% increments (on models that have that feature). I purchased a used L-358 Sekonic.

• John

--
"[If you don't sweat the details] the magic doesn't work." Brooks, F. P., The Mythical Man-Month, Addison-Wesley, 1975, page 8.

Thanks everyone, particularly John and RDKirk. The link to Flash% was particularly helpful.

I have the KFM-2100 instruction manual, and was "aware" of the flash analysis display (the pie cut in four quarters) but obviously did not grasp its significance! So the light meter in flash mode measures both flash and ambient light. That explains why reducing flash power has no effect once I am recording 100% ambient light (i.e. F10.) Also, because the flash is only a portion of the total light exposure (flash + ambient) doubling the flash power results in less than a full stop of increased exposure (the amount depending on the percentage the flash is contributing at that point.)

I do macro photography indoors and I like to use the light meter to get a baseline flash level for the key light and when I add fill lights. I was used to flash and camera adjustments following the expected mathematical relationships, since ambient light was not an issue.

Again, thanks for the helpful comments.

Thucydides2 said:

It seems like the meter is reading both the flash and some ambient light.

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Yes

Thucydides2 said:

This is not a problem indoors.

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Lower ambient.

Thucydides2 said:

Is this to be expected

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Yes