Metering Techniques:
Dealing with Backlit Scenes by Averaging Incident Light and Reflected Light Readings

Scenes that are backlit, or strongly side-lit, are very difficult to expose correctly. The high contrast light means that the brightest and darkest parts of the scene might fall outside the dynamic range of your digital camera.

A reflected light meter, like that built in to your camera, will underexpose the scene. The bright light from behind the subject will fool the meter, causing the backlit subject to render very dark, possibly so dark that little or no detail is visible.

A handheld incident light meter is usually the best type of meter for digital work because it ignores the subject and just measures the light that hits the subject. Normally, an incident meter cannot be fooled by very bright or very dark subject matter, as a reflected light meter can.

Backlit and strongly sidelit scenes are an exception. The incident meter is used by standing at the subject position and pointing the meter's white dome back toward the camera lens. The hemispherical dome simulates the three-dimensionality of an average subject; and it can take into account light from straight on, as well as side-lighting, if the lighting angle is not too severe. In a backlit scene, the whole dome is in shade and does not see the light coming from behind. The result is an overexposed photograph.

 

Solutions

One solution is to use a handheld spotmeter and carefully measure the brightness difference between the darkest and lightest parts of the scene that you want to retain detail in, using those readings to calculate exposure settings that will leave all or most of the scene's brightness range within the dynamic range of your camera's sensor. This works wonderfully, but is cumbersome and is difficult for beginners as it requires some testing to determine your camera's dynamic range, and experience in knowing what areas to measure in the scene.

If you're interested in learning to use a spotmeter, I have a tutorial: How To Use A Spotmeter For Digital Photography.

 

An Easier Way: Incident-Reflected Average

A simpler solution is to take two readings with a handheld meter, a reflected light reading and an incident light reading. Then, you average them!

This technique is fast and easy to learn, and works well for most backlit and sidelit scenes. If the brightness range in the scene is very wide, you may have to use the shadow and highlight recovery sliders in your RAW processing software (like Lightroom or Capture One). This technique works best if you shoot RAW, rather than JPEGs.

This technique was invented in the 1960s by Jack Dunn, a British engineer who did pioneering research into exposure metering in the mid 20th Century. Dunn wrote, with George Wakefield, a book called "Exposure Manual." If you're as big of a meter geek as I am, you want to get hold of this book.

I also have a tutorial video on YouTube showing how I edited a photograph that I made using this exposure technique: How I Did It #3: Processing "House Moving" in Lightroom From Start to Finish (YouTube)

 

 

Example #1

Exposure of a backlit scene determined with a reflected light meter.

Exposure determined with a reflected light meter.

 

Exposure of a backlit scene determined with an incident light meter.

Exposure determined with an incident light meter.

 

The Results:

Exposure of a backlit scene determined with a reflected-incident average.

Exposure determined by averaging the reflected light and incident light meter readings.

 

Final image, after adjusting the shadow and highlight recovery sliders in Lightroom.

The final image after adjusting the shadow and highlight recovery sliders in Lightroom.

 

As you can see in the finished image above, this technique produced a beautiful rendering that has good detail in the highlights and shadows, despite the very high brightness range in the scene. It was very simple to do in the field, taking about 30 seconds to make the two readings and average them. Modern cameras have "Evaluative" metering systems (also known as Matrix Metering) that analyze the scene to compensate automatically for such difficult lighting situations. In my experience, they sometimes work well and often do not. The incident-reflected average technique has been far more accurate for me.

 

 

Example #2


Strongly backlit scene with a very bright sky with exposure determined by a reflected light reading.

Metered with a reflected light meter. The very bright backlit sky fooled the meter into underexposing the photo.

 

Strongly backlit scene with a very bright sky with exposure determined by an incident light reading.

Metered with an incident light meter. The sky is blown out, and even the sign is overexposed, since the shadowed side of the sign facing the camera has been lightened too much.

 

Strongly backlit scene with a very bright sky with exposure determined by averaging a reflected light reading and an incident light reading.

For this exposure, I took an incident light reading standing in front of the sign, then walked back to the camera and did a reflected light reading. I averaged the two readings, and this was the result.

Because of the very wide brightness difference between the foreground and the very bright sky, the average exposure gives dark tones that are slightly too dark and lights that are still a little too light.

 

Strongly backlit scene with a very bright sky with exposure determined by averaging a reflected light reading and an incident light reading, after using highlight and shadow recovery sliders in Adobe Lightroom.

The same exposure, but this time I used the Highlight and Shadow Recovery sliders in Adobe Lightroom to open up the foreground shadows and bring down the bright clouds. Midtones seem a little too dark, though.

 

Strongly backlit scene with a very bright sky with exposure determined by averaging a reflected light reading and an incident light reading, after using highlight and shadow recovery sliders in Adobe Lightroom and lightening it more using a curves adjustment.

The final image. I took the version with the adjusted highlight and shadowsliders and applied a curves adjustment to the image to lighten the midtones. See my Curves Tutorial for more on how to use curves in Photoshop, Lightroom, and other image editors that offer a curves tool.

Now it looks great! The clouds are bright but still have full detail, while the sign and foreground areas look like they should.

 

 

Example #3

Exposure of a backlit winter snow scene on a bright sunny day determined with a reflected light meter.

Exposure determined with a reflected light meter.

 

Exposure of a backlit winter snow scene on a bright sunny day determined with an incident light meter.

Exposure determined with an incident light meter.

 

The Results:

Exposure of a backlit winter snow scene on a bright sunny day determined with a reflected-incident average.

Exposure determined by averaging the reflected light and incident light meter readings. This is a straight, unmanipulated rendering. The only adjustments done to the RAW file in Lightroom were sharpening and white balance.

 

Final image, after adjusting the shadow and highlight recovery sliders in Lightroom.

The final image after adjusting the shadow recovery slider in Lightroom.

 

This was a very difficult scene because of the bright snow, and the fact that the sun was directly in front of me. The large amount of lens flare visible in the scene is an unavoidable consequence of shooting directly into the bright sun.

The challenge was to maintain detail in the snow, while still keeping it at a value that looks white. Too little exposure, and the snow will go gray, and too much will cause loss of texture and detail. At the same time, we want to have detail visible in the shadows.

The Averaged exposure actually works very well, without the need to do any further adjustments. If you want more shadow detail, pulling up the Shadow Recovery slider in lightroom produced the final result shown above.

 

 

Equipment Requirements:

Ideally, for this technique, you'll need a handheld exposure meter capable of both incident light metering and reflected light metering. The reflected light metering should not be a spotmeter, it needs to be a wide-area reflected light meter (30 to 40 degree measuring angle). This rules out many of the recent Sekonic meters, like the L-508, L-608, L-588, L-758, and L-858. The aforementioned meters have a one degree spotmeter as the only choice for reflected light metering.

Minolta meters like the Flash Meter IV, Flash Meter V, Autometer III, Autometer IVF, and Autometer VF can be used if you have the Reflected Light Attachment (the flat disk with a hole in it, not the spot viewfinders). That said, they're rather cumbersome to use in the field because switching from incident to reflected metering requires you to remove the white incident metering dome and replace it with the reflected light attachment. This is a bothersome two-handed job and if you're not careful you will eventually drop or lose either the dome or the reflected attachment, and they are expensive to replace.

My favorite meter for this technique is the long-discontinued Gossen Ultra-Pro (Mastersix outside the USA). The incident dome is made to simply slide out of the way to do reflected readings. You can do it one-handed, the dome cannot fall off, and there is no need for a separate attachment for doing the reflected light reading. Gossen has made many meters utilizing this simple method of switching from incident to reflected, including the old Luna Pro, and the later Luna Pro SBC, Luna Pro F, and Multi-Pro. I like the Ultra-Pro because it is a digital meter with a built-in averaging function that saves me from having to do math. It is relatively uncommon meter because back in the 80s and 90s when it was made, it was Gossen's top of the line meter, and it cost nearly $1000 when it was finally discontinued. I do see them on Ebay for around $100 fairly often.

If you have a good incident meter that doesn't do wide-area reflected readings, and you don't want to buy one, you can use your camera's built in meter for the reflected reading. You'll have to do the averaging math in your head. Make sure you do not have the camera set to use Matrix or Evaluative metering; the meter should be set to do centerweighted metering. That will give results similar to a handheld reflected light meter.

 

More Examples:

Here are some more more photographs that I made using the Incident-Reflected Average metering technique.

 

Example of a photo made with incident-reflected average metering.

 

Example of a photo made with incident-reflected average metering.

 

Example of a photo made with incident-reflected average metering.

 

Example of a photo made with incident-reflected average metering.

 

An Alternative Technique:

There is another option for determining exposure for backlit scenes. It is called The Duplex Method, and it uses only an incident light meter.

 

 

 

The knowledge that I am sharing took many years of study and practice to attain. If you find it valuable, please donate through my Paypal button below. My creative work is how I support myself and my son. Thank you!

 

 

 

 

 

©2018 Christopher Crawford

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