In my photography I use Aperture Priority metering most of the time.  I take a shot, look at the histogram, and use Exposure Compensation (EC) to add or subtract light as needed.  Yes, this works great most of the time…but most of the time does not mean all of the time.  There are shooting situations where it is best to not use an autoexposure mode (aperture priority mode, shutter priority mode, or program mode).  This means selecting both the shutter speed and the lens aperture; that is, using manual exposure mode.  In this mode, you have to physically set both the shutter speed and the aperture, and the camera remains at those settings — and exposes at those settings — no matter where you aim the camera.  What you set is what you get, period.  EC does nothing to change the camera’s settings.  It affects the meter readout, but it does not in any way change the shutter speed or aperture on the camera, so turn EC to zero.  In manual exposure mode, what you set is what you get.  If you want to lighten or darken the image, you have to physically change the shutter speed or the aperture or the ISO.  The camera itself does not change anything.  What you set is what you get.

This blog post comes about because of a Joseph Van Os Photo Safari I recently led.  We were standing on the top of a cliff overlooking the ocean, preparing to photograph birds flying past.  If they birds were above us, the background was a pale milky blue sky.  If below us, the background was a dark navy blue ocean.  So what’s the right exposure?  Any autoexposure mode would be biased by which background was in the frame.  One solution would have been to work only those birds against the pale sky, or only those against the dark ocean.  But the birds were not cooperating in that manner.  They would swoop around, at one moment be above us and the next moment be below us.  When I mentioned that this situation called for a manually set exposure, to compensate for the different background tonalities, the response I got reminded me once again how many photographers have never used a camera in the manual exposure mode.

If the light remains the same, once you correctly set a manual exposure, it is correct for all subjects in that light regardless of their tonality.  OK, but how to set that exposure?  Pick something, it doesn’t matter what, in that constant light, and adjust for it’s tonality.  When you set the camera to manual exposure, an analog display will appear in the viewfinder with a “zero” point in the middle of a “plus” and “minus” line.  “Zero” is the starting point.  Change the shutter speed and/or aperture until this mark in highlighted, and you have set the camera to render whatever you aimed it at to be rendered as a medium tone.   Go to a “plus” mark, and you have added light.  Go to a “minus” mark and you have taken away light.   So, aim the camera at a single tone, and meter it and only it.  Physically change the shutter speed and/or aperture to render that area at whatever tone you want it to appear.  Here’s a quick and dirty way to think about this.  At the “zero” mark the camera will render that subject you metered as a medium tone.  At the “plus one” mark, one stop open, the metered subject will be rendered as a “light” tonality.  At the “plus two” mark, two stops open, it will be rendered as a “very light” tonality.   At the “minus one” mark, one stop down, it would be “dark” subject; at “minus two” it would be an “very dark” subject.

Suppose you meter a blue area.  Here’s what would happen as you change the shutter speed/aperture combination:

+3, whitish blue
+2, very light blue
+1, light blue
0, medium blue
-1, dark blue
-2, very dark blue
-3, blackish blue

Back to those birds….  The solution would be to pick an easy area to meter:  either the pale sky, or the dark ocean water.  Let’s use the pale sky; it was roughly “very light blue.”   Set the camera to manual exposure mode, aim it at the area of sky where the birds would be, and adjust shutter speed/aperture until the “plus two” mark was highlighted.   It doesn’t matter what combination shutter speed/aperture you use to get started.  Pick the equivalent combination that gives the shutter speed needed or the aperture needed.  Suppose you aimed your camera at that sky and the exposure combination that yielded “plus two” was 1/125 sec. at f/11.  Well, you know that 1/125 sec. is way to slow a shutter speed to freeze a bird in flight.  1/125 sec. at f/11 is exactly the same as 1/250 sec. f/8, or 1/500 sec. at f/5.6, or 1/1000 sec. at f/4, etc.  Need a faster shutter speed?  Raise the ISO one stop, and you could shoot at 1/2000 sec. at f/4 (or any equivalent combination).  Set the shutter speed/aperture combination you want to use, and fire away.  So long as those birds remain in the same light, and the light itself does not change, the exposure will be correct no matter the background.

I can think of a number of situations where using manual exposure would be best.  Consider working a black sand beach, with waves breaking white over it.  The camera meter would read a black subject at one moment, a white subject at another.  Or imagine you’re using a zoom lens to photograph a dark buffalo standing in the snow in Yellowstone.   As you zoom the lens, the image changes from primarily snow to primarily buffalo.  Or a situation I faced back in February while photographing red-crowned cranes.  The white cranes were standing in a snow-covered field, but as they took flight the background became leafless winter trees, a dark toned area, and then to medium blue sky as the birds rose higher.  In all three situations, so long as the light remained unchanging, the solution was to meter one area, set the exposure using manual mode, and shoot away.

If you’re not familiar with the manual exposure mode, I would strongly suggest some practice.  But let me add one final statement:  with all digital cameras, you cannot evaluate exposure or color via the LCD on the back of the camera.  The histogram is your friend, whether shooting manual mode or one of the autoexposure modes.  Learn how to use manual exposure mode, and learn how to read the histograms.

If you’re a RAW shooter you should already know about ETTR, Expose to the Right.  The theory behind ETTR is that the best image capture for the most possible information is when the histogram is pushed to the right, to the “bright” side.  Just keep adding exposure until that histogram is over to the right side of the graph.

OK, but how far to the right?  You definitely don’t want to clip the highlights.  DSLR cameras have a clipping warning display, the “blinking highlights,” or “blinkies” as they are commonly called, which shows up on the camera’s LCD.  Many cameras will even display the blinkies for each individual color channel, besides the composite luminosity.  But remember that the image displayed on the LCD is not the actual RAW file; it’s a jpeg thumbnail created on the fly by the camera.  Camera manufacturers have coded in some headroom with the blinkies, as they don’t want customers to be angered at blown out highlights.

Fine.  But I would suggest running a test to determine exactly what the correlation is between when the blinkies start, and the actual clipped highlights in the RAW file.  You can easily run a test to determine this.  Set your camera to Aperture Priority, lock it firmly on a tripod, and aim at any scene.  Increase exposure until the first blinkies appear.  Note this frame (probably the easiest solution would be to delete any previous frame you shot to get to this point).  Now shoot several more frames, using  Auto Compensation to add 1/3 stop to each successive frame.  Open this series in your RAW file software, such as Lightroom or Adobe Camera Raw, turn on the clipping warning in the software, and check each frame.  I’ll bet that the starting frame, the one the camera blinkies said was clipped, is actually not clipped at all.  In fact, you might be surprised at just how much headroom you have.  With my particular Nikon D800E and a medium toned test subject, I have to add 1.3 stops beyond the blinkies before the RAW file has clipped highlights.

So what’s the point of doing this?  Why worry?  Well, with digital capture, noise lives in the dark exposures.  If you want the best possible data, start with the best possible exposure.  With my particular camera I’ll add some extra exposure whenever the subject is such that I can, especially when working at higher ISO values where noice is always a problem.  Recently I shot a landscape at ISO 1600.  I shot at both the metered ETTR exposure, and at my “extra 1.3 stop” ETTR settings.  The difference was remarkable.  The first image needed noise reduction.  When I looked at the second shot, the one when I had added 1.3 stops, the image on the LCD appeared almost washed out.  But when I reduced the exposure in Lightroom (my standard RAW file software), all the noise was gone.  In fact, my tests suggest there is even a slight difference when the camera is set at base ISO 100, where I use the camera the most.

Does this really matter?  The answer depends on how compulsive you are about quality, the realities faced in the field, and on how the photograph is to be used.  Just remember, ETTR is for RAW capture only.  And  you don’t want to lose an image by blowing out the highlights.  There are indeed some scenes with the highlights already maxed out.

Once you know how the blinkies in your camera correlate to the actual RAW histogram, a simple and safe solution — particularly for static subjects such as landscapes — is to set your camera to bracket another  frame that is 2/3 stop more exposure than the ETTR histogram on the LCD.  When I shoot with my D800E, I know that I’ll be adding that extra bit of light whenever I can.