Workflow & Technical Issues

Exposure and Metering.

boat

After Friday’s post on how I deal with white balance, I got a nice email from Ryan Marco asking me about how I go about metering. He asked a lot of good questions about how I determine where and how I meter the light in a scene. Many of you might have the same questions. And I’m about to disappoint you with my answer. I just point the thing and shoot.

First some background. When I shot film I got very good at taking readings off anything that was middle grey, or close to it, and then, using the Zone system, making adjustments from there. Those were simple times. I never used a handheld spot meter, never got too bent out of shape about things, and bracketed a stop in either direction when in doubt. It didn’t hurt that I was using mostly negative film with a broad dynamic range.

So when I tell you my approach to metering in digital leans to the side of simple, you know the background. As with white balance issues, life is just too short for neuroses on this matter. I lean towards the artist more that the geek most times anyways.

But here’s the bigger issue; it doesn’t matter. I suspect I’m going to get in trouble for this, so the caveat is that this is what works for me. But the thing is, digital capture is different than film. What matters, assuming you’re going to take the digital negative into the digital darkroom, is getting the best digital negative. The best digital negative is not the one that looks perfect on the LCD screen. It’s not the one where you nail the exposure using a spot meter. It’s the one (wait for it, this is paradigm-shifting stuff, here) that has the most digital information, even if it looks like crap on the LCD.

I cover this in Within The Frame (pg 44-46) but let me take another stab at it here.

The more digital information in that digital negative, the more able you are to create a final print with greater quality, less noise, and more awesomeness. So before I go into this, you need to remember: the image on the LCD will most likely look like crap. That’s OK. Use the LCD to preview composition and focus, and then pay attention to the histogram to determine exposure.

How do you know you have the best possible digital negative with the most digital information? The histogram. Forget studying your metering modes and learning the fancy voodoo light mojo. Learn to read your histogram, that cryptic graph of peaks and valleys on the LCD screen. You might have to consult your manual to find out how to access this. For most Canon DSLRs you just press the preview/play button and then the info button once or twice until your histogram appears.

histogramThis is the histogram from Adobe Lightroom, but the one on your LCD will look similar. The histogram above represents a scene captured with no blown highlights – notice the mountains and valleys don’t go off the right-side of the chart – and no plunged shadows – notice the data doesn’t go off the left-side either.

Now, I’m going to assume you know nothing about the histogram. It’s a graph, that’s all it is, and it’s deceptively simple. that graph represents the light values in the scene you’ve just captured at the exposure values you’ve captured it at. On the far left are shadows with no details, totally plunged shadows of darkness. On the far right are highlights with no details, total burned out whiteness. And between those two extremes are all the tonal values from black to white. The height or shapes of the peaks and valleys, for this exercise, don’t matter. Ignore them. You can do something in-camera with where the peaks and valley sit from left to right, but can’t do a thing about their height or shape. That’s the scene. Ignore it.

Why the histogram matters now gets – for a moment – a little more complicated. It’s logical that as long as you get the whole scene into the box of the histogram – neither wildly over nor under-exposed – you can tweak the rest in Lightroom and be done with it. Simple, perfect exposure, right? Wrong. You’ve created a digital negative but not a good one. Why? Because the histogram reflects some quirky math that can only be understood by wizards and occultists, and it doesn’t respond to the logic of mortals like you and I.

Remember I said the best digital negative was the one with the most information? Well the right half of the histogram is capable of storing exponentially more information in it than the left half. WAY more information. And the right quarter of the histogram, WAY more than the other three combined. How much more? Again, I’m simplifying, but if the right quarter of the histogram can hold 2000 levels of information, the quarters to the left of it can hold 1000, 500, and 250 respectively. There isn’t much information at all in the darks. That right quarter of the histogram can hold twice what the rest of the entire histogram can hold.  It’s a WAY bigger bucket, can hold more information. More information means better image quality and more flexibility in the digital darkroom before noise becomes an issue.

So what do you do with this knowledge?

Here’s how I approach exposure. First, I shoot on AV mode or Manual almost 100% of the time. I leave my metering on whatever your camera’s equivalent of centre-weighted average is. Then I take the shot. Click.

Before you look at the images/histograms: I did this in Lightroom as a simulation only and it’s meant to be an illustration, so don’t get hung up on the EXIF displayed on the histogram, it won’t change and will only confuse you. Look at the image relative to the how the information is distributed in the histogram.

exposure1

I look at the histogram. Way too dark. Barely has any information in the right half, never mind the rightmost quarter. Then I use the EV+/- function on my camera, push the exposure a stop, try again. Click.

exposure2
Getting better. But while the image LOOKS OK-ish on the LCD screen, the histogram is telling me otherwise. It is still, in terms of a good digital negative, underexposed. So I go back to my EV +/- and bump it another stop. Click.

exposure3
Much better. Might be a little light for my taste, and where’d my clouds go? Doesn’t matter, I know they are there because none of the scene has disappeared off the edges of the graph. You’ll bring them back in Lightroom or Aperture. Look at the histogram – it’s where it should be, as far over to the right without going off the end. What matters is that now you have LOTS of digital information.

Now I have a digital negative with as much information as possible I can bring the image into the darkroom and adjust it as necessary. In this case I like the luminosity of the boat and the ocean but it was the clouds in the initial scene I loved and have lost. Should have had an ND grad filter in my pocket but didn’t. So in this case I’ll use the gradient filter in LR to darken the sky and punch the clouds – Clarity rocks for this. I’ll make a few more tweaks – including a grad filter along the bottom with Clarity set to -100 to soften foreground waves, and the brush tool with bumped exposure, brightness and clarity to pop the sails.

Here’s the final image (crappy composition and all)

boat-final

So the name of the game is getting to know your histogram so you can create the best possible digital negative. And the best possible digital negative is what, class? The one with with the most information. There will be times when you have a scene with a larger range of tones than the camera can capture. In this case you have options; several of them. Decrease that range with the use of ND grads to reign in the highlights, or a flash to pop the shadows. Or you might take 3-5 bracketed exposures and bring them together in Photomatix or Photoshop. Or you can just make a choice to create an image with either plunged shadows and/or burned out highlights. (page 45 in Within The Frame has a great example of an image with a histogram that goes wildly off both ends.)

My way isn’t the only way, I’m sure of it. But it’s what works for me. I used to meter then shoot, now I shoot then meter. “Same, same, but different,” as they say in Asia. Does this help? Questions?

If this was helpful and you want more, or if my lunatic ravings didn’t convince you, I urge you to spend $9.95 and download Darwin Wiggett’s article Expose Right. You can find that article HERE on Darwin’s site. Highly recommended.

Apr 28th

2009

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Sharpen the tools

On the Artist – Geek continuum I am closer to artisty-fartsy than I am to techno-nerd. My eyes gloss over when things get too technical. As a result, my weakness where this craft is concerned, is keeping my chops up and learning new skills. I’m big on vision and I talk ad nauseum about it, […]

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