In my previous post, I mentioned that I'm a little obsessed with protecting highlights from overexposure, and how I underexpose in situations where the dynamic range is high and/or the camera's meter might be mislead by darker areas in the frame*, to recover the shadows in post processing (with an emphasis on Lightroom 4). In this post I want to talk about an underestimated helper with protecting highlights that's built into all recent Nikon DSLRs: Active D-Lighting (ADL).
Preliminary note: everything that I describe below was tested on my D700, and verified on Shuwen's D90. Results may vary with other cameras.
Before I go into further detail, allow me to remind you that controlling and verifying an exposure with the histograms as precisely as possible requires using UniWB and a linear tone curve in the camera. Modern cameras can capture an astonishing dynamic range (in the area of 12 to almost 14 stops) in a single exposure when using the raw format, and Lightroom 4 is an excellent tool to compress all that dynamic range into a visually pleasing image, but to really utilize it to the maximum, it's crucial to get the best possible exposure (commonly referred to as "expose to the right without blowing the highlights").
But on to the meat of things. Over the years, my experience with Nikon's matrix metering (which is what I'm using most of the time) is that it has a tendency to expose rather rich, which for me often leads to the loss of highlight detail. The D80 has been especially prone to this, with it's matrix metering apparently giving even more weight to the active focus point than on previous cameras.
Active D-Lighting is exactly the feature that is needed to counter that problem. It was first introduced with the D3 and D300. Unfortunately, it also seems to be one heck of a misunderstood feature - "the interwebz" :P are full of examples of these misunderstandings (no links, no calling names here... just do a Google search for "Active D-Lighting" and read through the articles on websites, and the questions in photography forums). And that's bugging me, because ADL is so useful for me. Hence this article.
A bit of history (and perhaps an explanation where the confusion comes from). Before the D3 and D300, there was only "D-Lighting", which was (and is) a post processing feature built into cameras (I think from the D80 on, in the retouch menu) to help with high contrast scenes. Why anyone who uses raw data would do that in the camera is beyond me, because the result of using the retouch functions is always a JPEG image. We're using raw, and we're interesting in protecting highlight detail from overexposure, so lets just forget about it.
Active D-Lighting on the other hand is two-parted. "Active" + "D-Lighting". I kid you not. What this combination does is:
- underexpose a scene if highlights are detected by matrix metering (more on that in a moment). It affects the metering itself, which means it does affect raw files as well, of course. We can think of the "Active" part as an automatic exposure compensation to further protect the highlights.
- lift up the shadows with the "D-Lighting" technology - and this part obviously only affects the JPEG files coming directly out of the cameras processor. See above.
The state of Active D-Lighting is stored inside the proprietary Nikon NEF raw file. Only Nikon raw converters (Capture NX, View NX) can read that information, and will add the "D-Lighting" part automatically as you open the raw files on the computer (it can be turned on or off, of course). If you're using other raw converters (like Aperture, Lightroom, ACR, whatever), you'll have to adjust the shadows yourself. None of these do the D-Lighting part of ADL.
Active D-Lighting has four settings: Auto, Low, Normal, High. As I already said: the "Active" part affects the metering, so these settings are not just about how much the "D-Lighting" part lifts up the shadows. On Shuwen's D90** is a fifth setting, "Extra High" - it didn't have any different effect on the metering, so I assume that it only lifts up the shadows more. I didn't investigate the "D-Lighting" (passive, lifting the shadows after the fact) part of the process at all, since it only affects JPEG, and neither of us is using JPEG.
I was curious to find out if these settings would simply translate into exposure-compensation like stops, so I made a couple of tests - and the answer thankfully is: NO. The ADL settings do not directly translate to a certain amount of underexposure. It depends on the type of scene that the camera's matrix metering sees (ADL only works in matrix metering). They're more like "preference settings": when set to "High", it means that you prefer to have more highlight protection, when it's set to "Low", it means less so (and when it's set to Auto you'll never know what the camera thinks you prefer;).
Here are some of my results:
- making a photo of a small, brightly lit window from inside an otherwise dimly lit room led ADL on "High" to underexpose by 1 full stop.
- pointing the camera at a brightly lit scene (the type where you normally dial in some overexposure to compensate) with ADL on "High" resulted in the camera underexposing by just 1/3 of a stop.
- looking at an averagely and evenly lit scenery, the difference between ADL set to "High" and no ADL at all was - zero.
I stumbled upon one particular misinformation on the web: that ADL would not be active in fully manual mode. That is not true for my D700, or for Shuwen's D90. When ADL is on, it affects matrix metering in all modes, no matter if it's P, A, S or M you're using.
Also, there are situations where you do NOT want to use Active D-Lighting. Simply put, that's whenever you do NOT care about the highlights. As simple as that. A direct light source in the frame will be identified as a highlight, and ADL will compensate, which is totally unwanted for indoor or night photos (think about parties and events, concerts, sports). Also outdoor portraits against highly reflective surfaces, like a mirror facade of a building, or sunlight glistening on the ocean will trigger ADL. Turn it off in these situations (or switch to center weighed metering).
So - when I'm hiking and photographing landscapes, I always have Active D-Lighting on, and set to "High". I told you I'm a little obsessed with highlights! This setting takes a little worry from me, making it so much easier to protect the highlights. It spares me the "expose, check for blinkies, correct, expose again" routine most of the time, or wasting exposures, time and memory with bracketing.
Let me say it once more: it's no problem to raise the shadows by at least 1 stop - the only price you pay is a little more noise. But if you're at the brickwall of pure white, overexposed areas, reducing them by 1 stop won't give you back any detail. What's more, near the limit to overexposure, one channel might blow out a little earlier than others, and when you try to salvage the highlights, you'll get false colors (ever had a cyan sky instead of blue? yup, that's a blown out blue channel). Do the right thing: protect the highlights, recover the shadows***. ;)
And now: happy photographing!
*) It takes time to gain the experience when that will be the case, and knowledge of how the camera behaves. Allow yourself time to learn how the camera behaves. Be patient. It'll be worth it.
**) The D90 has another interesting setting: ADL bracketing (custom setting e4). It's the easiest way to compare how the camera exposes with ADL on and off.
***) I wrote about shadow recovery before: here.