• D7000 dynamic range for highlights

    Nikon D7000 owners everywhere seem to be raving about their newly found dynamic range, with all sorts of silly claims about all the over/under-exposure one can do and still get a serviceable photo out of this great little camera. As pleased as I am with this camera, I cannot share this enthusiasm when it comes to preserving highlight detail. At the end of the day, getting the exposure right, at least within reason, is still the best approach.

    To show what I mean I set up the following side-by-side experiment with the D300 and D7000. To get the baseline exposure, we spot meter to place the whites in zone VII. Then, in the subsequent exposures for each camera, we over-expose by 1 and 2 stops, applying corresponding correction of -1 and -2 EV in ViewNX to see how much white detail we can recover. Based on these results, I don’t think I would ever want to place my whites beyond zone VIII, and just to make sure, I’ll keep them in zone VII unless pushing the exposure harder is absolutely necessary.

    D300: 1/4 sec, f/8, ISO 200 D300: crop
    D300: 1/2 sec, f/8, ISO 200, -1EV of PP compensation D300: crop
    D300: 1 sec, f/8, ISO 200, -2EV of PP compensation D300: crop
    D7000: 1/2 sec, f/8, ISO 100 D7000: crop
    D7000: 1 sec, f/8, ISO 100, -1EV of PP compensation D7000: crop
    D7000: 2 sec, f/8, ISO 100, -2EV of PP compensation D7000: crop

    You will note a slight shift to blue in the 2 stop over-exposed shots. This is probably in part due to the way ViewNX applies negative compensation, but is nonetheless a good example that there is no free lunch for not shooting the correct exposure.

  • The Virtual GND (VGND) filter

    If you have ever dealt with hot sky that led to over-exposed highlights and/or under-exposed shadows and have wondered whether you should run out and buy an Graduated Neutral Density (GND) filter, you might want to see whether an alternative solution is available to you. We have all seen terrific exposures made possible through the judicious and skilled use of GND filters, but GND filters can’t handle every situation or require compromises to be used for some scenes. For instance, if the dark-to-bright line occurs along a jagged mountain top, how would you align the filter’s straight dark-to-bright line? Complicated geometries will require compromise or abandoning the use of the filter altogether. What if we used a post-processing technique that allows us to achieve a Virtual Gradual Neutral Density (VGND) filter?

    Let’s look at this next sample image as test case. The first image is the middle exposure for 3-shot HDR bracket, and a compromise between sky and shadow areas has led to some problems. The second image is the HDR composite image: better in the shadows, but still not quite there, and pushing out the shadows (not shown here) any further leads to image degradation. The final image is a straight horizon virtual GND image, where below the buildings we use the bright frame from the 3-shot bracket, and for the sky we use the middle image in the bracket (i.e., the 0EV image), using two layers and a masking technique to blend the two exposures. The dark exposure is used in the background layer and the bright exposure is used for the foreground layer. By selecting and removing the sky from the bright exposure in the foreground, we are left with a composite that includes a brighter foreground (water, sand, etc.), and a well-exposed sky, for a more balanced composite exposure.

    Original HDR VGND

    As you will notice, the VGND version shows more detail in the foreground while preserving good balance in the sky’s exposure. When compared to the HDR version, it also shows less blurring in the surf. And for what it’s worth, this particular image used the equivalent of a 1.3 stop GND. Have you seen any of those on ebay?

    Now let’s look at a far more complicated example, a very challenging exposure of a bright early morning scene. Again, the first two images show the original, as-shot middle exposure and the HDR version blending a 3-frame bracket. The third image uses the VGND technique, but with as complicated a mask as you can concoct, isolating the shadow areas in the foreground from the bright areas in the middle and background. Once more, the shadow areas use the +1.3EV frame in the 3-frame bracket, while the midtones and highlights use the 0EV (centered) frame. Combining the two yields nice detail in the shadows in the foreground and calm highlights in the rest of the scene. The only trick here is that your masking technique has to be spot-on, and unfortunately, the author is still fine-tuning his skills in that department.

    Original HDR VGND

    If you go pixel peeping, I’m sure you can find some imperfections in these VGND images, but don’t attribute those to the method or concept behind it. With better masking technique, even better results are possible. Bottom line: when you encounter a difficult exposure, namely one with a lot of dynamic range, take a 3-5 frame bracket, and when you get home, try both the HDR and VGND approach and see which you like best.

    Updated Aug 5, 11:20 PST with italic and underlined text.

  • The quest for the correct exposure

    What is the right exposure? This question comes up often, especially when wondering whether the camera’s meter and automated mode has let us down. As Bryan Peterson writes in Understanding Exposure: “…[exposure] comes up most often as part of a question — a question I’ve heard more often than any other: ‘Hey, Bryan, what should my exposure be?’ … And my answer is always the same: ‘Your exposure should be correct!'”

    “Correct,” Peterson goes on to demonstrate, depends entirely on what you are trying to accomplish. In fact, right after this quote he shows a “correct” exposure where the subject, a man, is in shadows but well exposed while the background is severely blown out. Oh, my, what would the Matrix-metering detractors do with such a shot if their Nikon D80 or D90 had exposed likewise?

    To illustrate the challenges that both photographer and in-camera meter face, let’s look at an example where, with a much maligned D80, we placed the focus point on the subject, we set the aperture to f/8 and ISO 100, and let Matrix metering give us the shutter speed. We snap the shot, and sure enough, just like everybody says, the background is blown.

    Maybe we should spot meter on one of our usual suspects, moving the focus point around until it lands on some of that blue water in the background. We set the shutter speed accordingly and press the shutter, only to find that now the background is well exposed, but the vase is almost a silhouette.

    Well, maybe we should spot meter on the vase and see how that turns out. We do that and discover the background is even more over-exposed that in the first photo.

    You may start to realize that with this lighting situation and others like it, you, the photographer, will have to make a compromise. How you arrive at this compromise will depend on what is important to you in this image. Do you want a beautifully exposed background? Or is the foreground vase more important? In short, what is this image about?

    You could say that it’s about the pretty blues and greens in the background. Alternatively, you could reason that the vase is the subject, and its surroundings, though necessary for the overall look of the image, are secondary. There, you made a choice. Now take it a step further: if the vase is what matters, how do you want it to look? You think about and decide that you like how the back lighting and how it shows off those nice amber hues.

    With that choice, it looks like the second shot is the best compromise, but you are not satisfied. The bright background is really too distracting. If the point of this image is to portray the vase, you don’t want anything to take away from it. Do you have any alternatives? You do. One would be to wait until the sun goes down a bit and see if that helps us in the background. As you think about it, though, you realize that the vase will also get darker. That gives you an idea. You have to add light to make this work. If you used the exposure setting for the second sample above, but added some light in the foreground to bring out the vase, how would that work? Here’s one try, with bounced flash to keep the light as natural as possible. You see some improvement, but the nature of the lighting (front-lit vs. back-lit) doesn’t quite give you the look you want.

    Another option is to select the first exposure, which thanks to Matrix metering’s inclinations, is over-exposed by +0.7EV in the background, and in ViewNX, pull the highlights down with -0.7EV compensation and push the shadows out with shadow protection. The result is acceptable, and very little noise has crept in the shadow areas.

    Still seeking that perfect exposure, you decide to give HDR a try. HDR has gotten a bad name thanks to a slew of cooked up samples, but you are very conservative in how you use it, and achieve the following result with a 3-exposure bracket.

    You may have noticed that in this discussion, we started with a question about what constituted the right exposure, which we went on to answer by other means, namely what made this a good photograph. And that’s Bryan Peterson’s point. You can’t know whether you have the “correct” exposure unless you first know whether you have the intended photograph. This is why metering often frustrates us. No algorithm in the world has been programmed with our personal intentions in mind.

    As a final observation, perhaps you agree the last two images offer the best balance between lighting and the goal we set out to accomplish in this photo. But it took post-processing to achieve these results, and you may find that distasteful because for some reason you believe every shot should come out of the camera perfect and ready for prime time. I advise you to jettison such a view-point. When the lighting is tough, you will have to use all the tools in your kit, and you better have post-processing as one of them. In fact, with experience you may find that as you approach shots like these you will start making them with post-processing in mind.