Robbie, thanks for purchasing my Light & Land eBook. I hope you found it helpful. I certainly understand your confusion about this issue: everybody seems to do things differently, and you often hear conflicting information. Remember that there are really no right or wrong answers - these are all just tools, and you should use the tools that work best for you, and that you're most comfortable with.
Jeff, I've long admired your work, and all the excellent and helpful educational materials you've given us over the years. I hope to meet you one day and discuss Lightroom stuff, or maybe just shoot the breeze. Since I live just outside of Yosemite, let me know if you're ever headed this way.
So let me explain why I prefer using the Point Curve to set black and white points in Lightroom. Again, this is a preference, not a case of right vs. wrong.
It's true that with the Point Curve you can't hold the Option/Alt key to see clipping, as you can with the Exposure or Blacks sliders. But you can see clipping by clicking on the triangles in the Histogram, or just pressing the J key. Doing it this way also allows you to see the image as a whole, and judge the effects of setting the black and white points on the image as a whole, as well as seeing the areas being clipped.
And Jeff you're right, of course, that moving the black and white points in the Point Curve will affect the rest of the curve. That's one reason I always set the black and white points first, before placing other points on the curve. But I'd prefer to set black and white points first anyway before adding contrast or doing anything else with the curve, as setting the black and white points provides the foundation for the rest of the tonal adjustments. Also, by making all the tonal adjustments with the Point Curve I can do everything in one place, and see the interaction between the black and white points and the other points on the curve.
But the main reason that I use the Point Curve, and why I'm so happy that Adobe finally added this to version 3.0, is the difference in the image's appearance. Now as far as I can tell there is no difference between using the Blacks slider and pushing the lower-left end of the Point Curve to the right (as long as you keep this point along the bottom of the Curves box).
But there is a difference between using the Exposure slider to set a white point and doing it with the Point Curve. When Lightroom first came out Adobe said that pushing the Exposure slider to the right was the same as setting a white point with Levels or Curves in Photoshop. Maybe Adobe said that to justify not including Levels or a real point curve in early versions of Lightroom. But it’s not the same, and it’s easy to dispel that myth, especially now that Lightroom has a real point curve:
• First, find an image that has some room between the lightest pixels and the right edge of the histogram—in other words, room to move the white point before seeing clipping.
• Next, activate the clipping warnings by pressing the J key, or clicking on the right-hand triangle in the Histogram.
• Go to the Point Curve. Push the upper-right end of the curve to the left, making sure to keep it along the top of the box, until you barely see some clipping (with the clipping warning activated, this will show up as red spots).
• Make a Virtual Copy of this image, and reset the Point Curve. Then push the Exposure slider to the right until, again, you barely see some clipping.
• Compare the two versions. You’ll see that while the white points are the same—the amount that’s clipped to pure white in each version is the same—the midtones are not. Using the Exposure slider moves the white point, but also boosts the midtones. With the Exposure slider the image will look lighter overall, and while the brightest pixels in the histogram should be at the same place in both versions, the rest of the histogram will look different.
In some cases boosting the midtones like this is okay, but in many cases it flattens highlight contrast and washes out colors. The difference is more pronounced when the Brightness slider is set to its default of +50. Setting Brightness to 0 minimizes the difference between these two methods—it’s still there, but smaller.
I put a page up on my blog to show an example of the difference:http://www.michaelfrye.com/landscape-photography-blog/setting-the-white-point-in-lightroom-a-comparison/
I think this example makes the difference pretty clear, but I suggest (to anyone) that you try it yourself.
So Robby, I hope this helps explain the difference, and why I prefer using the Point Curve rather than the Exposure slider. Unfortunately I didn't have room to discuss this esoteric topic in the eBook, but you gave me an incentive to explain it on my blog, so thanks!
Jeff, again, I really appreciate all that you do. Maybe our little discussion here will help shed some light on this whole topic.