I've talked about Smart Objects in other posts, but this is about nesting multiple Smart Objects . Here's a super easy explanation why I use (and you should use) Smart Objects. I had the image completed and was looking it over for any flaws, omissions, extra bits, missing bits or whatever. The thing I noticed was that the ball, in flight, had shrunk from soccer ball size to softball size. It looked like she really kicked the air right out of the ball. Remember, this was just before I was about to pull the trigger on making a print. I typically print off the top set of Smart Objects. The top set of Smart Objects contains Sharpening and Vignetting only. Everything else has been done and work on the image is over. What a time to discover you have to make a correction two sets of Smart Objects down. But, because of Smart Objects, it's not a problem. It's actually an easy fix (and it would up being the second trip back to the base set) because of the flexibility of using Smart Objects. To find out why I'm so high on Smart Objects and to get an idea of the magic of Smart Objects, hit the "read more".
First thing to make note of is that there's three sets of Smart Objects in today's image. The first set is all the Layers and Layer Masks involved in assembling the image. If you count heads you'll see that there are seven individual Layers (actually eight, but more on the extra Layer later) used to make up the action sequence. I use a Nikon D300 and it can fire six times per second. Do the math. The entire sequence is just over one second. Six of the seven Layers have Layer Masks to go along with them. Each Layer Mask has an Alpha Channel that goes along with it. The Alpha Channels were made by using the Quick Selection Tool (W) to select the goalie in each frame and saved by right clicking on the selection and choosing "Save Selection". The reason for saving the selection before moving forward is so you can get the selection back by loading the selection (Select/Load Selection) rather than needing to reuse a selection tool (Lasso, Marquee, Color Range, Quick Mask, etc.).
So, the bottom set is the images required to make the image. Select all the Layers, right click and choose Convert to Smart Object. This reduces the eight Layers to one Smart Object. It now looks like you're back at a Background Layer, but with a twist. You'll see the notched corner in the lower right of the thumbnail indicating a Smart Object. The next set was to do any color correction (salt to taste correction) using individual Hue/Saturation Adjustment Layers (Red, Yellow, Green, Cyan, Blue, and Magenta). Once that's done we're back to having seven Layers. Select all of those Layers, right click and choose "Convert to Smart Object".
We're back to a single Smart Object being shown. Two copies of the Smart Object are made (CTRL J twice). Turn off the eyeball on the top Layer and select the next Layer down. It's already a Smart Object so we can go directly to Filter/Other/High Pass and do a High Pass Filter sharpening (change the Blend Mode to Overlay). Once that's done, turn on and select the top (unsharpened) Layer. Using the Marquee Tool (M), make a Selection. Leave a border around the focus area of the image. Hit the Layer Mask icon at the bottom of the Layers Panel. That will apply a preformed Layer Mask to the top Layer. You'll have to Invert (CTRL I [eye]) the Mask and then change the Blend mode to Multiply. The Vignette will (most likely) be too much. Lower the Opacity to taste. Thirty, forty of fifty percent is about the right range.
Thanks when I noticed the soccer ball being the wrong size. The flying soccer ball was actually the eighth Layer in the bottom set. Any of the "old ways" to get back there would involve a lot of redoing a lot of work. Using the left side of the keyboard method (CTRL/ALT/Shift/E) won't help a whole lot in this kind of situation either. Anything that needs to be done under the composite Layer means tossing everything above the composite.
Using nested Smart Objects makes it a simple fix. Double click on the base Smart Object. It'll open the Layers below. Double click on that base Smart Object and it will open the bottom set (in the case of today's image) of Layers. The flying ball was imported from another shot and was on its own Layer. Do a Free Transform (CTRL T) on the ball Layer and make the flying ball a similar size to the rest of the balls. Once that's done it's time to climb back up the Smart Layer ladder. Do a File/Save and let the computer cook. When you have your cursor back do a File/Close. Now we're back up one step of the Smart Object ladder. Do another File/Save and another File/Close and you'll be back to the finished image with the ball enlarged.
An excellent example of using nested Smart Objects.