As I have mentioned in a couple of my PDF's on Aperture, I make extensive use of stacks. Not just for Album picks or multiple takes on the same image as discussed in my previous quick tip but to help get to my â€œselectsâ€ when I have shot many variations of the same subject. Here is how Apertures stack mode helps me do that. First off I group my similar shots together in a stack using the auto-stack feature. You can do this in the import pane of after the fact when you are looking at images in the browser. Don't be afraid that using the image date and time may make a couple of errors when stacking your images together. The process is highly interactive, you can see what it is doing as you drag the slider control. It almost doesn't matter what you shoot, auto-stack is useful. Try it. After you get either close or perfect stacking just go through all of the images once in the image browser with all of the stacks open and do some manual tweaking using some of the stack commands that you may not be super familiar with. Things like split stack, extract item, etc. My preferred method are the short cut keys. Once you get a feel for these commands you will probably love auto-stack because you will make completely different decisions that you may at first, like going over board rather than under-doing it because it is so easy to split one stack into to or to extract an image from the middle, etc.
Once I have my stacks I can get to my stack picks, the ones that represent the best and show up when stacks are closed extremely quickly using stack mode. It's easy to turn stack mode on just go over to the button on the right above the filmstrip that looks like a TV set and use the drop down to choose stack or better yet hit option-T. You can do this when viewing the filmstrip and the viewer but I prefer fullscreen mode so I hit F. Now for the good part…
In stack mode you will see two images at a time. On the left will be the current stack pick. On the right will be the compare image. If you like the compare image better just hit the command-\ and the compare will become the stack pick and will now be on the left. The image on the right will now be the next one down the stack. If you want to leave the current stack pick alone just hit the right arrow key to move on down the stack. When you get to the end of that stack the right key won't do anything any more. Hit the down arrow to go to the next stack. The key to using this effectively is to get your stack picks before creating new versions.
Another tidbit. When you are comparing images like this try hitting the Z key. This zooms into 100% view on both images you can scroll them around at the same time by using shift-command-space and drag. This is usually much faster for me to evaluate sharpness between two images or compare details rather than moving the loupe around between the two.
Comments and critique always welcome. MobileMe comments have been really flakey lately so you can email me.