I'm very new to Aperture, and am still struggling with stacks, though. My problem is that I'd like to put multiple versions of a single photo in a stack, cropped for different print sizes (with keywords of "5x7", "8x10", &c). But I also want to use stacks for selecting the best shot of several similar ones. My problem comes when I want to do both: Stack several shots together, but have multiple versions of the "pick." How do you do this without getting very confused?

[Update: A reader pointed out to me that filters on regular albums do include stacks that have members matching the filter. This behavior is not the same as projects (no match) or smart albums (match and extract images). I have amended the article to include this].

It is not obvious, but Aperture already does this for you: if you put images in a stack and then create versions, those versions are grouped with the originals. But there is a twist: if you leave the variations in the stack then a regular project filter cannot find them. The only way to find them is with an album: a smart album will find and extract the images; a regular album will find the images in the stack, but not extract them.

Look at this rather contrived example. Here are four images in a stack, with the pick on the left:

I want to manage two different crops of each of these. I'll make the crops really obvious so they can be distinguished in this example: one set of crops will be vertical and the other set horizontal. In real life they would have more realistic aspect ratios. I will start with the pick. I duplicate the version and drag it out of the stack (option drag does that in one step):

Then I crop it and keyword it:

Then duplicate the same original with option drag and crop it again, this time vertically, and keyword it:

Now I repeat that for the other images in the stack, just leaving them loose in the project:

A big mess. But that is OK because they are tagged and have the same file name as the originals. I can still find anything I need.

To find all the cropped images based on, say, the third image in the stack I have to do some filtering. Selecting that image and bringing up the inspector with control D lets me look at the file name (add the file name to the display using instructions here if it is not visible):

I copy the file name from the field: "Pine tree chopping22.JPG" and paste it into the project's filter dialog in the Other Metadata section:

And select is as the condition:

Here are the resulting images:

Notice that the original does not show up. That's because it is inside a stack in a project -- and only albums can see inside stacks. That is why I left the cropped versions loose in the project.

That found all of the crops based on one image, now what about the opposite: all of the images with one crop? To find all the horizontal images I filter on that keyword in the project. Since the cropped versions are loose in the project they are found:

Now let's do an experiment and see what happens if I tidy up the loose images. I select them all and hit command K to create a new stack:

Those grey rectangles inside the new stack have collected together images that are derived from the same original. What happens if I drag all of that stack into the original stack? This:

The originals and their versions are neatly grouped together! This is great, except that filtering the project on Horizontal now gets me this:

Nothing. Since this is a project filter and the pick does not match Horizontal, the whole stack is ignored. So I have to create an album.

A regular album will find any stacks that include the keyword, but will not extract the images. This tells me where to look, but not what to look at. In this case it is not very useful because every stack with a horizontal crop will be included along with all the other crops available in those stacks.

A smart album will match the keyword I specify and will extract the images. To create the smart album I select the project (important because I want the scope of the filter to be limited to that project):

And select the keyword I need, and check the Ignore Stack Groupings checkbox. That is the magic that lets the filter look inside the stacks and extract the images:

And as you can see, the four horizontal images have been displayed. But now I have lost my stacking information: which one was the pick? That is an inconvenient, but not unworkable problem.

So there are some trade-offs in the way that Aperture has implemented filtering and displaying stacks. I would do everything inside the stacks and have no loose images. I say that because the most important selection will be of the image. The crop follows. Once you have found the image in the stack that you want you can click on the crops and look at the metadata to pick the one you need.