You don't convert to JPEG or any other format until there is some need to Export. The settings for that are handled in the Aperture Preferences/Export. The typical needs are full export, creating a new file to be sent to an external editor, or Email. Until that time, Aperture maintains Versions as an instruction list to be applied to the Master.
Otherwise there should be no need to convert. What did you have in mind?
A tool you might want to investigate is RawHide For Aperture. A native app and no scripting. You have fine grain control over the output JPEG which is automatically added to the project the original RAW image was in. There are also options to tag your original and copy, and/or set the original's rating to reject.
Please be aware that I am involved in this project, so take my recommendation as you will with this knowledge.
It can be done in Aperture. First select the RAW file(s) to be converted. Next click FILE->Export->Version. In the export pop up window choose "JPG Original Size" (or another size) from the Export Presets Menu. Pay attention to the naming and location choices. When ready click the EXPORT VERSIONS button and the JPEG file(s) will be created. You will have to import them to get them into Aperture.
But isn't there an issue about storing RAW files? I thought I'd store older RAW files on a hard disc in another building and just keep RAW to jpgs conversions and current RAW files on my desk top. The reason being, of course, that RAW files are so much bigger and thus take up storeage space on my machine. But I'm not sure how I can do this in Aperture. Is there a problem or am I being dim?
You can relocate the original raw images to a folder outside Aperture (for example on an external disk): Select the images you want to move outsied the library and use the command
File > Relocate originals
This will move the originals, but keep any jpeg previews. You can browse these previews, tag the images, rate them, use them in the Media Browser in other applications. Only if you want to export them or edit them, you need to connect the external drive. If you set your preview preferences to render high quality jpegs, you will have essentially what you want - high quality jpegs inside Aperture, and the raws safely stored away outside.
I find all this rather strange! I often convert RAW to Jpeg if I want to keep an image for reference but it doesn't merit or require the 8 to 10MB of the RAW file (on my computer, my external drive, or anywhere else). For example, I take photos of artefacts in museums, and I also photograph the labels/legends beside them, for reference. I can keep those solely as quite small Jpegs since I'm never going to want to print them.
(No, I don't want to switch settings on the camera while I do this - I'll only forget to switch back, and then have loads of low-res Jpegs that were meant to be glorious RAW).
In other software I've used, there's a batch convert that makes this very simple. Seems that in Aperture I'm obliged to export and then re-import. Not a big deal, but a slight pain in the arse all the same, and a little odd.
Anyway, thanks to the above posts, I now know how to do the export-import malarkey. I couldn't find it in the manual.
For example, I take photos of artefacts in museums, and I also photograph the labels/legends beside them, for reference. I can keep those solely as quite small Jpegs since I'm never going to want to print them.
I'm doing the same.
If I have many of them, I collect them in an album and export them all at once to batch convert them to a smaller sized jpeg, then reimport them.