Enable RAW Rendering: check this box to render RAW previews. This is helpful if you have made changes to the RAW files in other products, such as Adobe Lightroom®. You can either use the Built-in Renderer or Adobe DNG Converter. If you choose to download Adobe DNG Converter, you need to specify where the app is located on your computer.
Render Cache size: If you have a large drive with available free space, you may increase this number, especially if you use files that are slower to render, such as HIF. Your preferred settings depend on your workflow.
Someone who uses the render cache with Adobe DNG Converter to get full-sized previews and revisits folders frequently would benefit from a larger render cache. That way, when they revisit a folder their computer doesn't spend energy creating another preview for those images. Someone who simply opens a contact sheet, finishes editing, and sends everything over to an external editor and never looks at those images in Photo Mechanic again does not need a large render cache. It would just use up disk space.
Remove cached files that are older than ___ days old: use this checkbox to specify how often you want to purge old files. If you use a larger cache size, you may want to do this more often to avoid filling your drive.
Empty Now: Clear the cache now. This deletes the render cache and does not delete any photos.