Smaller resolution for background images in a collection list?

Hi everbody,

I am working on a website for a construction company. All CMS collection pages include a collection list, that works like a gallery. Technically each collection item contains a Lightbox link, which gets its BG image from the collection. Everything works fine, just the “thumbnails” take way too long to load… Obviously the images are loaded in full resolution. There is probably no chance to get the system to create smaller images and display full resolution only in the Lightbox?

Here’s my read-only link: