Hi Mike,
When i look at the theme based image sizes it shows: thumbnail size = 260×260. So it looks like that should be a correct size.
The images i have uploaded are 640×640 so it seems like the theme is using a small thumbnail size and is stretching it somehow. Is there a way to stop this proces with css?
I just tried to regenerate my thumbnails using the plugin that you link to, but the images stay blurry.