Blury images

Enfold on Default takes for the lightbox-images not the full but the large images. These image formats are defined in functions.php on lines 174ff
( i just removed the comments) just for info:

$avia_config['imgSize']['widget'] 	= array('width'=>36,  'height'=>36); 
$avia_config['imgSize']['square']  = array('width'=>180, 'height'=>180);
$avia_config['imgSize']['featured'] = array('width'=>1500, 'height'=>430 );
$avia_config['imgSize']['featured_large'] = array('width'=>1500, 'height'=>630 );
$avia_config['imgSize']['extra_large'] = array('width'=>1500, 'height'=>1500 , 'crop' => false);
$avia_config['imgSize']['portfolio'] 	= array('width'=>495, 'height'=>400 );
$avia_config['imgSize']['portfolio_small'] = array('width'=>260, 'height'=>185 );
$avia_config['imgSize']['gallery'] = array('width'=>845, 'height'=>684 );
$avia_config['imgSize']['magazine'] = array('width'=>710, 'height'=>375 );
$avia_config['imgSize']['masonry'] = array('width'=>705, 'height'=>705 , 'crop' => false);
$avia_config['imgSize']['entry_with_sidebar'] = array('width'=>845, 'height'=>321);
$avia_config['imgSize']['entry_without_sidebar'] = array('width'=>1210, 'height'=>423 );
$avia_config['imgSize'] = apply_filters('avf_modify_thumb_size', $avia_config['imgSize']);

these image-sizes are generated from Enfold on uploading it to media-library.
WordPress itself generates 3 additional image-sizes:

Thumbnail (on default : 150px square or 80px)
Medium (on default : maximum 300px width and height)
Large (on default : maximum 1024px width and height)
Full (full/original image size you uploaded)

But: Enfold has some filter to change the format of this image for the different uses.
One is: avf_avia_builder_helper_lightbox_size
Another one is: avf_avia_builder_masonry_lightbox_img_size
Or: avf_avia_builder_gallery_image_link

How to use the filter : over child-theme functions.php:

function change_lightbox_size() {
    return "full";
}
add_filter('avf_avia_builder_helper_lightbox_size','change_lightbox_size', 10);

function avia_change_masonry_thumbnail_link($size){
  return "full";
}
add_filter('avf_avia_builder_masonry_lightbox_img_size', 'avia_change_masonry_thumbnail_link', 10, 1);

function avia_change_gallery_thumbnail_link($link, $attachment, $atts, $meta){
    $link = wp_get_attachment_image_src($attachment->ID, "full");
    return $link;
}
add_filter('avf_avia_builder_gallery_image_link', 'avia_change_gallery_thumbnail_link', 10, 4);

do not forget to empty all caching plugins and if you merge js and css files in Enfold to regenerate these files.