Here is what I would do:
In the Export dialog box, under Image Sizing, check "Resize to Fit" and then set the dropdown to Long Edge, set the size underneath that dropdown to 1200 pixels, limit the file size to 500kb, check "Don't Enlarge" and see what happens.
Why do you have to reduce them to 500px?
What size in pixels are they?
thanks I will try this
the web site I have is suggesting that I reduce my photographs to under 500kb as anything bigger is too large for the site