Explore Scientific ED80 focusing issues with a DSLR

Has anyone that uses an Explore Scientific ED80 refractor ran into focusing issues when using a DSLR? I'm currently using an older Canon EOS 40D and I cannot focus an image to save my life. I have both extender tubes attached (two came with the telescope) and I notice it starts to get into focus the further I extend the camera away from the telescope via the focuser knobs.

However, when I extend the focuser knobs out as far as they go the image is still almost unrecognizable. I tested this out on the moon and it's incredibly blurry but looks perfect with a 25mm and a 10mm eye piece.

Do I need to purchase a 3rd extender tube for my scope? And if so, is this normal? I wasn't sure if the added length would add worries due to weight distribution.