Front focus problem with a Pentax Asahi lens 50mm

Hi, I have a (manual) Pentax Asahi lens 50mm on my 7D. I've tried it many times and it does look like to have front focus problem. How can this problem be fixed?

(I hope this is the right forum. If not, please tell me where I should post this. Thanks!)

Are you focusing looking through the viewfinder? If the image is in focus on the focusing screen, ie what you are looking at through the viewfinder but the result is front focused it's possible the focusing screen or something else needs to be adjusted. This problem would occur for any lens mounted to the camera though.

Try focusing using live view. If that solves the problem it shows that something in the path to the viewfinder (probably the focusing screen) needs to be adjusted (moved).
When using Live view to focus the result has to be good so really that test is just confirming you are actually seeing front focusing.
Being a manual focusing lens, the problem can only be the camera.

Thank you for your reply, Dave! Yes, I use the viewfinder. The problem seems to be just for this manual lens. My autofocus Canon lenses are doing fine. I'll try focusing with live view and see what happens.