Taken from this post: http://www.fredmiranda.com/forum/topic/402782

Posted by Shirozina: "Here is a rough guide to adjusting the 50mm 1.7 MM and 28mm 2.8MM if they fail to reach infinity with your adapter.
50mm - remove the rubber focus grip and slightly loosen the 3 x head screws - this releases the clamping action of a semi circular ring inside the lens which locks onto the focusing helical. Slide the now loose focusing ring slightly away from infinity and then slightly squeeze it to grip the helical and focus back on infinity. It should only need a slight movement of a couple of MM at most. CAUTION! if you undo the screws to much they will disengage with the inner ring and you will have to remove the front assembly thus: Using the proper friction tool or ( as I did ) a small roll of electricians tape unscrew the lens ring ( the one with the serial number on). You will need to apply a bit of force to get the required friction. The roll of tape is good as the sides are sticky and the center is open so as not to touch the lens. Under this are 3 screws which when removed give access to the clamping ring. CAUTION! this also holds the front element in place so keep the lens upright!
28mm - simply unscrew the front of the lens beyond the focusing ring - it comes off in one piece together with the lens ring. You can also use the 'electricians tape' method as with the 50mm. Down the side of the inner lens barrel are 3 screws which hold a clamping ring - loosen these and adjust in the same way.
I use an angle finder-C to set the lens up and then check 100% blowups on screen at max aperture. Previous to my adjustment both lenses were focusing a little short of infinity ( Not realy noticable through the VF even with the angle finder) but obvious at 100% on screen - whan properly adjusted landscape images 'snap' into focus that even stopping down coud not compensate for previously."

I hope this isn't a repost.