Fish-eye Zenitar 16mm infinity focus readjustment ?

[edri]

I recently learned that the fish eye Zenitar 16mm lens provides better results for digital cameras without the rear clear filter. Because it is said that this filter is part of the optical path, after its removal it is necessary the readjustment of the infinity focus. How does this readjustment?

[visualopsins]

Down near the bottom of this page, in section "Rear filter needed?": http://www.4photos.de/camera-diy/Zenitar-16mm-Filter.html

The lens I had was already adjusted.

[edri]

Thanks. I understand how to readjust the focus. But how much should be rotated the ring? Is there a marked sign or readjustment is made through trial?

[ZoneV]

You have to try.

[edri]

I tried and the focus ring screws have not problems. The problem is with the screws from the hood, very small and stiff. Because I can not remove the hood the adjusting range for infinity focus is limited.
In addition, to the ring with the 3 screws there is a small metal piece that slides into a ditch (I do not know the mechanical technical names in English ). Even if I can change the position of the hood, the assembly the metal piece+groove will limit the focus adjustment. That's it. Now the focus index overlaps with the infinity sign. I would have liked to overcome the infinity sign, towards the letter M in my version of Zenitar (PK mount), but from previous reasons I can not.
Anyway with rear filter mounted it is better than no filter and infinity focus without readjustment. I noticed now that if the filter is screwed back not very tight and it is left very little toward the back of the lens, the pictures appear surprisingly clear.

[visualopsins]

Ditch is fine. May also be called a slot.

The focus needs to be adjusted so the rear surface of the rear element of the lens moves to the same position as the rear surface of the filter -- a distance of few mm. After hood is removed there should be enough adjustment, before metal piece in ditch hits end of ditch.