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Tubes article
What is happening is that the lens is being prevented from seating
properly onto the tubes mount.
It is kept a little high by the small grub screw.
This screw doesn't do very much , it just prevents the tubes locking
ring from unscrewing and falling off when not used. (unlikely anyway)
It also keeps the mount ring in a position that is near correct for
immediate fitment of a lens , handy if used in low light situations.
(not often)
As you can see by the picture , on this one the screw is above the
mount seat by well over 1/2 of its diameter.
In an attempt to mount a lens , it will sit proud by almost 1mm on this
side and the mounts retainer ring will hit the tab on the lens and not
turn any further.
On some tubes the ring will turn a little bit more and it will hold the
lens down but ¨Don't¨ try this.
The lens needs to be mounted securely with a good turn of the locking
ring.
Dont risk a dropped lens !
The fix ? - Simply
remove the screw :-D
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