If the lense is a very pricy one and the filter is a basic, low cost one as recommended for lense protection, it sounds like the filter has done its job and needs to be sacrificed. Maybe, though, resting the filter on a slab of dry ice while holding the lense in your hand could creat enough differential expansion and contraction to allow the parts to be unscrewed. Charles -------------- Original message -------------- > I'm not certain if this is off topic or not. If it is OT please excuse me. > > I've dropped a (Pentax 35mm) camera lens. With any luck the elements have > not been displaced and at any rate there is no cracking of them. However the > filter has deformed and will not now unscrew. WD40, Plus-gas or caustic soda > are obvious no-nos. Anyone any ideas? The thread is 40mm-ish by 1mm pitch & > both the lens and filter are some kind of light alloy. > > > MODEL ENGINEERING DISCUSSION LIST. > > To UNSUBSCRIBE from this list, send a blank email to, > modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject > line. MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.