Not having ever had one, I just got a 135 optar in the SS shutter. I have two questons; what is the "O" setting on the shutter for? It does not quite behave like "T", whose position on the shutter scale it holds. Also, does the lens hood/cocking grip unscrew to insert filters? Mine is tight and I do not want to force it.

I have not seen the 1000 shutter for many, many years, but if memory serves, "O" (for Open) is a press-focus control, allowing you to open and close the blades to focus and compose on the groundglass without having to set the shutter to "T," tension it and release it, etc.

The hood is said to unscrew, allowing a Series 6 filter to be dropped in. This seems to be done by turning it in the opposite direction from the tensioning direction.

There has been a good deal of very recent discussion of that shutter on this site, and you might want to look it up. The sense is that the shutter is a fine performer if you treat it with great care, and the writers say what kind of care is needed.