Hexanon 15mm fish-eye, how to change filter?

[Pontus]

I can't rotate the ring for changing between the built in filters on my Konica Hexanon UC 15mm fish-eye lens. Is there a special technique that I'm unaware of or is the ring simply stuck?

[Pontus]

Thanks Attila for the following information. There is a button on the filter ring that has to be pushed forward.

There are four filters built into the lens:
- SKY
- R60
- B8
- Y52

I wonder, can the lens be used in between, i.e. without a filter? It is technically possible (I checked on my copy) but is it optically sound? Some lenses (usually mirror lenses and long telephoto lenses) require the use of a rear filter for correct operation.

[Attila]

I think this lens is usable, try it out and we will know more