I managed to find the Rollei IR filter in bayonet 1 size for my Rolleicord. It was new and came from Mr Cad in Croydon England. It was expensive( about 50GBP). It is quite opaque, like an IR720 and gives good results with the Rollei film. I have heard that it is "focus-corrected" but I have never seen this in any Rollei publication. I have used it for landscape, and therefore have not seen the effect with the lens at large apertures. The shots I have are in focus without making any adjustment. In many ways the TLR is the ideal IR camera as you can work with the filter in place and see to compose/focus.