Kaiser 40mm Push-On Lens Cap

I don't know about Pentax lenses. I use it to cover my Leica 50mm Summicron and my 135mm Elmar lenses. Both have 39 mm B&W clear filters attached. The caps fit nicely over the filters that have a 40mm OD but a 39mm threat. The caps fit on both lenses and, therefore, should cover any lens that has a similar outside diameter.

This Kaiser 40mm Push-On Lens Cap is not compatible with the Rollei 35S.

Kaiser makes a 82mm Tiffen 82mm variable ND filter version for use with 82mm filters.

No

I really like these lens covers, as an alternative to push-on caps:OP/TECH USA Hood Hat, SmallB&H # OPHHS35B Mfr # 8001112This will be the correct size for a 77mm.

If the focal length is 80mm, it doesn't mean the cap/filter size is 80mm. It depends on which version of 80mm lens it is. Typically a push on lens cap should be about 2-3mm larger than that of the filter size. For example is the lens has a 77mm filter thread, a 80mm push on cap should work. The older Hassy lenses took Bay 60 filters, that would be about 60mm in diameter , so a 63mm push on cap would probably work.

Yes - I use these85mm caps on 82mm step up rings and also on a few lenses with 82mm filter threads.

I completely concur with Gaston. The best way is to measure the rear mount and even then i would order multiple sizes just to make sure you get the correct one and then just return the others that do not fit perfectly.