UV/Clear Filter for Caltar II-N 360mm?

I just purchased a Rodenstock/Caltar II-N 360mm for my 8X10. It's truly a monster. Three and a half pounds! It came without a front filter, UV or clear. It looks like the thread is c. 100mm (4 inches). B&H lists a number of filters in that size range, but I don't know the correct one. Does anyone have the correct thread size for this beast? Thanks! Al

It might be a standard 105 mm thread. That's what my old Rodenstock spec sheet states, if your Caltar II is indeed just a relabeled Sironar-N, as they usually were. Be certain in advance what you truly need - colorless, UV, or skylkght, because they produce slightly different results, especially with color film; and also because anything new won't be cheap! Someone who has buys up unsold inventories of unusual filters and sells them at a discount is filterfind.net. Just hit the 105mm filter column and several of the kind you need are listed.

hopefully its not 100mm as they're a PIA to find. My Pentax 55mm ƒ3.5 has 100mm thread, and I couldn't find filters, so I had toget a 100->105 step up ring (which itself was expensive and special order.)

I checked both Rodenstock and Calumets own list. It's 105 mm in both.