I have an Ektar f7.7 203mm On a Graphic View. The lens is very small diameter, about 33mm o.d., and I’m wondering if graduated filters will work on it. If not how big of a lens will I need, and give me a few examples. My current lens has no threads so I may have to make a bracket of some sort to attach the filter holder, that is if I can use GND filters with it at all.