Schneider Kreuznach Optivaron filters

[7OSE9]

I have to buy a 80a filter and maybe a yellow and red filters for Schneider Kreuznach Optivaron 1,8/6-66 mm of my Beaulieu 4008 ZM II. What is the diameter required for the filters to be put in the "filter holder"? The manual says 8.5 series, but are difficult to find as this name.
Instead, if I wanted to mount filters directly onto the lens, which diameter filters are required for Schneider Kreuznach Optivaron 1,8/6-66 mm?
And which of the two solutions is preferable?
Thank you.

[sciolist]

I've fit 72mm filters into the lens hood compartment designed to accommodate series 8.5 filters. The front filter attachment size of the lens is 62mm, but it's best to use the compartment in the lens hood because of the risk of vignetting when that lens hood is attached to a filter.

[7OSE9]

Sciolist,
have you noticed that in addition to put filters in the filter holder and with screw directly on the lens (vignetting risk) can be screwed in FRONT of the filter holder? Serve 77mm diameter filters, I already have some of Krasnogork 3 of that size, I might try this method. What do you think?
Practically, 77mm is the diameter of the lens hood; then, it should be screwed over the filter.

[sciolist]

Sciolist,
have you noticed that in addition to put filters in the filter holder and with screw directly on the lens (vignetting risk) can be screwed in FRONT of the filter holder? Serve 77mm diameter filters, I already have some of Krasnogork 3 of that size, I might try this method. What do you think?
Practically, 77mm is the diameter of the lens hood; then, it should be screwed over the filter.

This is scarcely different than screwing the filters directly to the lens; the risk of vignetting is the same or worse.

[7OSE9]

You mean for the distance of about a centimeter that there would be between the lens and the filter? I had not thought... ops!

You have 72mm because because the next step of classic filter diameter is the jump to 77mm, and instead the series 8.5 (74,8mm) is more difficult to find? In fact I found almost nothing of 8.5 series...
With 72mm i have no risk for vignetting? The filter holder contains 77mm well even if it is originally made for more larger filters?

Thank you.