I just read the Human Interface Guidelines for Search Patterns. It does not define any shortcut for focusing the static filter.

I suggest to set it to "Focus the input on alt+I (localization dependent) and on ctrl+I." like it does for the dynamic filter. Because both should not be available in a single dialog — so they should not interfere. But they do the same from a users point of view so using the same shortcut natural and intuitive.

"Static" filter should be visible by default. The major purpose to use them is for very long lists, like countries in case of regional settings. Therefore we wrote "Do not apply a short-cut to open or close the input. Consider to have an option in the menu under 'view' or the configuration." (at section Static Filter). The dynamic filter instead should apply you suggested ctrl+I short-cut which toggles its visiblity "Show the filter input on short-cut ctrl+I." (below Dynamic Filter).

PS: I should read postings carefully, sorry. You talk about focusing. That should be done via the control label. The example below has a static filter with the caption Fil&ter so you press alt+t to focus the input. Since the dynamic filter bar has no caption it needs a different method. That's the idea with "focus on ctrl+I" there.

I discussed the issue with colomar. Since dynamic and static filter shouldn't be used simultaneously, the solution could be: "If you have only the static filter on the form, apply ctrl+I to focus the input. If the dynamic filter is available as well, add a caption with a hotkey for access."

My concerns are the double-use of a shortcut (I have to admit that both functions are closely related) and that the short-cut is not obvious to users (in case of the dynamic filter, ctrl+I opens and focus it). On the pro side is colomar's design argument: it looks weird and unbreeze to have a caption left of the input, at least for small applications like the legacy Kickoff.