I found sometime the filter panel can detect camera model so I can select model for filtering, but sometime (meaning in another folder with photos from the same camera) the filter panel does not show camera model selection criteria. it is very strange.
I solved by myself. this is the behavior of Bridge: only when a folder has photos with more than 1 different camera model, the filter panel will display model selection for filtering.
Yes, you are correct. Here's another example: Let's say you have taken a folder's worth of images all in Portrait view. No options. But if you have any in Landscape view, you will have that as an option to filter on.
As long as there's an alternative option for anything to filter on, it will show up. Otherwise, there will not be an option in the Filter Panel.