This is so frustrating. I have a 16:9 project with a Raster Dimension of 1920x1080.

If I add on a video track the effect Film--> 1.66 Mask I get a mask that cuts from top and bottom.

But if instead I use from the Format tab--> Mask Margins--> the Mask margins preset --> 1.66:1 , I will get a left and right cut.

Check screenshots.

Why is this different?

The Film Masks in the Effects Palette were named for how they work in 4x3 SD video (e.g. PAL 0.8x576=460.8, and 460.8/768=1.66667 or NTSC 0.8x480=384 and 640/384=1.66667), so unfortunately they are completely wrong when applied to 16x9 HD sources. They are essentially legacy effects. You can still use them but will have to figure out how to manually modify them to be useful.

1.66 in HD would be 1792.8 pixels wide, so the _horizontal_ crop would need to be 0.93375.

1.85 in HD would be 1037.83 pixels high, so the _vertical_ crop would need to be 0.96096.

Classic 2.35 in HD would be 817.02 pixels high, so the vertical crop would need to be 0.7565.

Modern 2.39:1 in HD would be 803.34 pixels high, so the vertical crop would need to be 0.7438.

Job ter Burg:

The Film Masks in the Effects Palette were named for how they work in 4x3 SD video (e.g. PAL 0.8x576=460.8, and 460.8/768=1.66667 or NTSC 0.8x480=384 and 640/384=1.66667), so unfortunately they are completely wrong when applied to 16x9 HD sources. They are essentially legacy effects. You can still use them but will have to figure out how to manually modify them to be useful.

Oh, that makes so much more sense now!! Thank you so much for clarifying! But since I have to manually correct them to 16:9 sources another question comes in mind:

Should I still use the Film Effect or is there a better workflow to create those masks? 

I'm not sure if the target Masks from the Project Format are actually rendered in the export.

Target Mask can be apllied during export, either classic QT export as well as in the newer UME exports (MXF or MOV).

The old Masks can still be useful if you need to mask something and then add burnins on top of the masks. You just need to manually correct its X and Y size settings. You can also save a bunch of them to a bin.

Job ter Burg:

Target Mask can be apllied during export, either classic QT export as well as in the newer UME exports (MXF or MOV).

I tried exporting but the Target Mask is not applied.  I can see the Target Mask in the Format tab and also on my Monitor window. Maybe there is a setting I have to check?

It's a tick box in the MOV and MXF export settings, as well as in old-style QT export settings. "Enable Mask Margins".

http://community.avid.com/cfs-filesystemfile.ashx/__key/CommunityServer.Components.PostAttachments/00.00.89.42.49/Screen-Shot-2020_2D00_05_2D00_22-at-8.58.41-AM.png