Rob,
The 28mm f3.5 lens had an accessory metal hood.
The 28mm f 2.8 came with a rubber hood. At least the 28mm f2.8 that I bought new in 1985 had one included in the package.
Both of the slower lenses used screw on hoods, and I would think that they could be used interchangeably.
I believe that you are right that the 28mm f2.0 had a different hood (even though it also has 49mm filter threads).
Well the lens hood should arrive in the beginning of next week.
If someone could kind enough to post the outer diameter and height of the lens hood of a 28mm 2.0 then I can compare it with the 28mm 3.5 diameter and height. Because I have the feeling the might be the same, except for the fancy writing on the side of the hood.
Happen to have all three. They are slightly different in diameter. The 3.5 and 2.0 are metal the 2.8 is rubber. The diameter of the rubber shade is misleading as it is thicker walled than the metal hoods. They are all the same depth. Just received the 2.0 with in the last week and a 28mm f2.0 lens to go with it. Whether the different diameters would make a difference on the lenses I am not sure. But the 2.0 hood is significantly wider so my guess would be that trying a 3.5 hood on the 2.0 lens might cause a little vignetting. Would it be noticeable? Won't guess. Anyone have thoughts on how to best test?