Shutter Speed vs Aperture
 

I understand that filming at around 1/50 is ideal (there are certain variations for certain things but lets say I'm shooting 24fps).

The slower shutter speed causes the correct amount of motion blur that allows things to look "the best". However, by cranking up the shutter speed to about 1/1000 this allows a shallower depth of field.

You can't add dof in post, but you can add motion blur. I've been messing around with FCP's motion blur filter to footage shot at 1/1000 however I can't get it just right.

Has anyone ever tried this? or is there a reason why no one has?

Any advice is greatly appreciated.

Of course the shutter speed isn't related to DoF itself; it's just that a faster shutter speed forces a wider iris, which is what makes for the shallow DoF.

A better way to do this is with using ND filters to force the iris more open and leave the shutter at 1/60 (or 1/50 in PAL-Land).

I'm not familiar with FCP's filter, but I would guess that it adds blur to the whole frame. I think it would look un-natural for the whole frame to be blurred if only certain parts of it are moving.

Adding motion blur in post has never looked quite right to me. I second Adam in the ND recomendation - and also that shutter speed has no direct affect on depth of field. 1/48 is only necessarily "ideal" when shooting in 24p if you want the 180 degree look.

Yeah, I understand that that shutter speed doesn't directly correspond with DoF but it does directly relate to aperture which in return directly relates to DoF.

I agree that ND filters are the way to go, the only problem is that shooting with old legacy lenses on a GH1 I come across the problem that my lenses have different filter sizes so I'm going to need to spend a bunch of lenses on ND filters.

I've come to the conclusion that FCP's motion blur filter is utterly useless and looks like crap. Maybe it's time to look into Motion of AE.

+1 for the ND!
The motion blur by itself takes you nowhere. The only post process that may work as some faked shallow DOF implies the use of mattes/garbage masks over a multilayered composition of the same shot and playing with blurs. The trick is that the shots should be framed carefully for this purpose.
Better to get the real shallow focus through the camera.

My 2 cents: any faster than 1/125th shutter looks like an effect to me (DELIBERATE strobing - best example: Olympic swimming for slo-mo's)

I've used 1/250th for talking head stand ups in television news in combination with lowered gain (-3dB), 6 stops of ND, telephoto focal length plus lens doubler/extender (robs another 1-ish stop) in order to get RAZOR thin DoF on 2/3" broadcast cameras when we NEEDED the background out of focus. I don't recommend shutter over 1/125th for "normal" shooting.

I'd get a matte box or filter holding system that allows you to fit filters of the same size. Some are some clip on types, although you need do adapter rings to fit different lens, but these are cheaper than filters. Otherwise you'll need support rods.

The professional systems usually involve square or rectangular filters (the filter sizes seem to be getting larger - nothing less than 4 x 4 on the pro matte boxes), you may get away with 3" x 3", but you'd need to check your lenses for vignetting.