for instance, i have gone to using figures at 200 percent size, because it gives dynamic cloth more room to breathe.  but of course, a 50 mm focal lenght isn't the same when the char is twice the size, so i'm wondering if someone knows a way, or chart or something to convert focal length for different sizes.

doubling the focal length hasn't worked, but i didn't expect it to.  so far i've been running around 70 or 80, but still doesn't look right.

i'm trying to shoot at the same length that the human eye sees at, roughly 50 mm.

How about pulling everything back down to 100% after you run the cloth sim? That side-steps the whole issue.

However, if you insist...

Set your camera for the scene at 100%

Rescale everything to 200%

Use focal length to change the camera viewpoint until it looks like it did at 100%.

That's about as close as I think you're going to get.

I wouldn't change the focal length at all.  Use the Dolly controls to reposition the camera.  Changing the focal length will give at one extreme a fish eye look and at the other a flattened out look.  Of course, if that's what you are after, go for it but IMO, dollying the camera is the way to go.

Here's no.3 and no.4

Scale the camera to 200% as well. You may have to adjust Dolly-Y, but that's it.
You should not note any distortion or change in perspective.

Finally, you may try adjusting "Focal Perspective" to compensate for the larger scale.
Leave Focal Length at say 50, reduce Focal Perspective to 25-30.

I just tested your option 3. Works like a charm!

(Who'd have thought they put that "scale" adjustment on that camera for a REASON?)

ROFLMAO

fantastic guys thanks for the crazy fast response

i'm gonna try the scale camera one