Macro Focus - Land vs. Underwater

On land my 4040 macro focus range is rated at 8 inches to 2.6 feet. What will that be underwater with a flat port?

Well this is what I think the answer is, I willing to be proved wrong by someone who actually knows:

If the port window was right next to the lens, and it was a thin lens, then the minimum focal distance would be increased by a factor of 1.33 (ie the refractive index of sea water).

So this would mean that the 8 inches goes to 10.6 inches. In reality the port is not right next to the lens and it isn't a thin lens so this factor is reduced.

I guess I'm going to have to spend this evening with a camera in bucket of water to test.....

I've been waiting to see if someone else would answer this since I'm not certain either. I believe nicholasmo is correct, though. The distances should be increased by a factor of 4/3 ignoring the internal distance from the lens to the port. Actual focusing range of the camera and DOF may overwhealm the difference though.

I would have thought that focal length decreases due refraction causing magnification. I think I'm right about that, but I'm not sure.

Perhaps it's 8/1.33 = 6 inch ?

The math and factor of 1.33 may be wrong but someone should be able to verify from experience if minimum focal length increases or decreases u/w.