unsharp mask

[Reg52]

If I open an image then Cntrl E then select unsharp mask, I have a split screen with one image being the one I have opened called the original on the left as I look at it and another with generally 2 levels of unsharp mask applied on the right as I look at it.
Across the bottom are four buttons Apply to original image , Undo, OK and Cancel.
So far so good!
If I press Apply to original image what is supposed to happen?
I assumed that the Original image would change to that of the right hand image but that does not appear to happen, what seems to happen is that the right hand image gains two more levels of U.mask and is generally rubbish.
If I press OK instead, nothing at all appears to happen apart from it going to a single screen.

I am using latest download version on a 32bit Win 7 machine.
Any thoughts or ideas or explanations of what is happening awaited, thanks.

[Mij]

Unfortunately,like several other filters, the preview image is pretty useless because it shows how the image would look if it was the size of the preview window, which it never is of course.

I find the best way of using these filters is to zoom the image to 100% magnification (Ctrl+H) and scroll to a typical area of the image before you select the filter. Try a setting and click Apply to original image. Ignore the Preview, wait for the original image to update and look at that instead. If it is too little you can press Apply to original image again and the effect is cumulative. If it is too much press Undo instead and try a smaller value.

You might get better results from downloading an Adobe 8bf filter instead and using that (Ctrl+K).
Jazzman, who posts on this forum, has written a free Unsharp mask 8bf filter that you can get here. It has both Radius and Strength settings and the added bonus is that he will probably give you a bit of free technical advice right here, if you need it.

[Reg52]

Many thanks for the info, I have looked at Jazzman's page and downloaded a couple of his filters to try.
Just got to work out how to get them to appear in IV, no time right now!