Oui, c'est compartible pour le 450D, car c'ests compatible pour tous les autres (40D, etc...)

Pour le foncitonnement, voici quelques détails...
Focusing “by eye” on a DSLR screen without manual focusing aids is very difficult. In manual focus mode, lenses designed for the camera can use the autofocus system’s viewfinder focus confirmation, but this does not work when using an adapter as the camera does not recognise the lens as part of the camera system. Focus confirmation device is designed to be permanently attached to an adapter and tells the camera to use its autofocus system to help confirm when the subject is in focus.

Focus confirmation device is a plastic plate with a group of contacts. When glued to the Lens, it reports focal distances and aperture to a camera. You can program any values. By default, the focal distance is 8 mm and the aperture ratio is 1:3.5.

Using an Focus confirmation device will give the same focus confirmation signals as with an autofocus Canon lens and all shots will show in their EXIF data that they were taken with a set focal length and aperture.

How it works:
1. Set the camera to "M" or "AV"
2. Focus on an object manually until the confirmation signal appears (this may require a half-press on the shutter release on some camera models).
3. Close the diaphragm on the lens to the required setting. In aperture priority mode the camera will calculate the shutter speed automatically.
4. Take your shot.