I wanted to offer you a simple technique for focusing your Enlarger's Lens. (I had originally developed this for my 8mm Projector Lens.) This method is essentially perfect, and it doesn't require using the Negative. All you need to do is use a Strip of Aluminum Foil -- just fold it over three layers thick for strength to the 35mm or 60mm width of the Film Strip. Using a sharp Razor Knife, softly cut two finite vertical Slits about 1cm long near the center. You then simply use the tiny amount of light which passes through the Slits to focus the Lens. This focus will be perfect, and is much easier and quicker than using an image on Film which itself could be out of proper focus. Cheers.