Use a cheap microscope to make it easy to focus using the ground glass of your old camera. Print out the hood, fit it on the end of your microscope and enjoy a bright magnified image of what your camera can see. Make sure you turn down the lights on the microscope when using. It's an easy print with no overhangs. I stuck some felt on the flange at the end to stop the hood from scratching the ground glass. Avoid the microscopes with 1000x magnification as they give only give you a very small area of the negative. I used a 500x one which works well.