Modify a Canon EOS-300 into a manual M42 mount camera!

Step 2 Take out the original focusing screen!

It is pretty easy if you have the right tools. All you need is a long screw driver with a sharp-pointed tip. If you look closely, behind the mirror padding you'll see a metal notch that you can insert the pointed tip in. Carefully pry the metal notch towards inside the camera, and pull it up. The thin metal frame will come out easily. Then carefully take the original focusing screen and brass spacer out. If you want to use the focusing screen in future, pay attention to not scratching/greasing it. It is made of plastic and virtually impossible to clean.

Look at the photos below for the step-by-step disassembly process.