You didn't describe exactly how you made the pinhole, the actual mechanics may affect the quality. The method described here has produced the best results for me. I have used #600 grit wet-or-dry sandpaper wet, with gentle pressure and circular motion to do the sanding. My last one was blackened with a liquid used in making brass model railroad parts (some sort of sulfide chemical).
Ok, I cut out a square from can..than i grinded it and make a hole on my first attempt.
Thanks for link, I will try it