I recently read a thread on another site about the Teslong bore scope available on Amazon for the princely sum of $49.99. It was getting rave reviews from people who had used 1. Well, I had some points to burn so Amazon got them and I got a cheap borescope. It DOES NOT have a viewer, it need to be viewed on a laptop, Ipad or smart phone. Very simple to use and instructions for mant different devices. Basically plug it into a USB port and open up the camera. I was amazed last might as I used it on a used barrel, the clarity is amazing for $50. Very nice addition that I really didn't need but now I will be able check throats. Also checked my crown inside out. Picks up the tiniest piece of patch lint. The focal point is definitely correct.