A dog can see at 20 feet what a normal human can see clearly at 80 feet. In other words, the vision acuity (focus, sharpness) for a dog is worse than that of a human. An object that we can see clearly may appear to be blurred to a dog looking at it from the same distance.
Most all dogs, including the dachshund, have about 20:80 vision.
But they can ‘see’ better than us in other ways:
Dogs can detect motion better than humans can.
Dogs can see far better in dim light than we can.
When your dog recognizes you on sight, it is more likely because he recognizes your typical movements than that he actually recognizes your face!
Related: Can Your Dachshund See Color?