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The length of the tube varies proportionally to the number of stars counted. If the length of the tube increases the number of stars we are counting will also increase.
There are so many stars in the galaxy that it is hard to count them with the naked eye. Human eye is a somewhat imprecise instrument. Few people have 20/20 vision without the aid of lenses, and the eye changes in light gathering capability and acuity with age. Another reason for this difference could be the weather; for example if it is particularly cloudy, fewer stars would be visible to us. Because of these differences, the numbers of stars that are visible to the naked eye are different from the ones present in the galaxy.
However, if we go to a very dark place our results will differ. In this case we will be able to view more stars in the sky than under normal conditions. This is because stars are known to be celestial objects; the visibility of these objects is affected by light pollution. Outdoor lighting tends to scatter light upward, brightening the background of space. This increases sky brightness and reduces the contrast between the background and fainter stars, until the point where they become invisible to the eye. Pollutants in the atmosphere can substantially increase the extinction of light as it is transmitted through the atmosphere which reduces the visibility of the stars. If we are in a dark place such as a wild area, there will be less light pollution; hence more stars will be visible to us.
Read more: How to think star visibility would change if you were to go somewhere very dark?