Improving Barlow Lens Performance
Some inexpensive Barlow lenses degrade the image by throwing glare into the field of view. The problem stems from the fact that they are not adequately baffled to deter internal reflections. But you can improve the situation:
1) Blacken the edges of the Barlow lenses with a Testors flat black paint pen or a black "Sharpie" permanent marker pen. If you get fingerprints on the Barlow lenses in the process, just clean up using a safe lens cleaning technique - fresh Q-tips and your favorite lens cleaning solution (Windex, isopropyl, etc.).
2) Apply a strip of flocked paper or very fine sandpaper painted flat black to the inside circumference of the barrel holding the Barlow starting just below the point where the eyepiece barrel stops when it is fully inserted.Published in the May 2001 issue of the NightTimes