On some telescopes (refractor, ED-APO...) the dew cap does not hold firmly enough and slides down when observing near the zenith.

On some telescopes (refractors, ED-APOs, etc.), the dew cap doesn't hold firmly enough and slides down when observing near the zenith.

In these cases, the velour applied to the edge of the lens cell can usually be reinforced (doubled up) with adhesive tape (duty tape or fabric tape).

To do this, the dew cap must be removed. This is almost always accomplished by unscrewing an aperture ring or similar device. Often, just a piece of adhesive tape is sufficient, and it doesn't always have to be completely wrapped around the lens.

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