How to Prevent Telescope Dew with Flexible Dew Shields

Quick Answer

A flexible dew shield physically blocks radiating heat loss from your telescope’s corrector or lens, preventing dew from forming in the first place. Fit it before the session and keep it snug to the optical tube for best results.

How to Fit and Use a Flexible Dew Shield

1. Check the fit before dark: Confirm the shield’s diameter matches your telescope’s optical tube. For a Schmidt-Newtonian, measure the outer diameter at the front cell. For a Meade LightSwitch, look for a shield that specifies 178 mm outer diameter. A shield that is too loose will slide off; too tight may not fit over the cell. Always measure before buying—most dew shield listings state the exact tube diameter they fit.
2. Slide the shield over the front cell: Gently slide the flexible shield over the front of the optical tube, making sure it covers the corrector or lens completely. It should sit snugly but not be forced. For scopes with a side bar or finder, align any notch in the shield with that accessory. If the shield has a notch, rotate it to clear the side bar—do not bend the shield to force it.
3. Secure the shield in place: Most flexible shields rely on friction to stay put. Press evenly around the circumference to seat it. If it still slips, you can add a small strip of Velcro or a soft strap—but avoid anything that could scratch the tube. A loose shield is a dew risk: if it shifts, it exposes the glass to the sky.
4. Use a heater for long or humid sessions: If you are observing for more than a couple of hours or in high humidity, switch to a heated shield. The Flexi-Heat shield warms the air near the glass, which keeps it above the dew point. Plug it in and set the power to a low or medium setting—you only need enough heat to prevent condensation, not to warm the whole tube. If you see dew forming even with a passive shield, that is the signal to add heat.
5. Store the shield flat or rolled: After the session, remove the shield and let it dry completely before storing. Flexible shields can lay flat or roll up, which makes them easy to pack. Avoid folding them sharply, as creases can weaken the material over time. Dry storage prevents mold and keeps the felt lining effective.

Flexible Dew Shield Options

• AstroZap Flexible Telescope Dew Shield for 8" LXD75 or LXD55 Schmidt-Newtonian Telescopes - AZ101: The AstroZap Flexible Telescope Dew Shield for 8" LXD75 or LXD55 Schmidt-Newtonian telescopes is made of lightweight, durable black ABS plastic and is felt-lined inside to absorb moisture. The felt lining helps wick away early condensation, and the flexible material lays flat or rolls up for easy storage, so it is simple to carry and set up.

  

• AstroZap Flexi-Heat Telescope Dew Shield for 6" Meade Light Switch w/ Notch - AZ819: The AstroZap Flexi-Heat Dew Shield for 6" Meade LightSwitch is custom fitted for optical tubes with an outer diameter of 178 mm and has a notch cut out to accommodate a side bar. This heated shield actively prevents dew in humid conditions, and the notch ensures a proper fit on Meade LightSwitch scopes without interfering with accessories.