astromania flexible dew shield for telescope front outer diameter from 100-123mm diameter - keep dew away and gives you clear observing for the entire night astromania a dew shield is an essential accessory that protects your optical tube from excess moisture forming condensation on the corrector lens. a lens shade also helps block out stray light outside the path of the telescope for better viewing and astroimaging.astromania dew shield keeps dew away and gives you clear observing for the entire night and protect your optics from dew and stray light.in clear nights, dew is often a real problem. after only a few hours, the optics start fogging, making observations or photography impossible. a good dew shield reduces the risk of fogging and extends the observing time. on the inside, dew shields from astromania optics are coated with felt which absorbs dew. dew can be a problem at almost any time of the year. especially when it's a little cooler, tiny droplets condense out from the water vapour in the air and fog-up the optics of your telescope.the astromania dew shield keeps dew away and gives you clear observing for the entire night. details: suitable for tubes: diameter from 100 mm to 123 mm material: abs contact surface to the telescope: foam rubber inner liner: black felt - light and dew absorbing height of the dew shield: 180mm total lenght: 435mm