I have a Celestron EdgeHD 8. I live in the Portland, Oregon area. I have an AP location in my backyard where I use the EdgeHD. I have significant problems with dew. Currently I have, and use, the Flexi-Heat Dew Shield. It works, but it has a tendency to sag, and cause some vignetting problems. I am considering the Astrozap aluminum dew shield, but it is very expensive, and I wonder if it is worth it? And I wonder why it is not heated? I would think that once the shield cools off it would not be of any benefit. I could put some heating elements on it, and it would seem that the aluminum would spread the heat all around the front of the scope. But since the product is not shipped with heating elements, there must be some reason why this is not done. Can anybody explain this to me?