Free: Contests & Raffles.
If you have fogging on the outside there are a couple of things you can do.... Keep your binoculars/spotting scope/rifle/range finder, etc., inside your vehicle at night, don't bring them into a tent or trailer. They will warm up inside and when you go outside the temp difference will allow them to fog. You want to keep them the same temp as the outside air if possible. When you are looking through your binoculars or spotting scope, breath out of you mouth and breath down, away from your lenses. This will keep the condensation from collecting on your lenses. I try to hold my breath when it is important. Sometimes I like to keep my eyes a ways back from the lenses, the heat from your eyes can make them fog.Don't use any scope caps (like the Butler Creek ones) on your scope, there will be a temp difference between the outside air and the air trapped in the scope cover. When you flip open the scope cap, the scope will fog. Don't use scope caps. Next to last, I keep a paper towel in each pocket that I have to wipe the lenses in the rain, fog, etc.Last, use your finger when you need to.
This is what I've been using because the technicians at Leupold suggested it. The more you apply it, the better it works. I clean my optics at the end of every day and re-apply this stuff and have had great luck. I try to wipe the glass as little as possible in the field and keep it uncovered throughout the day.http://www.kleervu.com/shop/2oz-anti-fog-cleaner/
Do not use paper towels to wipe any quality optics.I won't even use them on sunglasses.Get a lenspen that has a brush on one end to remove dust (eastern WA volcanic soil is actually fine grit and does a great job of scratching glass surfaces) and carry a microfiber wipe (many sunglasses include a microfiber bag to be used as a wipe).If you invest in good glass, take proper care of it.