Well, first let me say that as to "would this have helped", it really depends on the degree of moisture in the air. If it's really
humid out, then a dew shield won't really help for too long. As I said, I do a lot of my telescope viewing near a small lake at Findley State Park about 20 miles south of my house. The area where I usually set up is literally on the dam, right next to the lake. Some nights the dew and moisture isn't too bad at all and the dew sheild makes all the difference in the world. I have had nights though, especially when it's really hot and humid in mid-summer or really cold in the middle of winter where it really doesn't help much and I end up spending a lot of time with a soft cloth wiping the condensation off my telescope and camera. Usually nights like this, everything gets pretty soaked anyways and I'm not really sure there's too much of anything you can really do about it (other than maybe building a nice, hot bon fire! LOL!). Like I said, it really just depends on how moist the air actually is.
Now as to the "how to", it's really simple. If you're using a camera lens for example, a 1 liter pop bottle will probably work...depending on the diameter of the lens of course. If it's a larger lens, you may need to use a larger bottle. In the case of my 5" Orion telescope, again I use a 2 liter bottle. Basically, just cut both ends off the bottle, cut a slit right up the middle, wrap it around your lens and secure it with a piece of tape...that's pretty much it. If you want to get really fancy, you can even spray paint the bottle flat black so you don't get any weird reflections! LOL!!!
Here's a link to the Orion dew shield to give you a better idea of what I'm talking about...the priciple is the same.
http://www.telescope.com/control/produc ... t_id=A0031
Now I would like to add that while I've never tried this with a camera lens, for telescopes they also make these things called "dew zappers". Basically it's a little strap that wraps around the lens and is powered by a 12 volt power source (like a car lighter or a portable battery pack). It heats the lens a little bit to keep it above the dew point. Again I've never used one on a camera, but on telescopes I can say that they work like a miracle! I've attended a few Star Partys where guys use these things in the dead of winter and even on the larger telescopes, they don't get any condensation at all. Having to have a power chord and a battery or something would of course limit your movement with a camera, but if you're planning on being stationary...say taking pics of a sunset or your meteor shower on a tripod for example, than I wouldn't see that as being a huge problem. Again, here's a link...
http://www.telescope.com/control/produc ... t_id=A0030
I guess as long as I'm at it, I should also mention this handy little device...
http://www.telescope.com/control/produc ... t_id=05601
As you guessed by the picture, basically it's a low power hair dryer that plugs into your car's lighter socket! LOL!!! If you get dew forming on the lens, just run back to the car and "blow dry" it! LOL!!!
Alrighty, I hope this helps!