Depending on the size of the camera/lens combination you might try a large zip-lock bag before you bring it in. Also, if you have a lens cover, put it on while still outside. What both of these methods do is keep the warm air off of the lens until the lens warms up to the inside temperature. Anything to keep the air off of the lens. If you use a clear filter (which also protects your lens glass from damage), the fog is on the filter and not on the lens glass.
Actually, the reverse has been more of a "problem" for me, i.e. if I am driving with the air conditioning on and see something. If you stick the lens out the window or get out on a humid morning, the lens quickly fogs up and you're out of luck. No photo !!!
There isn't much you can do except expose it to the air you will be shooting in for several minutes before your planned event. Going from an air conditioned room to a tropical environment will fog a lens quicker than anything and vice versa. A video camera is even worse because if the lens clears the internals may not. You may have to replace the tape too to get it to work again (that happened to me in Cancun).
I guess you could search for some anti-fogging agents to spray on your lens but I'm not sure you would want to this.
Not exactly sure (Sony has some info on the subject but I doubt I could find it now) but I couldn't operate the tape. Then I remembered reading something in the manual about it but didn't have the manual with me. I swapped tapes and then it worked. Later on I could put the old tape back in and use it. That reminds me that if you have a camera bag then it is best to take the camera out of it so that it gets to the same temperature as the outdoors (or indoors). Take the lens cap off too so it reaches the same temp. Of course this only applies for sudden temperature swings.
How does the fog affect the internals?[/quote]
Electronics and water don't go well together so it is recommended to let the temperature normalize so that the condensation can dissipate before powering up. Even better is to keep the equipment in a Ziplock bag until the temperature normalized as linthicum suggested above so that the condensation doesn't even occur in the first place.