Very nice! The image quality in #2 and #5 is excellent and #3 is a very dramatic shot! Are you using an EOS300D?

Can someone tell me whne the F-16 Falcon I have known since childhood became a 'Viper"?  

The name "Fighting Falcon"
The U.S. Air Force officially named the F-16 "Fighting Falcon" on July 21st, 1980, during a ceremony at Hill AFB in Utah (the home of the first F-16 unit). At the ceremony F-16A #79-0290 sported a special logo painted by Salt Lake City artists Matt and Mark Waki.
Four year earlier, in 1976, the Department of the Air Force had organized a "Name-the-Plane Contest" for the F-16 at MacDill AFB in Florida. The winning entry was submitted by TSgt. Joseph A. Kurdell, the Photo Sensor Shop Supervisor for the 1st TFW A&E sqn.

On 11 May 1976, TSgt. Kurdell received an official letter from the Department of the Air Force, congratulating him for submitting the prize-winning entry in the "Name-the-Plane Contest", winning him a free dinner at the MacDill NCO Mess.

TSgt. Joseph Kurdell explains where he got the inspiration for the name:

"Prior to being stationed at MacDill AFB, Tampa, Florida and after a short tour in Korea, I was teaching at the Photographic Engineering School at Lowery Air Force Base in Colorado.

Being in the vicinity of the Air Force Academy, my family and I used to visit there quite often especially during their football seasons. As you probably know the Falcon (the bird species) is the school mascot, so this is where I got the idea from when given the opportunity to name an aircraft. "

The name "Fighting Falcon" also helped distinguish the F-16 from the "Falcon" series of business jets from French manufacturer Dassault.

Viper: the unofficial nickname
The F-16 is often referred to as the "Viper", a nickname is especially popular with people involved with the F-16. Before "Fighting Falcon" was selected as official name, pilots at Hill AFB, the first F-16 base, came up with a number of proposals, inlcuding "Viper". Lt. Col. Pat "Gums" McAdoo, USAF Ret., one of the first F-16 pilots at Hill AFB, recalls the origin of the name "F-16 Viper":

At end of runway, the F-16 did resemble a cobra or something as it approached you. However, I think Northrop had already taken that name for the YF-17.

We all voted, and Viper came in really high. Seems there was a series on TV that had 'colonial Vipers' flying off of Battlestar Galactica (a term later used for the Eagle).

In any case, the Generals didn't want a plane 'named after some snake'!

Falcon was a good name, and it fit in with the motif that the Eagle had created. Sort of a little brother, but still a 'Bird of Prey'. In fact, GD had a great promo out in late 70's called "Bird of Prey", and it used the Falcon as the real world model.

Even when F-16 Fighting Falcon became the official name, Viper stuck around and became the unofficial nickname for the F-16. The name "Viper" is even officially used for the Joe Bill Dreyden "Semper Viper" award, which is awarded for excellent airmanship by F-16 pilots.

Official International names
Although "Fighting Falcon" has been adopted as the official name for the F-16 by many international customers, some airforces have indigenous names for (specific variants of) the F-16:
Netz: or 'Hawk' - used by the Israeli Air Force for its F-16A aircraft.
Barak: or 'Lightning' - used by the Israeli Air Force for its F-16C aircraft.
Brakeet: or 'Thunderbolt' - used by the Israeli Air Force for its F-16D aircraft.
Suefa: or 'Storm' - used by the Israeli Air Force for its F-16I aircraft. Sometimes spelled as Sufa.
KF-16: Designation used by the RoKAF to denote the South Korean produced F-16s. Note that this designation does not follow the US Tri-Service designation system. The 'K' simply stands for Korea in this particular case.

Other nicknames

Of course the F-16 is also known by a variety of other, less commonly used, nicknames:
Electric Jet: Obvious nickname for the first fly-by-wire aircraft.
Lawn Dart: caused by a higher number of mishaps experienced in the early years
Midnight Falcon: "Marketing" name used by General Dynamics/ Lockheed Martin for the F-16C to highlight its day/night all-weather capabilities.
Desert Falcon: "Marketing" name used by General Dynamics/ Lockheed Martin for the F-16 Block 60.