Ok Michel, here's the run down. I apologise up front, for this will be somewhat long winded. lol

Alright, I'll start with aspect ratio's followed by their respected formats. For the sake of this discussion, I'll stick with widescreen formats.

1.85 - Flat Widescreen
2.39 - 2:1 Anamorphic (Scope)
2.39 - Super35 (Scope)
2.39 - Techniscope
1.85 - 16mm
1.85 - Super16

1.85 - Flat Widescreen:
Very popular. Inefficient use of image area. Open-matte transfer of image fits televisions well. 1.66:1 in Europe.

Movie examples:
Good Will Hunting, As Good As It Gets, Saving Private Ryan, There's Something About Mary, Waterboy, The Truman Show

2.39 - 2:1 Anamorphic (Scope):
Uses a 2:1 horizontal squeeze in filming, and a 2:1 horizontal unsqueeze in projection. Very efficient use of image area. Does not translate well to television (44 percent image loss).

Movie examples:
Star Wars (all), October Sky, Blade, I Know What You Did Last Summer, I Still Know What You Did Last Summer, My Best Friend's Wedding

2.39 - Super35 (Scope):
Uses silent aperture in shooting. 2.39:1 slice extracted from source and printed in scope format on theatrical release prints, requiring the 2:1 horizontal unsqueeze in projection. Very inefficient use of image area of source. Open-matte transfer of source fits televisions well.

Movie examples:
Independence Day, Titanic (except underwater scenes), Austin Powers (I and II), The Matrix, Air Force One

2.39 - Techniscope:
Poor man's scope. Runs film at half speed, using only 2 perforations per frame instead of 4. Scope theatrical release prints are made by blowing up each frame by a factor of 2 in the vertical direction only, which fits the "scope" release format perfectly. Note that this format used the image area very efficiently, but only has half the vertical resolution of films shot in anamorphic scope format.

Movie examples: THX-1138, American Graffiti, underwater scenes in Titanic.

1.85 - 16mm:
In shooting, very similar to 35mm flat widescreen format, except on a smaller scale. A 1.85:1 area is extracted from the 1.33:1 image area of the 16mm film and is blown up to 35mm, resulting in a hard-matted 35mm flat widescreen print. Movies shot this way look very grainy.

Movie examples: Clerks

1.85 - Super16:
In shooting, the soundtrack area of the 16mm film is used for image, resulting in a 0.493" by 0.292" camera aperture (1.69:1 aspect ratio). This source image is blown up to 35mm and printed in the flat format, resulting in a hard-matted 1.69:1 flat print, which is run at 1.85:1 in theatres, of course. Movies shot this way look very grainy.

Movie examples: Chasing Amy, Leaving Las Vegas

Now these are all film aspect ratio's in relation to their respected formats. In terms of what we're talking about here, you'll want a 1.78 ratio, which is the ratio designated for HD, more and less. You'll sometimes here it refered to as 1.76, or at least I have anyways.

In todays world of ATV (Advanced Television Standards), it pretty much boils down to the following, for the most part.

If you are a film buff and want to watch movies at home that are in the same format that was shown on the big screen, consider this: movies made for cinema screens are filmed with an aspect ratio of between 1.85:1 and 2.4:1, and the director consciously uses the entire screen to tell you the story. So when a movie is re-packaged for television broadcast, various editing methods are used to try and make everything on the large movie screen fit onto a 1.33:1 TV. That means that 40-50% of the movie is affected.

Another way to get cinema-sized films onto a TV is using the Letterbox format. Most people have heard of this. Letterbox means that no editing was done to the film, but rather the way that the TV screen is manipulated to match the aspect ratio of the film. By adding a black area along the top and bottom of the screen, often referred to as "black bars," the TV screen is able to mimic the aspect ratio of the movie screen. While you don't necessarily miss out on any action, this is not always an ideal solution because on smaller TV sets, the narrow strip where the movie appears is even smaller, making it hard to see all the details. The bigger the TV screen, the less problematic the letterbox will be.

Perhaps the greatest thing about widescreens is that they mean an end to the need for action-eliminating edits. Since the aspect ratio is of widescreen is closer to that found in movie theaters, there is plenty of room for the whole picture. However, because the aspect ratios do not match exactly, there may still be black bars around the movie (making it either letterboxed or sideboxed or both), but they will be narrower and therefore won't affect the image area as greatly.

And since more and more people are buying widescreens either in the form of a front projector or a RPTV, producers are filming specifically for widescreen formats. That means that there is more widescreen content available than ever before. Since more and more TV stations are expected to be broadcasting digitally and the top digital format, HDTV, can supply an aspect ratio of 16:9, widescreen will soon be everywhere. It is likely we will see the ubiquitous 4:3 TV slowly replaced by widescreens, in fact, it's already begining to happen.

To filter through all this, or to sum things up (Thank God Huh ), the official aspect ratio for all HDTV programming is 16:9. That's the case whether you receive your HDTV signals via local over-the-air broadcasts, digital cable service, or satellite TV. Even if you don't currently receive HDTV, you've probably noticed that more and more non-HD versions of HDTV programs are being shown in widescreen, like "The Sopranos" and "The West Wing." Many DVD movies are optimized for display on 16:9 screens. The technical term for these DVDs is "anamorphic", but their packaging usually says "enhanced for 16x9 televisions" or "enhanced for widescreen televisions."

Nearly all current Hollywood movies are shot at aspect ratios that are even wider than 16:9 (1.78:1). The two most common formats are 1.85:1 and 2.35:1, as previously mentioned. A movie at 1.85:1 is close to a perfect fit for a 16:9 screen, and even a significantly wider 2.35:1 film matches up better with a 16:9 screen than a 4:3 screen.

At anyrate, I hope I've been able to shed some light on this subject for you. If nothing else, I hope I was able to help a little bit.