The Idiot's Guide To Aspect Ratio's
 

It may have been mentioned here before, but, can someone please give me the Idiot's Guide To Aspect Ratios (e.g. 1.85:1).

Craig Syverson has a video podcast that he never updates (hint, hint to Craig) called Videogrunt at:
http://gruntmedia.com/videogrunt_directory.html

Since there are only five of them (hint hint to Craig), and they are only about 4 minutes long, it won't take you long to watch them all. Episodes 2, 3, 4, & 5 are all basically about aspect ratio, letterboxing and pan & scan.

Unfortunately Craig never did one on pixel aspect ratio like he said he would (hint, hint, Craig), but screen/picture aspect ratio is very elegantly covered there.

Pixel aspect ratio is a different beast than aspect ratio, and can occasionally bite you in the butt when editing video. If you are on a quest to learn about aspect ratio, make sure you also gain an understanding of pixel aspect ratio.

hey, don't be intimidated. It's like learning to ride abicycle. Once you get it, you never forget it.

The aspect ratio number is just a ratio between height and width, or vice-versa. Film keeps the vertical height to a value of 1, so the horizontal units can be in fractions, whereas Video keeps the ratio in whole numbers.

Hence 4x3 (video) is the same ratio as 1.33 : 1 (divide 4 by 3 and you get 1.33). 16x9 video is the same ratio as 1.777777... : 1 (1.78 : 1).

Some film aspect ratios over the years:
4-perf 35mm Full Aperture (Silent Era & Super-35): 1.33 : 1
4-perf 35mm Sound Aperture (Academy): 1.37 : 1
4-perf 35mm Matted Widescreen: various -- can be matted (using a projector mask) to 1.85, 1.75, 1.66 but 1.85 is the most common
4-perf 35mm Anamorphic Widescreen (CinemaScope): when the image with a 2X horizontal squeeze is stretched back out to look normal, the current shape is 2.39 : 1 (rounded up to 2.40 by some people) but it used to be 2.35 and this is still a common term.
3-perf 35mm Full Aperture: 1.78 : 1
Super-16 Full Aperture: 1.68 : 1

Many formats involve cropping Full Aperture (the maximum possible area that can be exposed on the negative) to different aspect ratios. Super-16, for example, may have a 1.68 : 1 negative but it is often trimmed a little to 1.78 : 1 for transfer to full-frame 16x9 HD, or blown-up to 4-perf 35mm for projecting with a 1.85 projector mask.

GLG...

Maybe this will help

Thanks everyone. Scott, that website was just what I needed.

Don't you wish Craig would make some more?? Until I saw videogrunt, I had no idea Thomas Edison and George Eastman conspired to make my iPod Video screen 4:3.

Yeah Craig, make some more!!!

American Cinematographers Manual goes into each format extensively.