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#1 Jim Nelson

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Posted 12 August 2010 - 05:54 AM

Hi,

When we use a wider aspect ration (for example, we go from 4:3 to 1.85:1) does it mean that the image gets wider and taller? Or just wider?

What about when we you use bigger sensors/films? (For example, we go from 35mm film to 60mm film) Do we record more of the scene in terms of more width or in terms of more height? or both?


I've never quite understood this :(


Thanks for your help.

Edited by Jim Nelson, 12 August 2010 - 05:55 AM.

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#2 Brian Drysdale

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Posted 12 August 2010 - 06:44 AM

Check this:

http://en.wikipedia....t_ratio_(image)

A larger sensor will have more area, the aspect ratio used will depend on the one selected by the manufacturer. Usually both image width and height increase to maintain the aspect ratio. 35mm film can be used in various ways. http://en.wikipedia....wiki/35_mm_film As can 65mm (70mm projected) http://en.wikipedia....wiki/70_mm_film
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#3 Freya Black

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Posted 12 August 2010 - 01:37 PM

Hi,

When we use a wider aspect ration (for example, we go from 4:3 to 1.85:1) does it mean that the image gets wider and taller? Or just wider?

What about when we you use bigger sensors/films? (For example, we go from 35mm film to 60mm film) Do we record more of the scene in terms of more width or in terms of more height? or both?


I've never quite understood this :(


Thanks for your help.


The key word here is ratio.

It doesn't matter how big or small the image is, it's about the ratio of the height to the width.
You can record in standard definition in 16:9 or high definition in 16:9 but the ratio of height to width remains the same.

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#4 David Mullen ASC

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Posted 12 August 2010 - 10:11 PM

Yes, it's just a ratio of height to width, whether you want to think of a widescreen image as being shorter or wider than a square image is up to you.

Some movie theaters have a fixed screen height, so wider aspect ratios are wider on the screen, less common is to have a fixed width so that widescreen movies are shorter... other theaters split the difference, a 1.85 movie is slightly taller but less wide, a 2.35 movie is wider but slightly less tall.
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#5 Jim Nelson

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Posted 15 August 2010 - 06:29 PM

Thank so much. I'm sorry but I'm still a bit confused about going from say 16:9 to 2.39:1. In what way is the image changing?

I'm also still confused as to whether the image gets wider or taller or both when we use bigger sensors? :(
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#6 David Mullen ASC

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Posted 15 August 2010 - 08:31 PM

Thank so much. I'm sorry but I'm still a bit confused about going from say 16:9 to 2.39:1. In what way is the image changing?

I'm also still confused as to whether the image gets wider or taller or both when we use bigger sensors? :(


I'm not sure you understand what a ratio is... 16:9 just means that it's a rectangle that is 16 units wide by 9 units tall. It's just a shape. 2.39 : 1 means a rectangle that is 2.39 units wide by 1 unit tall. It's a wider (horizontally longer) rectangle than 16:9, which mathematically can also be described as 1.7777.... : 1.

Whether you want to describe a wider rectangle as being horizontally wider or vertically shorter than a less-wide / more-square rectangle is up to you. Depends on how you draw them, do you pick a constant height or a constant width, or split the difference?

None of this has anything to do with resolution or sensor size. It's merely a SHAPE, the shape of the rectangle.

Sensors comes in different shapes and different resolutions. "Bigger" in this case usually means physically bigger, but whether it is mostly bigger vertically or horizontally than a smaller sensor just depends. The Full-Frame 35mm sensor as in the Canon 5D is 36mm x 24mm, which describes a 3:2 or 1.50 : 1 rectangle, depending on how you want to do the math, it's the same shape. An APS-C sensor as in the Canon 7D is 22.3mm x 14.9mm, which is also about a 3:2 or 1.50 : 1 rectangle. But it is overall physically smaller than the FF35 sensor, just equally smaller in both directions.

Here are some old charts I drew about camera and projector apertures:

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#7 Jim Nelson

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Posted 16 August 2010 - 09:28 PM

Thank you so much for your help. Things are getting a lot more clear now :)

One thing that still troubles me is that, for example, if we have a 16mm film and a super 16mm film. I know we get more image from the super 16mm because it uses more of the film. But what I don't understand is: is the image that we get wider or taller (or both) than the image of a 16mm film. (width and height).

Because I know the bigger the sensor, the bigger the field of view. So is this field of view bigger in terms of the height or in terms of the width?


Also, in the diagram it show that 1.85 widescreen is shorter than 1.33. Does this mean that we lose some of the top and some of the bottom of the image when we use widescreen?


I'm so sorry if I'm being a pain. It's just this small part that's still bothering me. Apart from that I understand :)

Edited by Jim Nelson, 16 August 2010 - 09:32 PM.

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#8 David Mullen ASC

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Posted 16 August 2010 - 10:02 PM

One thing that still troubles me is that, for example, if we have a 16mm film and a super 16mm film. I know we get more image from the super 16mm because it uses more of the film. But what I don't understand is: is the image that we get wider or taller (or both) than the image of a 16mm film. (width and height).

Because I know the bigger the sensor, the bigger the field of view. So is this field of view bigger in terms of the height or in terms of the width?


Also, in the diagram it show that 1.85 widescreen is shorter than 1.33. Does this mean that we lose some of the top and some of the bottom of the image when we use widescreen?


I'm so sorry if I'm being a pain. It's just this small part that's still bothering me. Apart from that I understand :)


Super-16 film uses 16mm stock with sprocket holes running down one side only, so it can expose a wider area almost out to the edge of the stock, the edge opposite the perf row. So it is the same height as a regular 16mm frame but a little bit wider horizontally. 16mm prints also only have sprocket holes on one side but the opposite edge is used up by the optical soundtrack stripe. So Super-16 exposes picture information in that soundtrack area, so you can't make a sound 16mm print from a Super-16 negative unless you want to chop off the edge of the picture because of the soundtrack, or reduce the image to fit within the width of the regular 16mm projected area. That's why Super-16 is really meant for blow-up to 35mm, or for transfer to 16x9 video.

A bigger sensor sees more of the lens' projected image so the field of view is larger, unless the image starts to vignette on the wider sensor (because the lens was only designed to cover a smaller sensor area.) Whether the field of view is bigger vertically, horizonally, or both just depends on if the bigger sensor is bigger vertically, horizontally, or both.

If you shoot with a square negative, then a widescreen shape involves not using the whole height of the negative (unless you use an anamorphic lens to squeeze a widescreen image onto a squarer negative.)

So yes, the 1.85 format wastes some of the 4-perf 35mm negative and print area since Full Aperture is 1.33 : 1 (4x3). The 2.39 anamorphic lens ("CinemaScope") process doesn't because it squeezes the image horizontally by 2X to fit onto a squarer shaped negative. But the 2.39 Super-35 spherical lens process wastes a lot of the 4-perf 35mm negative.
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#9 Jim Nelson

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Posted 16 August 2010 - 10:18 PM

Thank you soooooo much. It's finally cleared. You're very helpful :)

Just one more thing if you don't mind concerning the image wasted because we go from 1.33 to 1.85 widescreen. Is the top and bottom of the image also lost when we go from, for example, 4:3 to 16:9 or 16:9 to 1.85:1?
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#10 Adrian Sierkowski

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Posted 16 August 2010 - 10:50 PM

4:3 and 16:9 are just other ways of expressing film aspect ratios. 4X3 is about 1.33:1 and 16:9 is 1.78:1, which is, in reality extremly close to 1.85:1 (as in I don't notice the slight extra black bar on my 16x9 TV ;) )

So on 1.78:1 (16x9) to 1.85:1 you will "waste" a bit of the display (normally) but not by much. Now, if you go 1.33:1 to 1.78:1 you'd loose approximately the same as going 1.33:1 to 1.85:1.

So essentially, same rules as film apply, we're just expressing the aspect ratios in differing ways.
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