120 degree-wide lens equivalent?

[Webster Colcord]

Hey guys, this will apply to a CG render, but the lenses I'm using in Maya are equivalent to 35mm four-perf - hence, I'm posting it in this category. I'm going to put together a sequence for a 360-degree display and I would like to tile it in three 120 degree sections. The image is 10,053 X 720 pixels. I'm looking to find the lens that will give me a 120 degree wide view. Originally I thought I could do it using a 50mm lens in nine 40-degree sections, but I would rather do it with three sections to simplify the rendering.

 

Since all of the camera attributes are variable in CG, there may be some odd setting which would give me the equivalent, but I've got more experience with 35mm lenses than with CG lenses.

 

I know this has been done in 35mm before, but with more than three cameras shooting up into mirrors.

[Webster Colcord]

Just to follow up a little,

 

-each 1/3rd section comes out to 3351 X 720, that's 4.65:1 (and being CG, I can set the filmback to that) however I need to find the correct lens to not give any "repeating" movement at the point where the seam is (as would happen if I used a lens that was too wide). There's no overlapping between sections in this render.

[Chris Keth]

Just to follow up a little,

 

-each 1/3rd section comes out to 3351 X 720, that's 4.65:1 (and being CG, I can set the filmback to that) however I need to find the correct lens to not give any "repeating" movement at the point where the seam is (as would happen if I used a lens that was too wide).  There's no overlapping between sections in this render.

<{POST_SNAPBACK}>

 

 

If nobody else responds, I'll look it up tomorrow when I have my American Cinematography Manual with me.

[Bruce Douglas]

I'm looking to find the lens that will give me a 120 degree wide view.

 

If your program is based on 35mm Full frame (.945in or 24mm width), use 6.93mm.

If your program is based on Academy (.825in or 20.96mm width), use 6.05mm.

 

If you need more precision to avoid overlapping action use this formula:

 

(Format width / 2) / tan(Angle of view / 2)

 

I thought I would never have to use trig again if I went into film! :-)

 

Bruce Douglas, DP

Sao Paulo, Brazil

[David Mullen ASC]

Trouble is that the wider-angle lens you use, the more barrel distortion you get, making it harder to tile the images. You see this in Cinerama movies, which used three 27mm lenses in a row exposing onto three 6-perf 35mm frames to create a 146 degree field of view. Each panel has an obvious vanishing point and everytime to tilt the camera up or down, the horizon breaks off in different directions, etc.

[Chris Keth]

Trouble is that the wider-angle lens you use, the more barrel distortion you get, making it harder to tile the images.  You see this in Cinerama movies, which used three 27mm lenses in a row exposing onto three 6-perf 35mm frames to create a 146 degree field of view.  Each panel has an obvious vanishing point and everytime to tilt the camera up or down, the horizon breaks off in different directions, etc.

<{POST_SNAPBACK}>

 

 

Maybe using a lens a little longer and overlapping carefully might be a better solution?

 

 

In any case, it would be REALLY COOL to make an animation with the intent to project it in a very wide view like this but do it on a part-spherical screen like imax. That would be eyepopping.....or headache-inducing, as IMAX does to me.

[Webster Colcord]

Well, the folks putting the physical display together have informed me that there's actually a shader for Mental Ray that will render out a 360 view with the correct distortion for the curved screen.

 

You can download it from this guy's site:

 

http://www.sandstrom.on.to/

 

But for previs purposes, I need to come up with an approximation. I changed the "film back" in Maya to 3351 X 720, which is 1/3rd of the final image size. Thanks Bruce for the info but since I changed the format so drastically from 35mm, I actually need to compute for a longer lens. I've had a good result from a 75mm lens, but there's still a few issues at the seam.

 

It's for a gigantic display at E3.