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Nyx2095
03-20-2006, 04:55 PM
So I'm making my own renderers, and I typically always use the same FOV angles... But my images look a bit different from the typical GI scenes. I believe the problem is that my FOV angles are simply too large.

I typically use a horizontal FOV (all the way left to all the way right) of 90 degrees and a vertical FOV of 73.74 degrees (4:3 aspect ratio).

I'm wondering what are the typical horizontal and vertical FOV angles artists use? I'm also wondering what would be the FOV angles of a 35mm camera, for example.

lehthanis
03-20-2006, 06:09 PM
Aspect ratio and FOV are only loosely related I think.

As far as 35mm camera is concerned...keep in mind that most 35mm camera's can handle multiple 'mm's' I believe 50mm is the typical artsy FOV. 50mm:39.598deg and 35mm:54.432deg

I use max so I dont' know how to tell what the individual FOV of up/down versus left/right is, but the aspect ratio is easy to find.

My FOV for the Elder Brain current render in my sig is 45 degrees...with an aspect ratio of 1.333~ (800x600). Thats 43.456mm.

I'm not a photographer, but I THINK 50mm is the FOV where there is no fisheye effect, but I may be wrong.

Nyx2095
03-20-2006, 06:20 PM
Aspect ratio and FOV are only loosely related I think.

Well usually people give the horizontal FOV, and the aspect ratio tells you what the vertical FOV has to be. You can set the horizontal fov, vertical fov and aspect ratio independently, but it may look a bit strange if it's not coherent.

I'm not a photographer, but I THINK 50mm is the FOV where there is no fisheye effect, but I may be wrong.

Well I would like to see what other people have to say about this. I would definitely like a FOV that feels more natural and "photo-like", with no fisheye effect.

Saturn
03-21-2006, 09:08 AM
well 50 mm alone like this with no support info mean just nothing.
You have to know if you are in 35mm, super 35, 16 mm, etc... because the same focal length on different support give you an another angle.

About the 50 mm is usally refered to 24x36 support and it the angle that is closer to human vision.

To get something more "photo-like" isn t a matter of angle but more on Lens phenomen such as vignetting, lens distortion, DOF, grain, etc...

I think the best is to buy a SLR digital camera and to pratice photography, that will help you a lot. Have also a look to www.dpreview.com (http://www.dpreview.com)

scrimski
03-21-2006, 09:52 AM
Actually it is hard to say which focal length and what the human eye has, because it's changing all the time caused by the way the human eye works: based on a (very high)multiple change of view, focus and point of interest per second the human brain kind of calculates a picture what we assume as what we see. That's why almost everything you look at is sharp and never out of focus and that's why we have a field of view which is around 180.

A focal length around 50 mm is assumed to match the perception of the human eye, but it depends on the person, higher focal lengts don't create an artificial impression that much like smaller focal lengths do due the lack on distortion.

Nyx2095
03-21-2006, 04:38 PM
Well I changed my renderer code so that I only specify the horizontal camera FOV and not the vertical FOV... That way I can, to some extent, vary the image resolution in any way I like without running into vertical compression issues. So the rendered image size is independent of my scene description (which specifies camera parameters such as the position, orientation and horizontal FOV).

For now I think I will try to make renders with a 45 degree FOV and a 1:1 aspect ratio (instead of 90 degrees and 4:3)... I will see what that gives. I may adjust the canvas size depending on the scene. I'm thinking of modelling one that will be rather vertical right now... And by modelling I mean hand-plotting the coordinates in a text editor, as I don't have model support yet ;)

Saturn
03-21-2006, 05:52 PM
By the way :

w = film width in mm (e.g., 36) (= h * aspect ratio)

d = lens focal distance in mm (e.g., 50)

Horizontal FOV = 2 * atan( ( 0.5 * w ) / d )

pgraham
03-21-2006, 06:43 PM
my first cgtalk post was on this topic: http://forums.cgsociety.org/showthread.php?t=312450

There's a similar, more basic answer here from Jeremy Birn: http://forums.cgsociety.org/showthread.php?t=287977
(don't read the post, just the answer :) )

For the record, changing the FOV doesn't create the "fisheye" effect, just perspective distortion. Fisheye is when straight lines appear curved in the image. Renderers usually will not render fisheye.

Nyx2095
03-21-2006, 06:51 PM
my first cgtalk post was on this topic: http://forums.cgsociety.org/showthread.php?t=312450

There's a similar, more basic answer here from Jeremy Birn: http://forums.cgsociety.org/showthread.php?t=287977
(don't read the post, just the answer :) )

For the record, changing the FOV doesn't create the "fisheye" effect, just perspective distortion. Fisheye is when straight lines appear curved in the image. Renderers usually will not render fisheye.

My first raytracer did (by mistake). I was actually rotating the rays instead of sampling from an image plane... Effectively sampling from a portion of a sphere... It looked rather strange.

But yes, I always felt the need to use a wider FOV when programming my 3D engine, because with a narrow FOV, it felt like you weren't seeing anything (not enough information on your surroundings). But it was strange, because although games like Quake 2 and Half-Life used a FOV of "90", or so it seemed (that is what the console variable was set to by default), mine actually looked quite different, perspective-wise, as if objects were always too small.

As far as "considering how people will be viewing the image", I've heard that many times before, but never found it to be particularly useful. I want to make renders that feel similar to good photographies. Now I know not all photographs use the same lenses and film, I know that photographs like to experiment (at least some do), but there is such a thing as a "typical configuration". I'm curious as to what is *most widely used* by photographs in terms of film and lens, and what the resulting FOV would be. Certainly some photographic equipment has to be more *common* than others for taking pictures of rooms and medium-sized subjects (1 to 1.8 meters) within a medium distance (3 to 7 meters).

jeremybirn
03-22-2006, 12:08 PM
I'm curious as to what is *most widely used* by photographs in terms of film and lens, and what the resulting FOV would be. Certainly some photographic equipment has to be more *common* than others for taking pictures of rooms and medium-sized subjects (1 to 1.8 meters) within a medium distance (3 to 7 meters).

Common for architectural photography of a room would be a typical wide-angle lens of about 18mm to 28mm (or a 90 degree to 65 degree FOV.)

Common for pictures of medium-sized subjects, for a catalog or something, would be about a 50mm lens (or 40 degree FOV.)

Common for a portrait of a person would be about an 80mm lens (or 25 degree FOV.)

These are for stills on 35mm film.

Another way to look at what's common is to look at compact cameras sold to consumers that don't have interchangeable lenses. A typical point-and-shoot camera with a 3x zoom lens built in will have a FOV ranging from about 50 degrees to about 16 degrees. Users often zoom out to 50 degrees when they are taking pictures inside, and zoom in to 16 degrees when outside. Cameras with bigger zoom lenses, like a 12x lens you could use for sports or photographing wide animals, go down to 4 or 5 degrees.

-jeremy

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