Focal Length?

[stunndman]

yes -> http://www.google.at/search?q=what+is+the+focal+length&ie=UTF-8&oe=UTF-8&hl=de&meta=

[mark_wilkins]

yeah, although you need to remember that the field of view of a lens is different depending on the size of the film format. Soooo the FOV of a 24mm Canon lens used to make a 35mm still will be more like a 40 (or so) used with an Academy-aperture motion picture frame.

[danylyon]

thanks so far..

Well.. the 35mm Canon lens turned out to have a an Angel Of View of about 36.64 and a Focal Length of 30.38 (that's what a 3D tracker said).

Now.. how do I come up with those numbers?

I need to know the same thing from a 24mm / 50mm / 55mm / 85mm lens too.

It's shoot on 35mm.. Full Aperture I would assume (there was no recording of sound). It has been Telecined to PAL resolution.

Why does everything turn out more difficult in the end.. why oh why..

[danylyon]

I think I'll just change the other Lenses respectively.
It might be due to scaling in telecine (I told them about 5 times not too..*grr*)

I don't have the time to sort things perfectly out.. I'll creatively fix everything up.. *hurray*

Motion Control is a nightmare.

[mark_wilkins]

Scaling in telecine will never make a lens appear *wider*, as that would imply increasing the field of view, which is already defined as the angle across which the camera captures all of its image information. In other words, if it looks like a 30mm lens after telecine (and you don't have black around the edges) then you had extra image information at the edges to start with.

HOWEVER, you need to keep a few things in mind:

* If you were shooting, say, Super 35 and your 3D tracking software were told it were looking at an Academy plate, you could well be told that your lens was 30mm when it was actually 35. The reason is that the software would be assuming that the picture came from a smaller part of the film, and thus required a wider lens to capture it.

* If you were assuming that your image were cropped in a certain way, and plugged those assumptions into your 3D tracker, while the telecine operator dutifully set up to capture all the image information on the film, edge to edge, you'd have the same problem.

* Commercial 35mm still lenses are somewhat variable in focal length. Some 35mm lenses will be closer to 30mm and some may be a little longer. Angle of view can be affected by mounting adapters and so on, although usually that will make a lens seem longer rather than wider. Usually this variability doesn't matter because people aren't relying on the focal length to be strictly accurate, although the difference between 30 and 35 is more than I'd normally expect.

-- Mark

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