matching maya camera to sdx 900

#1

hi,

i need to match a maya camera with an sdx 900 camera, with a 8.7 - 165 mm fujinon aspheric zoom lens. Apparently its got 2/3" 3CCD chip inside the camera. I will be shooting 4/3 and i hope to also want to find determine how much lens distortion is present when shooting. Does anyone know how to figure out these details in maya from this information:

angle of view (of course i will note down what the focal length is for each shot):

camera aperture:

lens squeeze ratio (i dont know what this does):

and any other neccessary details.

oh also, does the scale of the camera in maya have to be the same as the real sdx 900, i would have thought it does as a bigger ccd chip and lens could capture a larger view…

thanks,

sam

#2

you would probably get answers in the maya forum:D

#3

Okay here goes…

Regarding FoV, sensor size and focal length. I’m unable to find any information regarding the lens of the camera - specifically what it’s FoV range or it’s equivalent 35mm focal length range are, both of which would have been useful to know and I reckon I could have given you a fairly accurate sensor size for Maya which would have allowed you to enter the same focal length on Maya as what’s marked on the lens.

As a starting point you can try what Panavision.co.nz list as the size of a 2/3" sensor. (Note I’m using 4*3 measurements here, that’s why the width below is different from their site. And also Maya uses inches for it’s sensor size (known in Maya as aperture width and height)).

7.18989mm * 5.39242mm (4:3)

Best way to test this is to shoot an object (a box is good) of known dimensions at various focal lengths (use the markings on the lens), import the footage into Maya and line it up to a 3D model with the same dimensions as the real object you filmed. If the sensor size is correct then setting the focal length in Maya to the same focal length used should make it fairly easy to line up (except at wide angles where lens distortion is introduced - I’ll get to that soon).

If that fails then your going to need to measure the FoV of the lens at various focal lengths.

For lens distortion, print out a grid (here’s one I found) and film it. When your shooting the grid the camera should be perpendicular to it. Also for each focal length the grid should fill the frame, so you’ll have to move the camera or grid (whichever is easier to do so).

Import a still of each filmed focal length into photoshop, after effects, shake, nuke, etc (there are a bunch of programs which allow you to do this). Use a lens distort filter/node to remove any distortion from the image - so the lines in the grid are all straight. Record the amount used to undistort the image, the inverse of this will be used to distort the CG to match the footage you shot.

Regarding the lens squeeze ratio (pixel aspect ratio), Maya has a default resolution setting for PAL/NTSC 4:3 in the render globals for both square and non-square pixels.

Hope that helps in some way, I’ve left a bunch of stuff out, hopefully someone else can fill in the gaps.

Reading recommendation… The Invisible Art of Matchmoving

#4

thanks alot, that was really helpful,

i was just wondering what the value 2/3 inches actually refers to, is it the area of the ccd chip?. and if it is, i heard in a tutorial that only 0.666666 of that value is actually used to record on, do you know anything abuot this.

Sorry to be a nusance, but i have to be sure on the width and height of the aperture so the angle of view is accurate for my block tests in maya, i want to get all the shots planned with the closest equivalent setup in cg so when i do the real shoot i have all the compositions planned. I dont have access to the sdx 900 for a month.

how did you figure out those values by the way from the 2/3 inch info you got from the panavision site??

OH sorry one more thing, when i scale the camera in maya i guess it has to have the same relative dimensions as the sdx 900, how can i find out how far away the ccd chip is from the lens on the real camera to figure out how best to scale it in maya, and also where to put the pivot for the supposed tripod.

thanks, sam

#5

This might help explain some things… http://www.dpreview.com/news/0210/02100402sensorsizes.asp

I can’t seem to get to the Panavisions NZ site at the moment, but they have a knowledge base section which lists common film/video formats. Because their listing for a 2/3" sensor is based on a 16x9 sensor I cropped the dimensions I gave you to 4x3. I have no idea how they came up with their measurements for the video formats.

It is possible to figure out the size of the imaging area (the exposed part of the sensor) to a reasonably accurate degree by figuring out the FOV of the lens. Some manufacturers list this information in the specs of the camera or lens - in the case of the SDX-900 being just a body it doesn’t list lens specs. The other way is to measure this yourself, but you’ll need the camera. Stu’s DV Rebel Guide outlines how to do this - I can explain it, but it’d take some time and I wouldn’t be able to do it as good as Stu.

If your prevising shots before the shoot, then your going to have to do with near enough at the moment. Best to create a piece of proxy geo to represent the camera’s physical dimensions in Maya and leave the camera scale at 1. If you creating a non-nodal camera rig inside Maya to better match the real camera then without actually figuring out where the nodal point is on the lens or how the camera is balanced on the tripod then your going to have to put up with approxiamations of those variables.

#6

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