Aperture height

[marc]

Hello, everyone,

I want to start compositing CGI with realworld images. When I wanted to match LWs camera settings to the one of my DV camera I realized that I don't know how to do this.

How do I calculate the aperture height from the CCD size information? I have a 1/3.6 inch CCD.

Cheers,
Marc

[richpr]

Some cameras, like my Nikon Coolpix, store lots of info in the image...

You would know the resolutions of the image, the f-stop of the lens as you were shooting and maybe other things like shutter speed, etc.

[pblacklock]

look into the camera items properties then click on the down arrow of the aperture height button and choose your 1/3 ccd.

Paul

[marc]

richpr,
I even have a Nikon Coolpix. But in this case, I meant a digital video camera (Sony TRV60/70).

Paul,
I had found the presets even before I wrote my initial post. But I wasn't content for two reasons: First, my CCD is 1/3.6, not 1/3 (yeah, I am extremely picky).

Secondly, I would really like to know, how to calculate this value. For example: When I record in progressive mode, the complete CCD is being used. Does the aperture value of the preset take this into account?

Marc

[pblacklock]

Marc,

no idea about the progressive scan mode and the aperture setting, hopefully more knowledgeable people will provide an answer to your question.


later,
Paul

[richpr]

From here (http://www.newtek.com/freestuff/lwhelp/content/013_Camera/006_camera_lens.htm)

Aperture Height

In LightWave, you can change the size of the virtual film that the camera uses by selecting the Aperture Height button. Changing this setting affects only the strength of the Depth of Field effect (see below) and the Lens Focal Length. When you generate LightWave imagery for film photography, use the same film size used for the project’s real world camera, so you match the optical characteristics of that camera.

NOTE
Aperture Height is always listed in inches, even if you are using a metric unit system.

[stib]

When you say that When I record in progressive mode, the complete CCD is being used.
Marc I'm guessing that this means that both fields are being captured in each frame, thus using the complete CCD, rather than normal interlaced mode which only uses half the lines for each field. This won't affect the aperture height.

Also you can set the aperture height to whatever you want it to be, you don't need to use the presets. Just type in 1/3.6" in the field, and LW will even do the maths for you.

[Hervé]

Can I jump in...?
well it is going to be hard to calculate the exact aperture... I am using a prog from realviz that exports my camera settings in LW ... and then it is very accurate.... I am using a still camera sony 707... zoom max wide... so in case someone interested....

Cheers... Hervé

[Hervé]

I forgot to say... you can see an enveloppe also... why.? you asked (yes why , coz I shoot all the photos using exactly the same settings for my cam....) I guess just because the focus change a bit at each photos ( with autofocus at least....

But I realize you talking about a video cam... well any 3D tracker will output that info for you....

NT , I guess will be well inspired to add a 3D tracking in LW (even as an option)... it would be a good complement for people that want to integrate their anims in live footage...

Cheers, later, Hervé

[stib]

Oh yeah I forgot to mention. I thiiiink CCD measurements are taken diagonally, like the measurements of tv screens. So it wouldn't be 1/3.6 it would be erm lets see [digs out pencil and paper, remembers pythogoras's theorem]
mebbe..
height = 3x
and because we're dealing with a 4:3 aspect ratio
(at least as far as the CCD goes,
I know you can do widescreen on that camera,
but it's just stretching the pixels):
width = 4x
now
diag^2=width^2+height^2 (pythagoras)
NB ^2 means squared, sqrt(n) means square root of n
diag = sqrt(width^2+height^2)
so
diag = sqrt ((3x)^2+(4x)^2)
= sqrt(9x^2+16x^2)
=sqrt(25x^2)
=5x
so
x = diag/5
= (1/3.6)/5
x = 0.05555555555555556
height = 3x
so aperture = 0.1666666666666667"


maybe you should check that though

[Red_Oddity]

:eek: :confused:

[stib]

whew what was I on? Late.. night.. too.. much.. caffeine. must.. do.. trigonometry..

[marc]

Thanks, Stib,
I tried to do the same calculation in my head before - too lazy to write it down - and, of course, came up with strange results. I'll better try your value.

Herve, a 3D-Tracker integrated in LW would be extremely nice. But, considering that professional Trackers (like Boujou) cost more than LW, I doubt it.

Marc

[Hervé]

I know Boujou costs an eye and a leg... did you checked realviz MatschMover... a little less expensive...

[txbob]

A quick and dirty answer can be figured out easily. Take a image image with the camera, and measure the distance to various items in the shot. Get basic measurements of the items. Make a dummy scene in lw and place the camera, and dummy items in the the same relative positions. Load the image into the background. Adjust the lw camrea until the lense paralax causes everything to fit correctly. Viola!

When doing composite shots I always try to be on-set when the plates are shot to get just such measurements. I also like to videotape a bit with a small camcorder to get lighting references.

[stib]

that would work, but only if you knew the lens focal length. Because the camera's field of view is determined by lens length AND aperture height, you would have to know one to work out the other. So if you shot on 35mm film on a 50mm lens you'd get the same FOV as you would on a super -8 camera with a ..erm 12mm lens (or thereabouts). But your depth of field would be way different.

BTW Marc, from http://www.isorainbow.com/tech/lensterm.html

"IMAGE SIZE Reference to the size of an image formed by the lens onto the camera pick-up device. The current standards are 1", 2/3", 1/2", 1/3", and 1/4" measured diagonally."
my emphasis added.
Amazing what bits of trivia I can dredge up from film school..