Lens Focal Length, Imager Size. and Aspect Ratio
galaxiefilm_9f95c8c177
Posts: 4
Has Carrara 8.5 addressed the issues of the relationships between Lens Focal Length, Imager (or Film) Size, and Aspect Ratio like Lightwave does? I'm still using Carrara v:8.
Many of us want to use Carrara to create character animations for compositing into live backgrounds that were shot with a digital cinema camera. But to be able to match the correct perspectives, we need to be able to set our virtual cameras to match the actual camera used to shoot the live BG with--i.e., matching it in terms of the image or film size, the aspect ratio, and the focal length used on the BG plate camera.
Originally, Carrara was designed to simulate a 35mm still camera with appropriate focal lengths. I can convert that to what I need mathematically . But while it's fine that I can create an aspect ratio in the Render Room for my camera, by allowing us to resize the production frame in the Assemble room, you destroy the accuracy of all these relationships. Not good.
So, has this problem been addressed now? If not, how do I resolve the issue?
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Comments
What "problem" are you talking about specifically? Yeah, you can set focal length of course, and also aspect ratio/image size, and you can lock the production frame so that doesn't change. But I think it has always been that way, hasn't it?
Usually the biggest problem is getting the corresponding settings from the real world camera, not the CG camera. You can always tweak the CG camera to match. Unless you really need an absolutely exact match ?
I need as exact a match as I can get. I'm executing left-eye & right-eye Stereoscopic views.
Is there a way to lock the production frame so that I cannot resize it by grabbing it's corner in the Assemble Room so that it absolutely will match a 35mm 8-perf still camera?
Yeah, in the View dropdown menu...Lock Production Frame
EDIT:
(Cross-post)
Yeah, like Joe said:
View > "Lock Production Frame"
But if you also go into Render Room settings, output tab, place a check mark into "Keep Aspect Ratio", will lock the ratio from changing.
And BTW, as far as an "absolute match", I wish you luck. Yeah, Carrara's camera is supposed to be based on a 35mm. However, I don't recall hearing anyone here ever discuss matching cameras and doing tests on stuff like that, because I doubt many here really care about stuff like that. So you may be treading on new ground.
...and like I've said in another thread today, it can be very helpful to deselect "Show in 3D View" on the actual camera, so that you cannot actually see the camera's avatar, after you have it in the correct position.
Make your stereoscopic duplicate and parent them to a Target helper, or just group them and select the group to move them around... any similar method of keeping the two eyes in their correct position.
...and then don't look through those actual cameras while working in the scene. Instead, use the Director's Camera. To use the Director's camera to then look through the eyes of the other, just use "Set position to:" from the same upper left menu where you chose which camera you're looking through.
Dartanbeck, do you know if anyone has done any tests to match the Carrara camera to a real world camera, and seeing if it really does match a camera with 35mm EFL?
I remember someone doing some posts on match-moving (am I getting the term right) which seemed to involve a real world camera with a 3d object. I remember it was some sort of Easter island statue that someone had put into a video clip he had shot of his backyard, moving around the object. It made it look like it was really there, and I would think to do that you'd have to have exact match of real world camera settings... but this is a little (lot) above my expertise so I may not know what I'm talking about... :)
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Fabulous input, guys.
Thanks so much!
Yes, I expect to do manual tweaking -- but getting me closer will help reduce that.
I sincerely appreciate your help.
-- Dave
I'm still not quite sure that I understand the issue though. Aren't these going to be images brought into the computer in some way? Just match the resolution... but I'm no photographer, so I am, therefore, clueless on the issue.
Paul Scammel used SynthEyes to match movement as seen here, in the Carrara 8 Promo Reel starting at 1:08 of the video, but that was a different topic too... but it may have been Paul....
Wow, can't believe you found that, and so quickly too! Yeah, that's exactly what I was referring to earlier. I don't recognize the name though, so I don't know what his profile name would be to do a search through the old forums, might be difficult to find the old thread where he was discussing it...
I use my Carrara Information Manual thread! :) I can dig pretty deep, pretty quickly! :ahhh: It's maddening!
Well it's quite a bit more than that...
I think the OP is going to take some video in the real world with a real camera and use that as a background, and composite some CG characters/animation, etc., on top of that.
To do that, it's very important that the renders out of Carrara look like they fit into the real life scene from the camera. Which means you have to match the following:
Camera focal length (zoom, wide angle, etc.), camera aspect ratio and image size, image resolution (you don't want your Carrara renders to be sharper than the background, for example), depth of field (so stuff is in matching focus in both layers), lens aperture, ambient light levels, ambient light colors, sun position, cloud cover (for shadows), light positions, types and characteristics, camera motion (called "camera tracking", making sure your Carrara camera has the identical motion as the real camera), auto zoom, auto focus, auto aperture, and so on.
Just one element of that is what the OP was describing, which is making sure the basic parameters of the lens and film/sensor in the real camera match your Carrara camera. So when you set, say, "50mm" focal length for your Carrara camera, it has to be the same as the equivalent focal length (EFL) for the real world camera. You don't want your Carrara image to look like it was taken with a zoom lens, but the background was taken with a wide angle lens. People will scratch their heads and notice something is wrong.
So what I was asking was, has anybody verified that the Carrara camera really does match up to a 35mm EFL on a real camera. Which means you take a real camera, set it up to take a foto of a simple object, and set up the same scene in Carrara, and compare the render with the foto. Or you can get fancier if you want.
In any case, if you're going to do any sort of real compositing using real world images and Carrara renders, you need to consider all of this stuff if you want it to look decent. Which is why I'm always encouraging people to use and compare reference fotos, and try to match your renders to reference fotos. It's an excellent way to get you familiar with the stuff you need to know if you ever do any serious compositing/VFX work.