I have created a virtual scene of my door frame, molding and foam core polygons in cd4 and want to render it out so that my projector projects the render back onto it's self. I have been trying this for some time and have been failing constantly. Lens distortion, wrong size etc etc.. Does anyone have any experience doing this? My goal to to project accurately back onto geometric objects for an art piece. BTW I'm using an Optoma EzPro 739 Multimeida Projector. When I plug in the specific focal length: 28.04 mm and Aparture width of 2.5, the camera image appears too close up.
Re: camera settings for projector by Lennart Wåhlin on Mar 12, 2009 at 11:25:20 pm
Looking at the specs of the projector we have:
DLT width 18mm, height should be 13.5 (4:3 ratio).
That gives an aperture of 22.5. (Your 2.5 might be a typo?).
(Aperture and focal length is always in mm.)
The "digital" equivalent of the focal length 28.4 (35mm camera) is 14.75.
You can use a dof calculator to check this, and I even made
a free one for Cinema that you'll find at:
www.tcastudios.com -> xfiles -> SteadyTOOLS.
Hope this can help a bit and I'm not missing you intention.
Re: camera settings for projector by Nathan Byrne on Mar 17, 2009 at 8:00:48 pm
Thanks so much for that. I did manage to install the Object user preset Steady_DOF_R10, and there are a great amount of controls that this allows. Did you design this (if so, I'm in awe).
However, I'm officially overwhelmed.
My intention is to create a scene in C4D (wall's and geometric shapes), create a camera, place it in the scene and render it out at 1024x768. Play it back through a projector and have it line up with the real world wall and geometric shapes.
Here is a link to a very simple project and the specifications for the Optima 738 projector. If there is any chance anyone might be interested in telling me how this can be accomplished, I would be SO greatful.
Re: camera settings for projector by Lennart Wåhlin on Mar 17, 2009 at 10:33:39 pm
I can't say I see much of a problem here
Model your stuff at scale, place the camera in the scene
corresponding to where you will put your projector in real life.
(Thou try to have it placed horizontally)
In SteadyDOF type in the values from earlier post of mine
(I used the same tech info as you provided in the dload.)
Have your render output set to 1024x576.
The result is as good as it could get.
You will still have to fine adjust the projectors zoom
and keystone in the end.
Have in mind that the Cinema camera is a "pinhole" camera,
it has no physical lens artifacts.
Re: camera settings for projector by Douglas Kerr on Mar 18, 2009 at 8:08:45 pm
Very interested in this technique I've seen a few places.
I didn't think of using C4D to emulate before hand, why have you gone that route out of interest? Would have thought it's quicker to place the objects and mark where they are positioned and then use visuals software like Modul8 or VDMX to map screens for each surface you want to project onto.
Re: camera settings for projector by Nathan Byrne on Mar 18, 2009 at 8:26:34 pm
My goal is to give the illusion of parts of a stationary object are moving (i.e. a building facade). This would require creating 3D elements and shadows.
BTW ... I working on tests as we speak and I'm still pulling my hair out.
If I put in the exact camera (projector) specs, in this case, as Lennart says a focal length of 14.75 and a aperture of 22.5,I'm still too far away from the object. Even disregarding the correct focal length and putting in a number that works 2 dimensionally (i.e. a focal length of 70mm), the three triangles don't join correctly in the middle. When the projector (camera) is 68 inches away from the wall, the real life tetra pretty much takes up the whole screen. I'm currently considering my projector zoom maybe interfering, so I'm checking that now.
I keep reading of people using Cinema 4D to map out big theater productions, I wonder what there workflow is?
Re: camera settings for projector by Nathan Byrne on Mar 18, 2009 at 9:30:17 pm
Just as an update. I've been trying the fix the perspective problem, by getting the three sides of the pyramid to join up. I went back to Lennart's DOF calculations and used modul8 to to resize, reposition etc. The result was a bust, it's perspective is still not correct.
My theory is that the the C4D camera projects symmetrically (i.e. the same height, north and south of the camera's center), while the real projector only projects north. The projector is designed to sit on a desk and project so the bottom of the projected image is a couple of inches above the height of the desk.
This difference in lens throw rotation would certainly alter the prospective of the objects in the scene. Is there a way to adjust the throw rotation and dimensions of a camera?
Re: camera settings for projector by Lennart Wåhlin on Mar 18, 2009 at 11:26:03 pm
No pun, just an observation, there must be something fundamental wrong
in your settings, like scale or projector settings.
Leaving all mathematics aside, if you have modeled your subjects
to scale and placed your camera in the scene where it should be in
real life, setting it to approx values, looking thru it and render, it should
maybe not match perfectly, but be in the area of close enough.
There should be no reason why the subjects should be way to big or small.
So, two things.
Check out how the zoom really works in the projector.
Then, the offset you are talking about (projector projects asymetrically
up, (north I suppose)) is the "FilmOffset" parameters in the Cinema Camera
Object.
The tech info for the projector, if I recall, states a +-16 degrees range for this.
Still, as mentioned before, as the Cinema camera is a pinhole camera,
no lens distortion is "made". That sort of keystoneing has to be done
in the playback program. Or be made via a post app.
Most of my work is projection and LED content, but I must confess in a
much larger scale, so the projector side is handles by the projector/LED
contractors.
Still, no matter how much preparation , things are tweaked on site, both
contentwise and hardware.
Re: camera settings for projector by Nathan Byrne on Mar 19, 2009 at 1:46:02 pm
Lennart,
Thanks so much for helping me through this. I agree that I'm missing something fundamental here.
My thought is that scale problem must have something to do with the throw ratio of the lens. I tried a similar experiment with another projector and had a wildly different result.
My projector has a Throw Ratio of 2.00-2.40 and a Zoom Ratio of 1.2. I looked into the zoom, however the projected image was still much smaller than the real life object. Do you have any idea how the Throw Ration is related to the C4D camera? Is it already accounted for by the focal depth and the aperture?
I found a great projection calculator at projectioncentral.com I copied the specs:
Re: camera settings for projector by Lennart Wåhlin on Mar 19, 2009 at 7:44:26 pm
I frankly can't tell how much help I can provide until
you have figured out the projector(s).
Try make a 1x1 meter square with a cross in it from corner to
corner and a circle in it.
Make it in Cinema and tape it on the (real) wall.
Test and check until you find out the proportions of your setup.
This is the prime way we do it. The designer and contractors provide
us with messurements, we then do "Default Nulls" and they confirm it.
Once the Nulls are perfect/confirmed we can start producing the content
having the nulls as our reference.
Re: camera settings for projector by Nathan Byrne on Mar 23, 2009 at 9:43:41 pm
Okay,
I've managed to get everything nicely aligned with a two dimentional chart. A couple of circles with an x through it. I also played around and made some nice 3D shapes play with the chart.
Yay. BTW to make this work, I set the correct information in SteadyDOF and then altered the Aperture Width to 18.3 in the object properties section.
Next step, make it work with a real world 3D shape where correct lens distortion fits correctly.
Re: camera settings for projector by Alex San Agustin on Oct 28, 2009 at 4:58:57 pm
Hi everyone,
I´ve been carefully reading your discussion which is really interesting for me.
I have an important question related to projecting on 3d geometry and i suppose that will be interesting for someone else.
In most cases (like Nathan´s example), projector perspective and spectator´s viewpoint are the same, or are supposed to be equal. Then workflow is conceptually easy:
1. map reality
2. apply lens correction
3. make a 3d model
4. process it
5. render it (projector position) with lens correction
6. project it
Ok, but what happens when projector´s position and spectator´s viewpoint are not the same?
For example sometimes you have to work with several projectors that project on the same object. This problem can be solved by placing the projectors close together, then each perspective will be nearly the same.
Ok, but if projectors are placed in order to cover for example an sphere we are going to have 3 different perspectives: each projector perspective (that will be completely different) and spectator´s viewpoint...
