Projector node

there a few things I d like to ask about the projector node.

1- why do we set the projector position then set the lens transposition relative to the projector instead of setting directly the lens position?

2- what is the lens diameter for?

3- what is the imagewidth on lens and what is it needed for?

4- are the shift x and y just for fine tuning?


hi Simone,

we thought it might be a good idea to have an icon, which just looks like your real projector to have a visual feedback, which allows you to compare real world with your virtual world. so the lens position is there to give you a nice representation of your real projector. on the other hand we thought it might be nice to be able to rotate your projector around its middle just like you would do it in the real world. therefore its origin was placed into its middle. (rather than at the tip of the projection cone, which is somewhere inside the projector)

lens diameter is really just to get a nice icon.

this parameter just reflects that the cone of the projector doesn’t start at the lens but behind the lens. with that info (together with the lens position) the module tries to calculate the tip of the projection cone (= the center of the perspective camera cone). this one is for fine tuning and not too important. it dollies your camera 1 or 2 cm back and forth.

shift x and shift y are for simulating the shift optics of your projector. it is very important to get them right.

hope that helps,

hi Sebastian and thanks for the detailed reply. I imagine that 1 has come to be by direct and long use of the node and common sense… the fact about rotating in its own axis (often a camera stand-like screw, dunno how you call it) makes it a really cool feature, I didn t think about it…
2 and 3 are self explaining
4 I still don t get it, I suppose they can be related to the fact that the cone broadcast by the optic is not a regular cone but it “tilts” on the y axis … if that s the case what is the x factor for? I suppose the cone to be symmetric on its vertical middle plane… oh maybe if I am projecting with a projector which tilts a bit on its z axis ? I mean tilting a bit on its side? Or am I just getting lost?

hi again
about 4 I got the link to this post

that seems to sort out my doubts, I ll need some time to dig into the info and make some tests, feel free to add any info you may think it can be of interest…

btw: haven t you started a sort of projector database with all the info for each model that has been tested ?

In my experience you need to measure the individul projector, since the projctors can vary a bit even though they are the same make and model. I have seen projectors with no X- lens shift actually having significant lens shift… but these projectors have all been really cheap.

So even though such a list would be nice, you would need to make measurements to get the parameters of your specific projector.


It seems like using the proper values doesn t work as well as tweaking th evalues here and there to make a simple box fit in proportion.
So my question at this point: how is your personal balance between the real world measurement you get and the fine tweaking you need to apply to make it fit with the reality?