14th January 2006
I am no expert on miniatures so need a little help. Compositing etc are no problem done that countless times. I am shooting a miniature of a large building coming out of the desert floor. The model will also telescope out - in other words sections grow out from themselves.
We are shooting the model first then the desert backgrounds. The model is 15ft high - the scale is 50:1. Speed should be around 160 frames. I am assuming lenses should be the same but we should be 50 times further away from the desert as we are the building - is that log or a straight multiplication. The height should also be altered - what formula??
I am thinking of lighting the building with a 100kw soft sun through a little diffusion. There will be some sand etc in the air.
Any other suggestions or anticipated problems.
Yes, distance scales - if your miniature is 1/50th scale and your background plate is full size, than that part of your background which is supposed to be where your building is should be fifty times further away from the lens than the miniature is when you shoot it... all other things being equal etc
that also means that if your camera is looking at your miniature from six inches off the ground and pointed up let's say twenty degrees, then the same lens on the plate camera should be pointed up twenty degrees and twenty five feet off the ground...again...all other things being equal.
Bear in mind that perspective is a function of camera position, not camera focal length. We often shoot elements with a tighter lens than would be a strict match in order to have it bigger on the neg for better resolution and matte extraction, but we will endeavour to put it at the correct distance so the perspective is correct. This gets cheated too, sometimes but it is good to know the rules before breaking them.
The other thing to pay attention to is depth of field - that scales too.
You need to hold focus on your miniature the same scaled distance as you would if you were shooting this as a full size building, and your background plate depth of field and focus set should match the miniature.
Remember that your frame rate issues are with regard to making physical stuff look like it is acting the way it is supposed to... but ultimately, it is a matter of having the right number of frames for the final shot - I can't comment on frame rate without knowing more of what is happening on the miniature
You might consider shooting your "sand and dust in the air" as a separate pass for a sep. element to comp in - this might be a bad idea or a good one depending on lots of other elements that can't be gleaned from your initial question, so I am not suggesting that you do this but merely bringing it up as something to think about – depending on lots of stuff....clouds of dust in front of blue or green screen are really hard to key and can totally screw up the matte extraction of the rest of the scene