Aerial Projection?

[Larry Rutledge]

I was reading articles/websites relating to mini35 type adapters, and the various necessary components. I came across a site talking about a homemade telecine device and in the text was a brief description of how a telecine machine works. Among the text was the following statement:

A telecine has internal optics and uses aerial projection of the image, where there is no actual screen in the optical chain, but the light is focused there anyway, so the video camera photographs it in mid-air.

Can anyone provide more information on how "aerial projection" works? I tried searching for more info, but so far only found links to companies selling devices that do it.

Thanks,
Larry

 

[rpster]

i just went thomson grass valley's website and looked up their telecine manual.
it doesn't seem like they use an "aerial projection" or any sort.
they just focus the image right onto the ccd device.

http://www.thomsongrassvalley.com/docs/Manuals/film/shadow/Shadow_Operating_Instructions_v247.pdf
page 327

 

[limehouse]

The Wikipedia entry also says they project onto a CCD.

http://en.wikipedia.org/wiki/Telecine#Basic_principle

 

[simonfilm]

Aerial projection

Aerial projection

I suppose that you are referring to a condenser lens system like this: http://www.moviestuff.tv/8mm_telecine.html

The cubic box on the right is basically a big convex or planoconvex lens and a mirror in order to flip the image. You can use a magnifying glass, but you would need a big one. Instead of projecting the image in a wall or a ground glass, the image is seen directly through the lens with no diffusion loss. The condenser lens transform the image from real to virtual, so you or a camcorder can see it directly without projection on a surface. (Of course, the projector lamp is not the lamp used for projecting on the wall, but a very low power one!).

A 35 mm camera lens acts like a small and low power projector, projecting the image on the film. I think that it is possible to focus a camcorder to a condenser lens that gets the image from the 35 mm lens, but:

1. With a ground glass you focus with the camcorder macro to a small area and it is easy, because the distance between camcorder and image (groundglass) is what is appears to be. But in the case of the condenser lens, you have to put the camera too much far away in order to see the virtual image (i.e. from 0,5 to 1 meter) and use the zoom (not the macro). So you need a big condenser lens, at least 4 or 5 inches.

2. I am not sure if this process ruins the shallow depth of field property of the 35mm lens, because it could be considered (or not!, I dont know) as a whole optic system with bigger depth of field.

Simon.