Silent Running extras: Front projection - can someone point me to more info on this? (1 Viewer)

[Jeff Ulmer]

In the making of they show how they were using front projection for the SFX, however I am at a loss to understand how this would actually work. I understand they are combining live action with a still plate in camera, but what I don't get is how all the negative space that is to be replaced by the plate image does so without affecting the foreground image.

Today, they would use blue/green screen for these effects and do them in post production. They shoot the models, and anything blue is replaced by the new background. I could also see rear projection being used, since they are photographing a foreground object against a static background, so what you see would be what you'd get.

For Star Wars, they had an elaborate optical process for the space scenes, creating mattes for each ship and burning them into the underlying composite scenes. This is all done after the fact.

For front projection, how do they avoid getting the background image mixed in with the foreground? Does anyone have a pointer to a web site that explains this in detail? Curious minds want to know!

 

[Peter Apruzzese]

2001 A Space Odyssey also used this technique - mostly for the Dawn of Man sequence.

The way it works is that you put the background image in a projection unit of some kind (still or movie, depending on what you are doing). That is placed at a 90-degree angle to the camera lens. A beam splitter is then placed at a 45-degree angle in front of the camera lens. The beam splitter reflects the background image towards a special reflective screen that is placed behind your 'live' foreground objects. The camera shoots right through the beam splitter. If everything is aligned properly, the foreground 'live' objects cast shadows on the reflective screen that are perfectly masked by the object itself. The light from the projection is so weak on the foreground objects that the normal studio lighting will obscure it.

Piers Bizony's book "The Making of 2001" goes into great detail on front projection. Also look for John Brosnan's "Movie Magic" compilation, which has a chapter on Silent Running, IIRC.

 

[Jeff Ulmer]

Okay, that is beginning to make more sense - using shadows to create masks. That was the part that confused me, but I still need to see a diagram in order for this to be totally clear. I can see combining the image in camera (they used something like this on Zardoz as well, though not a projected image if I remember rightly), but how to not pick up unwanted areas from the projected image is what baffles me.

 

[Peter Apruzzese]

On Zardoz, they used a front surface mirror with the reflective surface *facing* the camera. It was positioned in such a way as to reflect a miniature model and make it appear to be in front of the camera. They would then scrape away the portions of the mirror that reflected images that they did not want and the camera would "shoot through" those sections to the live actors and scenery. Boorman also used this technique in Excalibur, but it's really an old trick dating back to silent films and magicians. Mario Bava used it as well.

I'm still not sure what you mean by "unwanted areas". The projection screen (and camera) would be sized properly so that no unwanted image was photographed. The only other unwanted image is that light from the projector that shines on the foreground objects. One thing I forgot to mention - this may be causing the confusion - is that the projection screen is a highly-reflective material (brighter than a highway marker, more like a cat's eye), so it reflects back only directly into the camera. Being so bright, it looks natural (unlike back-projection). The projector itslf doesn't have to be super bright, so the light from it that falls on the foreground can be covered up by lighting the foreground objects normally.

 

[Jeff Ulmer]

"It's a trick! A trick!" (Sorry, couldn't resist)

By "unwanted areas" I mean the parts of the projected image that should be covered by foreground objects.

As an example, lets say I was shooting a minature of the Eiffel Tower using a tracking shot. I want to have a spacescape in the background, which will be seen through all the steel girders. In a static shot using a matte painting, the girders area of the painting would normally be left empty, so the model would show through, a similar process would be used creating this optically, by making a hole that the model image sits in.

However, with a tracking shot, what is seen through the girders would change, so I am wondering what is done in order that the background image doesn't polute the foreground model, ie, show up on the girders. Did that make any more sense?

In Silent Running, Bruce Dern is shown at a window, which looks out onto space. He is in front of the window. The image of space is front projected, yet he can move around and not look like he has space on him.

 

[Peter Apruzzese]

"I could have shown you!" (I think that's the quote by Arthur Frain before he falls...)

Normally, you can't move the camera during a front projection shot. The projection shots in 2001 are static, for the most part. The ones where the camera moves were done with no foreground to worry about - he was using 8" x 10" transparencies of the African landscape. You'd have to have a rig that could move the camera and projector together in the same direction and you'd probably run into a problem with unsteadiness. Since the screen only reflects light directly in a straight line, if you only moved the camera by itself even slightly off-axis, the image would dim (like a rear projection television viewed from the side).

The shot you describe would be best done with a standard traveling matte (using a painting or transparency of the spacescape for the background) or even high-quality rear projection behind your model of the Tower.

EDIT - you just added that last part about Silent Running.
That's what I meant above about lighting the foreground. Picture the set completely dark. Put Dern in position. Turn on the front projector and view through the camera. You'd see the projection screen bright and clear and a faint image of Dern with the stars on him. You would then light Dern with key spotlights (that only shined on him and other foreground objects you want to see). Now, look again through the camera. The key lights on Dern are much brighter than the dim light from the projector and would effectively remove them from his image. It's like shining two different lights on the same object - the brighter light will be the one you see.

 

[Jeff Ulmer]

This is where the confusion comes in. In the Silent Running documentary, there are a couple of scenes they show where they specify they are using front projection: the window shot I just mentioned (I believe the camera is static, but Dern is moving in front of the window - he mentions looking at nothing while the image is compositied in-camera), other space shots where the camera dollies past the miniature with the space background, and all the shots inside the domes. I assume they rigged the projector and camera on a single dolly for those shots, but still don't see how they could do it as seamlessly as they did.

The sets just had white draping where the images would be located, which these days would be blue/green screen, and thereby auto-matte for a replacement image. This is what baffles me on the Silent Running stuff.

 

[Peter Apruzzese]

Jeff,

Unfortunately, my copy of the "Movie Magic" book is packed away somewhere, or I'd look up that chaper on Silent Running and see what it says. The shot of Dern you describe fills my scenario perfectly, those others do not. Unless, they weren't using the Scotch-Lite reflective screen for those sequences and were simply using traditional screens (the "white draping" you describe) and some type of planetarium projector or something.

 

[Jeff Ulmer]

That is what makes it confusing, they don't seem to be talking about projecting onto the draping. I'll have to watch the documentary again to see if I can figure anything out.

 

[John P Grosskopf]

Check out the documentary on the Superman the Movie DVD for everything you wanted to know about front projection, which was used extensively in Superman during flying sequences. front projection along with the then new "Zoptic" process (special lenses) allowed for front projection and zooms simultaneously.

 

[Seth Paxton]

It seems to me that this thread would be better served being in the Movies section to better field proper responses. I was lucky to stumble onto it over here.

It just seems to be about movie production much more than DVD software.

 

[Jeff Ulmer]

I had thought of posting it there, but it was sparked by an extra on a DVD, and from looking at the movies forum (which I never go to), all I saw were official threads on every movie playing in theatre. I suppose it wouldn't hurt to have it there...