Using a mirror for reflections... need suggestion.

[ashleylynch]

Greetings,

I'm in prep on a short film where the location has a large mirror against one wall. I was intending to cover it in a matte and mount a framework around it to turn it into an exterior window in post.

But now I suddenly got the idea that maybe it would be better to leave the mirror uncovered. Since I'm going to matte it out anyways and it will ostencibly be a square geometric shape, perhaps it would be in my best interest to just shoot the mirror so I can use the reflection as part of the reflective layer for the glass window in post. The only downside to this I see would be there may be some shots that require some rotoscoping since I can't perform a chroma key composite.

I haven't done tests on this yet, but I'm wondering if more experienced people think this is a potentially good or bad idea.

Ashley

[zoostory]

It just depends on how much Roto and tracking you will have. If people are dancing with long curly hair in front of that thing, you probably want to green it out. Likewise, if you are in so tight on some shots that it's all mirror, unless you find some specs of dirt to track on to, you're in trouble for a 2D and/or a 3D track. If you're out wide and see the corners, you'll be fine.

Also, remember, a mirror is (more or less) a 100% reflective surface, whereas a window made of glass is a more complex surface with some reflection, but also refraction of light coming in from the outside (due to the imperfections in the glass). There's always some atmosphere that gets caught in there, occluding some of your reflection. Not to mention if it's dirty glass you get some light pick up and occlusion on that dirt.

You could always put some green screen in front of the mirror, then get some glass cut to that size and put that in front of the green screen, that'll get you some reflective elements as well as the shot at a key.

Oh, and watch for camera reflections

[aaronber]

I agree, it completely depends on how much work you want to do, what your budget is, and what the shots are.

Another thing to remember is that a glass surface would reflect a small portion of the light back to your camera. Effectively your reflection would be way underexposed. To the point sometimes you can see lighting fixtures and stuff like that in a window reflection that would be blown out in a mirror reflection so make sure there isn't anything in the mirror that would blow out so you can drop the exposure in your comp.

It could be a great idea, but do some tests (even if it is you against your bathroom mirror, of course the closer your test to what is actually going to be shot the better) and plan it out before you shoot it with actors.