3D

[Chie]

I've seen a few 3D documentary films on my visits to the national museum of photography, film and TV in Bradford. They have an huge IMAX screen which you watch through tinted glasses - no need to have different colours and the 3D effect is spot on. I think the key thing is that the screen is curved, as opposed to a normal cinema screen which is flat and two-dimensional. So cinemas could gradually replace their flat screens with curved IMAX ones and then it would be perfect.

[Gavin Scott]

I've seen a few 3D documentary films on my visits to the national museum of photography, film and TV in Bradford. They have an huge IMAX screen which you watch through tinted glasses - no need to have different colours and the 3D effect is spot on. I think the key thing is that the screen is curved, as opposed to a normal cinema screen which is flat and two-dimensional. So cinemas could gradually replace their flat screens with curved IMAX ones and then it would be perfect.

Not so sure about curved screens. Maybe. There's a point where having to turn your neck so see around is a little more effort than an audience want, where a well composed large picture allows you to zone straight ahead and be absorbed.

That's what I tend to think, anyway.

The tinted specs you speak of are made with polarising filter, but its expensive stuff.

To give you an idea, 8" x 8" sheets of the same thing used for lighting retails at £49 +vat. That's not so many pairs of glasses (2" x 1" per eye x 2).

People nick them after 3D shows - there's a constant stream of replacements being delivered, that much I know.

[Sput]

Why do they polarise lights gav? Reflection in photography or something?

[Gavin Scott]

Why do they polarise lights gav? Reflection in photography or something?

Yes, just so. Where you're studio based, polarising the light before it lands on reflective surfaces (such as car windscreens or anything similarly shiny), stops the waves bouncing back towards the camera causing glare, with a bit of adjustment to the direction of the filter.

They also use polarising filters over camera lenses, but these are optical grade and are many many times more expensive than non-optically perfect lighting filter. That's useful for shooting through glass, such as windows, by killing refection of the sky.

You can also combine the two.

TV studios with windows visible (behind the talent) often have polarising filter on them, with a polarising filter on the camera lens. By adjusting the rotation of the filter on the camera lens they can effectively reduce the amount of light that comes through the windows (as far as the camera can see it anyway), and create a balance to the exterior and interior.

[Chie]

Is that the same thing that causes lights in the background of a shot to become blurred, like this? I've always wondered about that because they're not always circles - I've seen triangles, pentagons, hexagons, squares, and on one 80s film, squares that have a single rounded corner. How are the different shapes achieved?

[Gavin Scott]

Is that the same thing that causes lights in the background of a shot to become blurred, like this? I've always wondered about that because they're not always circles - I've seen triangles, pentagons, hexagons, squares, and on one 80s film, squares that have a single rounded corner. How are the different shapes achieved?

In the image you linked to, that is just the background out-of-focus - but that leads on to things like "depth of field", as in, the amount of distance between the nearest and furthest objects that appear in acceptably sharp focus as seen by a camera lens.

This is adjustable by the cameraman so the same shot can look like either of the images shown below:



However, you're quite right, there are "diffraction" filters which can be put over the lens which create streaks of light - sometimes in a criss-cross shape. Think Top of the Pops in the 70s, 80s and 90s. There's a few variations of this, which it sounds like you've seen.

In the cinema you'll often see circles of light emanating from a light source. This isn't from the use of a filter, rather its because of the lack of "masking". Usually great care is taken (using black cloth pieces called "flags" positioned between lights and camera) to stop strong points of light getting directly into the lens as it will cause a flare of light as it bounces around inside the optics of the camera.

This is particularly noticeable in the new Star Trek movie (its deliberate - part of the look of the film), but you might notice these circles are more oval shaped. That has to do with the fact that all camera lenses are circular, but the picture shape ultimately comes out as a wide rectangle - so the circles of light are "squashed".

But that's another discussion..!

[Sput]

*Awards Gav some Sput Science Points*

[Gavin Scott]

*Awards Gav some Sput Science Points*

Yes, umm... I'd like to cash these in. How many for that colour TV?

That many?

Oh. Do you have any gonks with tartan hats?

[nidave]

There is no benefit to me in 3D - I am red green colour blind and I have monocular (not sure if that's the right spelling but it will do) vision.

I have been to the iMax 3D and saw monsters V aliens - There were 3 things that I thought were in proper 3D but when I recently watched it on a DVD I had the same effect from an normal TV screen. I think this is how I represent things in a 3D space (as if I am looking at a flat TV ). My brain must fill in the gaps from my vision. I am not sure how to explain it as I have been like that all my life - I can switch between eyes at will.

[Pete]

on a slightly related note, I happen to see reddish vision in my right eye and bluer if my left (this has occurred ever since right eye was hit with a cricket ball when I was about 8). They seem to cancel each other out in normal vision however would this affect my 3D specs vision?

[Gavin Scott]

on a slightly related note, I happen to see reddish vision in my right eye and bluer if my left (this has occurred ever since right eye was hit with a cricket ball when I was about 8). They seem to cancel each other out in normal vision however would this affect my 3D specs vision?

It might.

If you're very lucky you won't need them at all.