T436 Fall 2012 - Week 8

Readings: TBA

 

Agenda:

• Reality check
• Production update & meeting

Reality Check

• Everyone should update their wekely blog / journal.
• When a project has wrapped or finished Producers, Directors, DPs, Gaffers and Audio Engineers submit additional Production Packets. Look here if you need to find out what goes in the Production Reports .

 

Tech Issues (cont.)

Lighting & Color

Setting up a Color Monitor

http://www.videouniversity.com/articles/color-bars-and-how-to-use-em

Note that standard SMPTE bars will appear slightly different on an HD monitor compared to the downconverted image on an NTSC monitor. On an NTSC monitor the two small grayscale stripes will blend in as they are 3.5 and 7.5 IRE. Since HD monitors show us digital (0 IRE black level) we should be able to see the difference between the two.

Lighting Issues

While both tungsten & discharge lights run on alternating current, only the HMI and fluorescent fixtures will cause flicker problems.

All HMIs and fluorescents flicker- it’s just not noticeable to the human eye.
If the frame rate of the flicker is timed in sync with the camera (shooting NTSC in the US under fluorescent fixtures operating at 60 Hz), then at least the output is consistent.

But if you go to Europe with an NTSC camera (60 Hz field rate) and shoot under their fluorescent figures operating at 50 Hz, the relationship of the shutter and light output will fluctuate.

An HMI light that works fine with 29.97 (NTSC) might flicker when shooting at 24p. Most have switches that let you vary the crystal controlling the frequency.

Filming Monitors

CRT computer monitors will often roll since their scan rate is not necessarily 60 Hz. (LCD monitors have more persistence, so the roll is not noticeable.)

Professional video cameras have a variable scan or clear scan mode. This allows the operator to reduce the frequency of the sampling by fractional amounts so the roll can be minimized.

Similarly, NTSC TV monitors shot with film (or at 24p) will exhibit similar rolling.

Usually TV monitors will appear brighter and bluer when captured on video. While it’s sometimes possible to adjust the hue and brightness to make them more acceptable, often an orange gel is used to both warm the color and stop the brightness down.

Keys

Luminance keys – uses brightness (luminance)
Chroma keys – uses color
Difference keys – uses software to figure out the difference by before and after shots

Lighting for chromakeys

• Must be uniform
• Must be shot clean (no diffusion filters, etc.)
• Backlights often used with opposite color from key to help reduce spill and increase keying ability

 

Controlling light

(review ways to control lighting)

Strobes

Are sometime used in cinematography and provide the following benefits:

• Light cooler (they produce much less heat)
• Can produce sharper images (even if the camera is running at 24 fps, the strobe can give it a practical exposure of 1/100,000 of a second
• Provide enough lighting for high-speed photography

 

The exposure must be carefully calculated.

High Speed Photography

The exposure must also be carefully considered. A faster shutter speed requires you to change accordingly on your light meter. You can plug the frame rate into your light meter or do the math yourself.

Modulation Transfer Function (MTF)

The measure of a system to produce fine detail. Lenses often have an MTF figure.

Special Effects

• Smoke – Real smoke is hazardous to your health. Brown talks about “cracker smoke” produced by forcing air through fine oil.
• TV & fireplace “flicker” – Can use a flicker box
• Day for night – Sometime shot at midday to reduce shadows. Can use filters.
• Moonlight – Generally blue
• Water – Use the real thing when possible (a shallow pan with a PA disturbing it)
• Rain – Should be backlit. Need to protect gear.
• Time lapse – Light can vary immensely. Can be done with still cameras. The Corpse Bride was shot with a Canon digital still SLR.
• Time slicing (many nice pictures of rigs in book)

 

 

 

 

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