HMI

HMI units, also known as Hydrargyrum medium-arc iodide, are the trademark name of Osram's metal-halide gas discharge medium arc-length lamp. Hydrargyrum is Latin for "liquid silver", abbreviated to Hg.

Unlike incandescent- lighting units, can output closer to 6000K, which is similar to the color of light emitted by the sun. Sun-like light is extremely important when trying to mimic sunlight, or to complement sunlight when shooting outside.

Note that HMI lamps should only be operated by professionals, as their ignition voltage can reach up to 70,000 V, and their ultra- violet light can cause retinal damage and severe burns without the UV safety glass cover.

Gaffer Tape

Much like the Force in Star Wars, Gaffer Tape has a light side and a dark side, and it binds the universe together. Gaffer Tape, not to be confused with Duct Tape, is a heavy cloth pressure sensitive tape. The adhesive is rubber based, which makes it more resistant to heat, and much easier to remove from the surface it has been applied to. And once you see it used on set, you'll be amazed how many applications it's used for! Again, not to be confused with Duct Tape - which is great, in some circles, isn't nearly as awesome as Gaffer Tape!

Gaffer tape is used by all departments, even though it's named for the head electrician. Camera, grip, production, even make-up and wardrobe use gaffer tape! Common uses are to secure cables to prevent tripping or to hide cables from the camera, a quick label maker, to mark focus points or ‘spikes’ noted for talent blocking, holding props or paper, and of course to repair broken things. There are as many colors of gaffer tape as colors in the world, but the most common is matte black, as it tends to not reflect light.

Extras

Think of all the people you see in the background at the diner in Seinfeld, Cheers, or even the Stormtroopers in Star Wars.

They say nothing, or pantomime gibberish to each other to make it look like they’re having a conversation.

Famous Extra Fact: James Michael Tyler was a ‘background’ actor in NBC‘s Friend’s café, Central Perk, when one day in the second season he was given a line, and suddenly he was the character Gunther on the show... for ten seasons!

The Assistant Director usually corrals and directs the background actors.

If you're interested in becoming an extra, there are many websites (try this one!) and resources out there. Remember that this is a profession, and the days can often be long, and in the elements. It's not for tourists. And also note that asking for autographs is extremely unprofessional and might get you tossed off the set.

D.P. - Director of Photography

Maybe you've heard the title Cinematographer before? Or been on set and someone keeps talking about the "DP" and you've always wondered, who's that person? What does a DP do? And why are they so important?

The D.P. or Director of Photography has many rolls and supervises many hats. Many of these professionals have worked their way up to be the head of the camera, grip and electric departments - as all these departments report to the DP before they report to the Director.

On some shoots, the DP is in charge of even more than just the camera placement and what's in the frame. On other shoots, he or she may be a lighting director in addition to making choices about costumes, make-up and wardrobe - and why a pin-stripe suit will Moiré on the screen. 

The DP also looks after the footage, often making choices in post-production and editing regarding the color grading of the film or footage, color correction, and helping with the special effects.