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Friday, September 26, 2014

••◊ We Might Need A Bigger Light...How To Know?

I was talking with a director about a moonlit scene along a beach here in Southern California.  He said the producer wanted a scene where he was walking down the beach after dark.  The question was how to light it and how much would it cost?  That's what leading me to this particular blog post this week.

First, some basics.  Light from a light fixture falls off in as the inverse squared.  Confused?  Let me explain.  Let's say you are standing 10 feet from a standard Arri Fresnel lamp and you take a meter reading.  The meter says T5.6 (no f-stops!...we're filmmakers here, not still photographers).  Then you move to 20 feet from the lamp.  The meter should now say T2.8.  The reason?  You moved 2x the distance from the lamp therefore the comparative amount of light is 1/(2squared)=1/4.  That's 2 stops less light.  Now let's say you moved out to 40 feet (2x again) from the lamp and take another reading.  The light meter should read T1.4, i.e. 2 stops less again.  The main point I want you to take away is that every time you double your distance from the lamp you have 2 stops less light. 

The other point is that as you get further and further from the lamp the light fall off becomes more and more gradual.  Just look at the way the graph is trending.  Think about the sun and moon.  It's a large lamp a long, long distance away.  Have you ever noticed an exposure difference by moving 10, 50, or 100 feet back from the sun?  How about a mile?

The other basic concept for any cinematographer is how to calculate what size of lamp you need give the essential exposure parameters of ISO, shutter speed, and lens T-stop.  I've wrote about this before, but here is the summary again...

foot-candles = 25 x (T-stop)^2 / (ISO * shutter time)

A quick way to calculate the required lamp size is to remember that T2.8 at ISO 100 and 1/48th shutter (i.e. 180-degree shutter at 24p) takes 100 foot-candles.  You can see how to quickly do the math in your head from there if you know the formula.

So back to the problem at hand...

I figured along this particular beach we want to light about 1/10th mile (528 ft) of 100 foot wide beach to sell the light as moonlight.  As a starting point I'm going to assume a modern camera with ISO 800, a T2.8 aperture, and 24p.  Moonlight is never fully lit like sunlight, so let's assume that the person is exposed 2 stops under.  This means I need enough light to properly exposure at T1.4, i.e. 2 stops less than T2.8.

This gives the following table of required foot-candles from our fixture...

Distance (feet)      T-Stop      Foot-Candles (assume ISO 800, 1/48th shutter, T1.4)
528                        T1.4         3.125
264                        T2.8         12.5
132                        T5.6         50
66                          T11          200
33                          T22          800
16.5                       T45          3200
8.25                       T90          12800

Now let's look at the photometric chart for a Mole-Richardson 4k HMI PAR fixture.

The medium setting on the beam focus seems to give us just over 3200 foot-candles at 20 feet.  This roughly matches our requirement at 16.5 feet.  Also the narrow beam focus greatly increases the output, however you need to keep in mind that we need to illuminate a 100 foot wide section of beach so the background doesn't quickly go to black and ruin the effect.

What this doesn't take into account is atmospheric haze, the light position, and gels.  There's a diffusion effect from the atmosphere, so you may want to consider moving up to a 6k PAR from a production margin standpoint.  I want the light to be about 528 feet back from the subject we are lighting.  The light will require a crane and generator, which needs to be parked somewhere and you won't necessarily have a spot exactly 528 feet away to park!  Also, moonlight tends to be very blue so you may want to gel the light with a CTB of some sort.  That will significantly drop the light output.  You may then want a 10k or 12k PAR. 

The main point of this exercise is to show why you may want to consider a "big" light sometimes.  Cinematographers commonly use 12k and 18k HMI lights and it's not because they want to be Hollywood fancy-pants blowing through those multi-million dollar budgets.  Sometimes you just need a big light, especially when you need even lighting over a large production set.  A "Wendy" light is a good example.

If you have questions, feel free to leave a comment.

Saturday, September 13, 2014

••◊ Random Travel Photos From Boise

I spent the last few days in Boise and took some obligatory pictures to share on my blog.  Meet the new state mascot, Darth Tater.  "May The Starch Be With You" seems like a true stretch, but Idaho isn't known as a center of fashion design and marketing.  There is a "force" after eating starchy foods, but it's not a force most people want to let loose in public places.

The hotel I stayed at was well decorated, so I took a few photos while waiting for someone in the lobby.

The real reason I look forward to Boise trips are the walks along the river.  Boise has a nice trail going east and west along the north bank of the Boise River.  The usual assortment of dog walkers and runners enjoy a morning stroll...then there's me brandishing a camera and trying to make it clear that I'm not trying to take their picture. It's interesting to walk along the river because you quickly realize that all greenery 40 or more feet from the river is artificially supported with landscape irrigation, just like in San Diego.  Boise is what I would describe as arid prairie; mostly brown year round.

Two years ago I was on the same walk and came across this wagon in a field.  This time the wagon was at the end of the newly paved section of the trail.  Last time I was there the weather was cloudy and dismal winter blue, making for miserable pictures.  This time I took advantage of the bright summer lighting.


Then there's the obligatory pictures of the river itself.

On the way back we had a stop over in Las Vegas for an hour.  After being in Boise I was looking around the airport and realizing what a culture shock this transition was.  I was traveling from ultra conservative quiet Idaho where the airport is considered crowded with 10 people in the TSA line to sin city.  When I first got off the plane I wondered why are all these womens' skirts so short?  What is up with all this gambling and why is the airport so busy?  Leopard print...really?

The nice thing was that the flight home was quiet and the view over the southern California desert was pretty at night.  I wished I could have caught it better with the camera I had.  The light on the horizon created this dappled golden landscape with hazy blue shadows behind the hills.  By the time the landscape was at its most spectacular there just wasn't enough light to take a picture with the point and shoot I had with me.  It's better to experience in person anyway.

Monday, September 8, 2014

••◊ Diffusion Materials for Film and Video Lighting

This week's entry comes from a reclined position on the couch.  I became ill after a music video shoot on Saturday and since then my life has consisted of a series of positional changes while sitting or laying on the couch.  I'm trying to get work done in between naps.  So whatever entry I did today had to be within arm's reach of the couch.

Last week I grabbed some swatch book samples for Lee and Rosco filter products from my local production supply house.  If you don't have these I would recommend that you get them.  The swatches are free and help you choose filter colors and diffusion material without having to just buy a bunch of stuff and try it.  The reason I grabbed the swatch books is that I couldn't find any good reading material on the Internet about standard film lighting diffusion material - i.e. 216, 250, opal, soft frost, grid cloth...etc.  Most professionals seem to have their selection of what diffusion material to use in which situation and it made me feel like I needed to do a bit of self education.

First, I want to say that I come into this study with no particular preference for brand.  Despite similar naming conventions the brands of diffusion and filters have some very significant differences.  It was sort of like when I had a sheet of full CTB from Rosco and went into the shop looking for more.  They only had Lee, which looked quite a bit different!  That taught me to stick with one brand for the particular product I was looking for.  The same can be said of diffusion.

So let's start looking at the diffusion materials, shall we?  216 is the catch all, default diffusion material.  I once read a recommendation from an ASC member that said that if you don't know what you want, start with 216, then decide if you want more or less diffusion.  While Rosco claims a "minimal" color shift, Lee actually rates the color temperature of the material at 6774K, which means it will add blue to your lighting.  Also, if you look at the pictures you'll see that Lee is more dense than Rosco (this isn't a good/bad judgment).  The density is supposed to be similar to tracing paper, but tough enough to withstand film production. 

Another common type of diffusion material is grid cloth.  Grid cloth is known for creating a mixture of diffusion and directional light.  As you can see in the photos below the cloth is a woven grid which heavily diffuses light, along with a less dense base which allows some directionality.  I often hear about other DP's using this as a close proximity diffusion material to emulate diffuse daylight.  One thing that I noticed when reviewing the two swatches is that there is a color temperature difference between the two materials.  The Lee fabric is slighting cooler and the Rosco material is slightly warmer.  You may or may not be able to see the difference on your screen, so I would recommend reviewing the swatches in real life.

Grid cloth comes in a few densities.  Another common fabric is light grid cloth.  As the name implies, it's a lighter density than full grid cloth.  Here the Rosco brand is a bit more diffuse than Lee, however both maintain about the same grid geometry.

Speaking of density, a common use of grid cloth is diffusing light outdoors.  The problem is that these industrial fabrics can be quite tough and stiff, so they make noise that will drive your sound person nuts in the wind.  For these situations the vendors make silent grid cloth.  It tends to be a bit more dense than regular grid cloth, but as you'll see in the photos it's also much more pliable.  So when silent grid cloth flaps in the wind it doesn't make as much noise.

A few DP's I know of like to use either quarter grid cloth or half-soft frost for overhead diffusion outdoors.  I think it depends on the amount of "raccoon eye" correction you're going for, because sometimes I want a full grid or a silk.  The photos below show that Rosco is a bit more dense and has a larger grid pattern than Lee, so the diffusion is going to have a different effect between brands.  The dot pattern on half-soft frost is also a bit different, so the two brands have slightly different diffusion characteristics (but I probably wouldn't be able to notice a difference). 


I realize this can all be a bit confusing.  You're probably thinking what I was thinking at first - "OK, what do I use?"  That just has to come from experience and working with a great gaffer.  My best advice is to follow what a wise DP once told me - "start with 216 and figure out if you need more or less diffusion."

One thing I've been meaning to do lately is go on another expedition to the fabric store and figure out which of these diffusion materials I can closely approximate with regular fabric.  "Rags", as the industry calls them, can be quite expensive.  Sometimes you can get something close enough for $10 at a fabric store as long as it doesn't have to be flame retardant or made for the rigors of daily production.

Monday, September 1, 2014

••◊ "It'll Be Great For Your Portfolio!"

This week I was reminded of one of the common annoyances of being a no-name in video production.  I received an email that we pretty much all have in the past saying, "such-and-such company/organization needs a video done.  They don't have a budget, but it'll be great for your portfolio!"  I usually equate these messages with the calls I receive from phone solicitors every week.

First, do you know what I do?  I don't do event videography unless it's an organization I'm involved with or have a passion about.  As a DP I do photography for motion pictures.  I direct a crew to light a scene, frame the shot, plan equipment needs, and move a camera.  That's what I do.  If they can't afford to hire me that also means they can't afford to hire my AC, provide catering, a camera rental, as well as grip equipment.  Even most of the videographers I know in town need to have the cost of their camera equipment amortized over the year, so they aren't likely to bring their gear to a freebie shoot.

Then you get the statement, "it'll be great exposure!"  Do you really know who I want to be exposed to?  Do I want to be exposed to more NPO's that want free work done?  How will I be credited such that everyone watching the video will know?  Who is doing the edit and color grade such that my footage won't get screwed up in post and I'll look bad?  Unfortunately I've learned this the hard way through the last few years.  There are certain people who you don't want to work with because you know their standards for "good enough" will make my work look like an unprofessional amateur.  There are also projects where I requested to have my name removed from the credits in the end.  Doing these type of projects doesn't get you very far as a director.  Not all exposure is good exposure.

Now there is a time and place for the infamous "portfolio" and "exposure" keywords.  For instance I shot a promo for Aerial Mob earlier this year.  I knew the director and crew and the level of work they wanted to achieve.  I was working with a prototype camera and stabilization system which I knew would get attention on the Internet - which it did.  The video also ended up as a demo at NAB in 2014 playing at the Tiffen booth. 

I like freebie work when I know I'm going to learn something; for instance, working with an ASC member as I did last summer on a documentary or on the Aerial Mob shoot where we were working with the prototype Panasonic GH4 and the Movi-like handheld stabilizer.  Learning opportunities put a few more useful bullets in my back pocket when difficult situations arise.  I love freebie shoots for learning new cameras.  That's how I learned how to use the Red Epic, C100, FS-700, and most of the cameras I've used.

So before someone comes begging to me for free camera work they need to look at it from my perspective.  Does the production really offer anything?  My colleague Angelina has made the proclamation that she won't work on free projects unless it's a passion project.  The trick with marketing free projects is how you sell the "passion" part.