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Old 11-14-2009, 08:16 PM   #21
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Wow! Eileen, excellent post, and thanks for all that info. I can't wait to get some free time and start sifting through it.
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Old 11-15-2009, 06:25 PM   #22
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Wow! Eileen, excellent post, and thanks for all that info. I can't wait to get some free time and start sifting through it.
Thanks Peter. I strongly encourage anyone using HMIs on portable generators read the article. It is full of useful information that systematically refutes a lot the conventional wisdom I have read in forums. For example, you are better served by using the older magnetic ballasts on an inverter generator like the Honda EU6500is over non-PFC electronic ballasts. As Guy explains in his article, when electronic square wave HMI ballasts came on the market, they were at first thought to be the solution to all the problems inherent in running HMI lights on small portable generators. By eliminating the flicker problem associated with magnetic ballasts, they also eliminated the need for the expensive and ultimately unreliable AC governors required for flicker free filming with magnetic HMI ballasts and portable gas generators.

Since they are not frequency dependent, it was thought at first that electronic square wave ballasts would operate HMIs more reliably on small portable generators – even those without frequency governors. For this reason, as soon as electronic square wave ballasts appeared on the market, many lighting rental houses replaced the more expensive crystal governed portable generators with less expensive non-synchronous portable generators. The theory was that an electronic square wave ballast would operate reliably on a non governed generator and allow filming at any frame rate, where as a magnetic HMI ballast operating on an unreliably AC governed generator allowed filming only at permitted frame rates.

In practice, electronic square wave ballasts turned out to be a mixed blessing. Part of the problem with operating electronic HMI ballasts on portable gas generators in the past has to do with the purity of the power waveform they generate. With an applied voltage waveform distortion of upwards of 19.5%, conventional generators do not interact well with the leading power factor (current leads voltage) of the capacitive reactance created by electronic square wave HMI ballasts. The net result is harmonic currents are thrown back into the power stream, which results in a further degradation of the voltage waveform and ultimately to equipment failure or damage (for the reasons discussed in my previous post.)

The oscilloscope shots of the power waveforms below is from the article mentioned above and is typical of what results from the operation of a 1200W HMI with non-power factor corrected ballast on grid power (left), on a conventional generator (middle), and inverter generator (right.) The adverse effects of the harmonic noise generated by non-PFC electronic ballasts and exhibited here in the middle shot, can take the form of overheating and failing equipment, circuit breaker trips, excessive current on the neutral wire, and instability of the generator’s voltage and frequency. Harmonic noise of this magnitude can also damage HD digital cinema production equipment, create ground loops, and possibly create radio frequency (RF) interference.



As is evident in the oscilloscope shots below of a 1200W magnetic HMI ballasts on grid power, on power generated by a conventional Generator (Honda EX5500), and power generated by an inverter generator (Honda EU6500is), the lagging power factor caused by the inductive reactance of magnetic ballasts has by comparison only a moderately adverse effect on the power waveform. Outside of causing a voltage spike in the inverter power, magnetic ballasts actually show a positive effect on the already distorted power waveform of the Honda EX5500 conventional generator. For this reason magnetic ballasts work better on conventional generators with frequency governors than do non-PFC electronic square wave HMI ballasts.



These oscilloscope shots show that if you don’t have access to the newest PFC electronic ballasts, the older magnetic ballasts are in fact cleaner running on portable gas generators than non-PFC electronic ballasts. And, where inverter generators like the Honda EU6500is do not require crystal governors to run at precisely 60Hz, you can operate magnetic HMI ballasts reliably on them. In addition, the smaller magnetic ballasts (575-2500W) offer the distinct advantage of being less expensive and draw less power (once they have come up to speed) than the commonly available non-PFC electronic equivalents (13.5A versus 19A for a 1.2kw.)

Of course there are downsides to using magnetic ballasts. One down side is that you are restricted to using only the safe frame rates and shutter angles. But when you consider that every film made before the early 1990s was made this way, you realize it is not such a limitation. Another downside to magnetic ballasts is that you can’t load the generator to full capacity because you must leave “head room” for their higher front end striking load. When choosing HMIs to run off portable generators, bear in mind that a magnetic ballasts draws more current during the striking phase and then they “settle down” and require less power to maintain the HMI Arc. By contrast, an electronic ballasts “ramps up”. That is, its’ current draw gradually builds until it “tops off.”

For example, even though a 2.5 magnetic ballast draws approximately 26 amps you will not be able to run it reliably on the 30A/120V twist-lock receptacle on the generator’s power panel. As mentioned above, magnetic ballasts have a high front end striking load. For this reason, you must always leave “head room” on the generator for the strike. But, even though the twist-lock receptacle is rated for 30 Amps conventional 6500W generators are only capable of sustaining a peak load of 27.5 Amps per leg for a short period of time. Their continuous load capacity (more than 30 minutes) is 23 Amps per leg. And if there is any line loss from a long cable run the draw of a 2.5 magnetic ballast will climb to upward of 30 Amps. To make matters worse, the lagging power factor caused by the inductive reactance of the magnetic ballast kicking harmonic currents back into the power stream causes spikes in the supply voltage that can cause erratic tripping of the breakers on the generator or ballast. (for a more detailed explanation of why that is I, again, suggest you read SL&G’s newsletter article.) In my experience the load of a 2.5kw magnetic ballast is too near the operating threshold of a 6500W generator for it to operate reliably.

The only sure way to power a 120V 2.5kw (or even a 4kw) HMI magnetic ballast on a portable gas generator is from its 240V circuit through a 240v-to-120v step down transformer like the one SL&G manufactures for their modified Honda EU6500is. SL&G’s 60A Full Power Transformer/Distro will step down the 240V output of the generator to a single 60A 120V circuit that is capable of accommodating the high front end striking load, and even the voltage spikes, of either a 2.5kw or 4kw magnetic ballast at 120V.

Eileen Ryan, Gaffer, Boston
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Old 09-16-2010, 01:13 AM   #23
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The Arri Lighting Handbook from the first link failed, but you can download it by clicking this: http://www.videotexsystems.com/files...ok_english.pdf

A great learning site with lots of lighting diagrams and the reasons why lighting setups are chosen is Walter Graff's instructions at http://www.bluesky-web.com/index-5.html There is lots of good general information as well and many interview setups are broken down.

Graff also has good instructions on turning inexpensive, battery operated florescent lights into great tools. His "What's In My Bag" article was a nice article in DV magazine and talks about the relatively low-cost instruments he uses. I think it would be a great kit to emulate and with a few extras, might be all the kit you need for practice and a lot of practical work. You might want to rent if you need much more. Also, Graff goes beyond 3 point lighting and explains why not to use it.

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Old 09-16-2010, 01:50 PM   #24
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That Arri book is a great read even if none of the examples look natural, but is of little modern application to the Indie filmmaker using low-light digital cameras in real locations.

I have only really found one book in which a filmmaker briefly talks about the modern application to lighting and that was the Mike Figgis book, where on the whole he talks about using the natural light of a location, then if needed a few cheap lights, and at best a couple of professional lights if really needed.

I often think about at film school a lecture talking about how amazing a cafe scene had this lighting that looked so nature, and it was amazing considering the scene was of a cafe with a huge glass front shot to look like daylight which is actually some dark sound stage in a random studio lot, I remember thinking that was a lot of skill and craft involved in that and also many hours of hard work, and got saddened that on my budget I'd never be able to get a scene to look that nice, unless I just took a camera to a cafe - which isn't too hard, I'd have issues in controlling the noise and sound but be able to shoot an endless number takes with the help of the cafe.

It is wise to learn the craft, and if you are working in a studio work hard to make it look as natural as possible, yet on location all those rules have changed and you start from a position of what is the natural lighting of this scene and does it need enhancing, and usually that involves a cheap fill light and a filter over the windows at the most.
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Old 09-16-2010, 03:06 PM   #25
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Granty,

I thought it odd that the Arri book was mostly portrait or single person interview setups. When I think of Arri and their history of compact and handheld cameras and use in capturing news footage. You'd think a couple examples would be of people moving within a set, at least.

I'll have to pick up the Figgis book. Sounds good.

I always wondered why there was no Mole or Arri light kit produced for a student budget. Maybe something in the $500 range.

Walter Graff talks about being trained to light and see by old time guys who dated back to studio pictures in the 40s and who could light a room with just a light or two. And while he covers a ton of interview stuff, I like that he isn't averse to using more affordable lighting, like Lowels, and emphasized a lot of punch in a tight, sturdy, efficient kit.

I relate to your sentiment about enhancing what's already there. By circumstance, that's what I've had to do. However, I've had a lot of fun shooting run and gun and chasing sunlight to get the day done.
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Old 09-16-2010, 03:22 PM   #26
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Quote:
Originally Posted by Granty View Post
That Arri book is a great read even if none of the examples look natural, but is of little modern application to the Indie filmmaker using low-light digital cameras in real locations.

I have only really found one book in which a filmmaker briefly talks about the modern application to lighting and that was the Mike Figgis book, where on the whole he talks about using the natural light of a location, then if needed a few cheap lights, and at best a couple of professional lights if really needed.

I often think about at film school a lecture talking about how amazing a cafe scene had this lighting that looked so nature, and it was amazing considering the scene was of a cafe with a huge glass front shot to look like daylight which is actually some dark sound stage in a random studio lot, I remember thinking that was a lot of skill and craft involved in that and also many hours of hard work, and got saddened that on my budget I'd never be able to get a scene to look that nice, unless I just took a camera to a cafe - which isn't too hard, I'd have issues in controlling the noise and sound but be able to shoot an endless number takes with the help of the cafe.

It is wise to learn the craft, and if you are working in a studio work hard to make it look as natural as possible, yet on location all those rules have changed and you start from a position of what is the natural lighting of this scene and does it need enhancing, and usually that involves a cheap fill light and a filter over the windows at the most.
The problem with naturally lit locations, as David Mullen pointed out, is that the light is constantly changing. You may be filming a scene with a timeline of minutes over a period of many hours. To maintain the illusion you have to continually adjust lighting of the scene so as to maintain a constant look. By comparison a stage lighting setup in a controlled environment is a piece of cake.
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Old 09-16-2010, 05:16 PM   #27
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The problem with naturally lit locations, as David Mullen pointed out, is that the light is constantly changing. You may be filming a scene with a timeline of minutes over a period of many hours. To maintain the illusion you have to continually adjust lighting of the scene so as to maintain a constant look. By comparison a stage lighting setup in a controlled environment is a piece of cake.
Yet I presume a large stage, with a solid fully furnished set and a huge rented lighting rig is not going to be a solution within the budget of most filmmakers in the market for a Scarlet, and it is far from a piece of cake to setup and light such a stage, taking days of hard work, weeks of preparation and a whole range of skills.

As a scene is going to take hours to shoot it would be far easier to shoot in a location that you have access to a the same time of day over a period of a few days, and keep a careful eye on the weather forecast to slot it into a time when the forecast doesn't appear to be too changeable.

Also when shooting in say a hotel room then the light is very controllable, as is a street scene at night, small rooms with a single window during the day are also very controllable, if you have just one powerful light setup to shine into the room from the window.

Controlling light is important, yet a minor consideration compared to staying within an extremely limited budget. Yet if budget is a minor concern then don't be waiting for a Scarlet, go hire all the equipment that you need, build a whole bunch of elaborate sets with expensive lighting setups, and while you are at it give your script to the agents of Hollywood's A list actors - piece of cake for $50m.

That is one thing that is nice about that Figgis book, he takes it to the basics of what a person needs to make a film and is really comes down to 3 basic components, maybe a story is a good thing to have, some actors may be needed to play the parts in that story, and a camera is a must have, any camera will do - everything less is people just screwing themselves over because "The greatest enemy of a good plan is the dream of a perfect plan."
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Old 09-25-2010, 02:22 PM   #28
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The cheapest and most important aspect of lighting that is not mentioned enough is flags and things of that ilk. You can use softened work lights if you have flags to control the light. Like Granty says its more about controlling the light, finding light sources is not that difficult
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Old 10-15-2010, 12:35 PM   #29
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Hey everyone,

I am pleased to announce that Harry Box, author of “The Set Lighting Technician’s Handbook” has cited my work on the use of portable gas generators in the just released Fourth Edition of the handbook. In addition, he has established a link from the companion website for the Fourth Edition of the Handbook, called “Box Book Extras,” to a company news letter article I wrote on the use portable gas generators in motion picture production.


If you haven't yet read the article, or looked at it in a while, it is worth reading. I have greatly expanded it to be the definitive resource on portable power generation for motion picture production. Of the article Harry Box states:

"Great work!... this is the kind of thing I think very few technician's ever get to see, and as a result many people have absolutely no idea why things stop working."

"Following the prescriptions contained in this article enables the operation of bigger lights, or more smaller lights, on portable generators than has ever been possible before."


The “Box Book Extras,” site is also worth checking out because it includes other source material used for the handbook, articles by Harry Box published in other periodicals, related websites, a list of production oriented i-phone apps, as well as more in depth discussion of topics touched upon in the handbook. You can log onto the Box Book Extras site at http://booksite.focalpress.com/box/setlighting/ with our pass-code "setlighting." Use this link for my news letter article on the use of portable gas generators in motion picture production.


- Guy Holt, Gaffer, ScreenLight & Grip, Lighting & Grip Rental in Boston
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Old 10-15-2010, 06:28 PM   #30
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Guy - what is Your relation to Eileen Ryan? You guys seam to be posting the same things and are both gaffers in Boston...

Peter
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