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Help lighting a chroma backdrop

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Ian MacLean
Help lighting a chroma backdrop
on Jun 1, 2009 at 1:07:04 pm

I haven't much experience with this, and have a few specific backdrop lighting questions. My small studio has a 9' foot roll of green chroma paper, and I'll be shooting mostly medium shots of a single subject with a Panasonic HVX170 locked down, and tilted on its side. I am on a budget, but would like to do this as well as possible.

I plan on lighting the backdrop with two Impact VA903 Fluorescent Cool Lights,
http://www.bhphotovideo.com/c/product/537466-REG/Impact_VA903_2KI_VA903_Flu...

and I plan on supersaturating the screen by taping a LEE Filter (either #244 "Plus Green," or #243 "Fluorescent 3600K") over the reflector. Then controlling spill with black foil. Some quick questions:

-I assume that leaving some gaps in the attachment of the filter to the reflector would be good for heat dissipation. I shouldn't try to seal in the bulbs, in other words. I know the fluorescents aren't terribly hot, but there will be five of them in the dish.

-Each light puts out 7500 Lumens through 5 bulbs per light, though I can control and reduce the number of bulbs in use by switches on the back of the light. I'm hoping the two lights will be enough to light the backdrop, but have been advised I may need three.

-Not sure exactly what height to place the lights. Slightly above, or below the height of the subject?

-The lights have an included diffuser

and I'm not sure whether I should use it along with the green gel, just the gel, or not use the diffuser but, in addition to the green gel, use a sheet of diffuser gel. If so, specific info about recommended diffuser gel welcome. Of course I will play around and see what looks best, but any advice welcome. Many thanks for the help so far.



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Mark Suszko
Re: Help lighting a chroma backdrop
on Jun 1, 2009 at 3:55:50 pm

Since nobody else volunteered first, I'll throw in my 2 cents.

Super-saturating the screen using filter gel lights seems like overkill. The particular shade of green doesn't even matter all that much, though too much yellow gets you closer to skin tones and that's bad, but Beyond a certain amount, saturation is no longer the issue; flat, even level across the screen is, and as long as you have a strong contrast, you don't need it to glow like green neon to key well.

Do add diffusion, it can't hurt. Do add some venting for heat, even though the tubes don't get as hot as tungsten, traeating them gently will extend their life.

Use your zebra bars in the camera viewfinder, crank the iris up and down and note where the distribution of the zebras grows and dwindles. If it pools in certain hotspots, adjust the lighting until the screen uniformely trips the zebras when you crank the iris up and down, and you will be in the ballpartk.

Everybody has different criteria, but if I have a scope handy, In my initial setup like to see the green or blue screen at around 70-80 IRE, the idea being that your actual subject will still peak higher than the backdrop. For my particular setups, this is a good starting point where the green isn't overwhelming and causing edge fringes, but is still keying cleanly.


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Bill Davis
Re: Help lighting a chroma backdrop
on Jun 2, 2009 at 5:36:14 am

Yep. You're spending too much time THINKING about green screen and too little time actually doing it.

You likely won't need the extra green light filters. The green background color should be plenty. Mark is right, the color will be fine, you're task is lighting it evenly.

That's NOT going to be easy with scoop shaped insturments. Their parabolic shape will gather all the light and create hot spots. Think about it this way. If the greenscreen was a MIRROR would you be seeing a large even source of light, or bright spots of light? The wider you can spread the actual light sources, the more even your key. This is why using longer light emitting tubes such as long fluorescents are way better than any small array of lamps which is what you have with that fixture. Yes, you can do it with these, but plan on doing quite a bit of masking and garbage matting in your NLE because you WILL have hot spots with this type of lighting.

Also remember to keep as much separation as possible between the screen and the performers so that spill from the screen is kept off them.

Good luck. And let us know how things come out.



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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 2, 2009 at 6:56:04 pm

Many thanks for the advice. As something tells me there will others looking for info on setting up greenscreen on a budget, I'm going to share some of the information I've come across.

I only ordered my lights yesterday, have no direct experience with greenscreen, and am trying to squeeze every penny by making smart choices.

I think that, like many, I've ended up with Fluorescents to light the backdrop and tungsten halogens for my key and backlights (blew most of my budget on Lowel Rifa 88 [w 40 degree egg crate] softbox for key, reflectors for fill, Lowel Prolite for backlight, both with a good range of lamps / bulbs and dimmers [for mild dimming if needed]). The fluorescents are 5500k. I like the idea of inexpensive ($8 / 21"x24") green gels both for supersaturating the screen and for filtering out the daylight color in my small studio. The greener the light hitting the green paper backdrop, the less I'll have to use (and these lights give the option of how many of the 5 bulbs to use at any time), the more options in intensity range I'll have lighting the talent. I think this reasoning is sound, but do let me know if not.

I've had conflicting advice about fluorescent bulbs and how much (or any) diffusion they need if they are getting bounced off a backdrop. I think I'll just need to experiment, but maybe if I had it to do over again I'd buy long tube fluorescents to light the backdrop, as Bill Davis recommends. Oh well. I can always rig some kind of soft diffusion / softbox if indeed these screw-in bulbs need it.

I guess the rule for those new to lighting, that really doesn't get said clearly or often enough, is that "The bigger the surface area of the key, the softer the results will be."


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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 2, 2009 at 7:11:51 pm

I think also perhaps I didn't emphasize enough that I'm locking my camera down sideways, and will essentially be shooting in 'Portrait' rather than 'landscape' mode. 9:16, in other words, and tuning the camera lens / distance to only need effective greenscreen a little wider than a medium shot of seated talent. I'm hoping that's a limited backdrop a little easier to light than a full wall.


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Dennis Size
Re: Help lighting a chroma backdrop
on Jun 3, 2009 at 3:27:38 am

It would have been far more useful for you to have filled us in on all the details of your project from the very beginning -- especially the information you shared in the last few emails -- instead of the piecemeal approach you took (...starting wih the odd email about covering your lights with green fabric).

DS



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cowcowcowcowcow
Michael Palmer
Re: Help lighting a chroma backdrop
on Jun 3, 2009 at 4:52:37 am

I'll be interested to see how you like these little compact flos and how good they really work. I love how B&H prints "dimmable with switches"

I wouldn't call this reflector a parabolic reflector, its more like an intensifier found as an accessory with some brands of HMI's, and its hardly reflective. I honestly think you won't get a nice even source from 5-60watt compact florescent bulbs.

I too like T-12 and T-8 tubes if I want a florescent light.

You may be better off with a few T-8 shop light fixtures from a good electrical supplier and find some Advance Mark-5 T-8 ballast (Dimmable) and some Philips TL950 or TL930 T-8 tubes to install into these cheap fixture. The 9 stands for 90 plus CRI and the 50 and 30 refer to 5000K and 3000K. I built my T-8 system more than 10 years ago and all of them are still working. I used Kino housings and made remote ballast cases and built my own head feeders using the Amp connectors just like Kino Flo. The reason I made them is I hated renting Kinos because at that time they weren't like they are today and didn't burn as color constant as the Philips/Advance system.

If you go the DIY route you should still try and contain the back grounnd light from ever spilling onto your subject.

http://www.truesun.com/philips_TL950.php
http://www.bulbs.com/eSpec.aspx?ID=9738&Ref=Base&RefId=21
http://www.advancetransformer.com/products/fluorescent-electronic.jsp?pbid=...


Good Luck
Michael Palmer


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Mark Suszko
Re: Help lighting a chroma backdrop
on Jun 3, 2009 at 1:51:17 pm

Ian, these sideways 'portrait-style' shoots for digital signage, which I assume this is for, intrigue me. I haven't done one yet. Perhaps you could start another thread to talk more about that, in the cinematography forum, maybe. I'll keep an eye out for it.


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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 3, 2009 at 11:14:22 pm

Michael, thanks very much for the info. I'm going to start a new thread and repost your entry.

Re: Portrait mode: Mark, I wanted the cleanest high def footage possible, but was worried about the width of my greenscreen, my 16:9 camera image ratio, and the small room making the camera, talent, and backdrop all closer to each other than ideal.

It was suggested to me that if I turned the camera on its side, my medium shot of seated talent would get a significant boost of pixels for keying (1280 vertical pixels), and eliminate the widescreen dead space. I'll be using a compositor and outputing to 720p, so the larger than necessary size of the subject footage will do nothing but help the composited image quality. It's a win-win. I'm not sure what digital signage you're referring to, but that was my motive, and it seems a worthy setup. I'll post results in Cinematography as soon as I've run some tests, thanks for the suggestion.


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cowcowcowcowcow
Bill Davis
Re: Help lighting a chroma backdrop
on Jun 4, 2009 at 7:33:56 am

Ian,

I still don't think you're quite understanding the essential elements of setting up a workable key.

If I had to put a single aspect at the top of the list of what makes a good key easy to pull, it would probably be the SHOT GEOMETRY.

Let me explain. You have three key surfaces to deal with. The key screen at the back. The subject in the middle. And the imaging CCD behind the camera lens.

What you're going to discover is that one HUGE factor in pulling a clean key is how the distance between these three planes interact. Let's say you have 10 feet of usable room between the CCD and the wall. You'd expect to put the talent and the 5 foot mark for some separation from the key and you'll be fine. But you won't. Not ONLY will you likely get spill from the green screen in 5 feet - but since if the talent is at 5 feet from the lens, about the ONLY shot you'll get without a super wide angle lens adaptor is a medium head and shoulders frame. And if you do that - your idea about turning the camera on it's side will result in you giving the talent almost NO arm room, so you'll typically constrict the talent's ability to gesture.

So you move the camera back to 15 feet. And get yourself 7.5 feet fore and aft the subject. But suddenly the geometry of the shot means that the key screen you thought was large enough at 10 x 10 shrinks down to the point where an arm gesture, once again, will fall OFF the key screen.

Suddenly you start to understand why full length green screens are typically VERY big - and are placed in VERY deep studios where there's often 30 or 40 feet of depth available.

That's what makes the geometry of a good green screen studio work well - and also why most of them don't have a few light fixtures illuminating them, but rather bank after bank of broad, soft color balanced sources.

The geometry of good key shots is relentless. Distance from camera to subject is critical to allow you to get as much of head to toe shot as you need. And further distance from the talent to the screen is important to avoid spill.

And trying to somehow overcome these lighting and shot geometry issues with ideas like gelling lights and turning cameras on their side are looking at solving issues that aren't the primary ones you really have to solve to pull a good key.

My advice is to FIRST set up your space and your shot as best you can. Learn the LIMITATIONS of your lens verses the geometry of your shot. Accept that all you may be able to do is get a head, or head and shoulders shot with the space you have. Then concentrate on lighting the actual SHOT - rather than wasting too much time on the tricky stuff like double gelling thisaway or turning the camera thataway.

My 2 cents anyway. Good luck and let us know how it turns out.



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Dennis Size
Re: Help lighting a chroma backdrop
on Jun 4, 2009 at 1:03:20 pm

BILL:
This is an excellent analysis , and superior advice. Unfortunately, I feel it won't be understood as most people, especially the inexperienced, fall into the trap of thinking the technology --- and using a few "tricks" -- is all that matters .... and, erroniously, what comes first.

DS




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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 4, 2009 at 7:03:16 pm

-"...You're spending too much time THINKING about green screen and too little time actually doing it."

Well, it's hard to 'do it' when you don't have any tools. I like THINKING about how I'm going to film something, and what tools I need before I actually purchase them. I call that RESEARCH.

-"It would have been far more useful for you to have filled us in on all the details of your project from the very beginning -- especially the information you shared in the last few emails -- instead of the piecemeal approach you took (...starting wih the odd email about covering your lights with green fabric)."

Did you bother reading the first three sentences of this posting? What word didn't you understand? Indeed, there have been complaints about postings that are too vague, or poorly researched, and a call for topics with specific questions. I have tried to be specific, gracious, and thankful for valuable information, especially when it corrects inaccurate facts.

I think it would be far more useful for you to have followed Creative Cow guidelines:
"...our primary task as the owners and management of Creative COW is providing an atmosphere conducive to generating: ...A safe environment for students and other inexperienced individuals to enter discussions, whether presenting questions or answers."

-"I still don't think you're quite understanding the essential elements of setting up a workable key."

You think wrong. I'm not stupid, just inexperienced. I understand everything you're saying. And understood it before I saw your post. I knew I'd be working in a limited environment, and it was a prime consideration in my purchase of a Panasonic HPX170 ("The lens has a new focal length range, 3.9 to 51mm. In practical terms, the HVX200A is wider than the HVX200, and the HPX170 is wider than both of them"). That's the 35mm equivalent of a 28mm lens, and in my second sentence I clearly said I was shooting "mostly medium shots of a single subject..." Short of that subject being LeBron James singing Jesus Christ Superstar, I'm hoping I'll be able to manage.

I also understand the how the software works, and how the color data is captured, and plan on recording HD SDI out of the HPX170 straight into pro res 422, (that's 4:2:2, progressive [yes, I'm aware it's only 8 bits embedded in a 10-bit word]). No compression. I am ALL about as workable a key as I can get, and with this added color data I feel I might have a little lattitude to lower the IRE a bit to reduce green spill. Naturally, I'll need to experiment a bit, but sometimes the technology, in it's recent advancements, can come first. Especially in comparison to even the best hardware of only a few years ago.

Sadly, your forum software won't allow for stickies, or even FAQ's unique to each specific forum. I am always thinking of saving the next guy some time, so I'm going to repost your otherwise excellent summary under this new topic title: "essential elements of setting up a workable key." There are a lot of inexperienced people who are going to be coming to Creative Cow, and this may make those comments easier to find.

-"Unfortunately, I feel it won't be understood"

Perhaps save your condescension for when it's justified and try to keep the tone of this forum a bit more friendly. While you're at it, maybe you could stick to the topic (literally) by answering the direct, simple, technical questions being posted to the Cow. I'm still waiting on these:

-Not sure exactly what height to place the [backdrop] lights. Slightly above, or below the height of the subject?

-The fluorescents are 5500k. I like the idea of inexpensive ($8 / 21"x24") green gels both for supersaturating the screen and for filtering out the daylight color in my small [tungsten-lit] studio. The greener the light hitting the green paper backdrop, the less I'll have to use (and these lights give the option of how many of the 5 bulbs to use at any time), the more options in intensity range I'll have lighting the talent. I think this reasoning is sound, but do let me know if not.


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Dennis Size
Re: Help lighting a chroma backdrop
on Jun 4, 2009 at 10:44:28 pm

"....maybe you could stick to the topic (literally) by answering the direct, simple, technical questions being posted to the Cow.
I'm still waiting on these:

-Not sure exactly what height to place the [backdrop] lights. Slightly above, or below the height of the subject?"

Above the subject.


"-The fluorescents are 5500k. I like the idea of inexpensive ($8 / 21"x24") green gels both for supersaturating the screen and for filtering out the daylight color in my small [tungsten-lit] studio. The greener the light hitting the green paper backdrop, the less I'll have to use (and these lights give the option of how many of the 5 bulbs to use at any time), the more options in intensity range I'll have lighting the talent. I think this reasoning is sound, but do let me know if not."

It is not.
In 30 years of lighting greenscreens I've never once added green (whether it be fabric or mylar color correction) to the instrumentation.


DS






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cowcowcowcowcow
Curt Pair
Re: Help lighting a chroma backdrop
on Jun 4, 2009 at 11:34:54 pm

Ian,

While I can't speak for EVERYONE who has responded to this post... I can speak on behalf of Bill Davis. I've known him for over 10 years! He is an amazing editor and has a VAST amount of experience! In fact, I believe Bill was the guy in the chair on several of my "first attempts" at pulling off a key... I've learned alot since those days, believe me! Although an accomplished shooter, I believe Bill's perspective is coming from the edit chair. He's spent COUNTLESS hours editing anything you can think of... He KNOWS what he's talking about in the post production world.

Even though some of your decisions may seem sound and logical, those with experience may have a different approach. That doesn't mean that one approach is better or worse, it just means that someone has PROVEN results with a certain method.

I agree, I WOULD NOT use green gel on the background lights! That is overkill to the point of possibly being a detriment... It could result in MORE kick back or spill from the background... if anything, I typically go a completely DIFFERENT route and light my background in the OPPOSITE color spectrum from my talent (tungsten/daylight, separate, but equal!) I learned that from someone I know who works at ILM... if it works for them, why not! They are the KINGS of special effects shots. You know what? IT DOES WORK!

I'll also tell you that I have several sound technicians in my metro area that work for me AND my competitors... they've watched my methodology and then told my competition, only to have dismal results! I'm actually cool with that! There are certain tools that actually make the difference between a successful key and a lousy key.

Bill is correct... I've never put it in the terms of "geometry" but none the less, I agree. Separation is EVERYTHING when it comes to "spill" on your backgrounds. Now... keep in mind, if you are just going to have head and shoulders shots, you CAN have the background "seem" too small in your shot, as long as the subject NEVER leaves the green area. You CAN use, as Bill indicated, a "garbage" matte to "fill in" the areas you don't have enough green, provided that your subject has no "entrance" into that non-existent green area (i.e. hands waving around outside of the green background). Also, if for what ever reason I do shoot all tungsten lights for example for my keying efforts, I will use GEL on the back-light of the subject, only! I will use a 1/4 - 1/2 magenta gel to COMBAT the green spill in smaller set ups. That's an OPPOSITE color than green and helps reduce the spill. Nothing aids the loss of spill more than "space" ("Z" space if you will) between the subject and the background. I typically WILL NOT SHOOT A KEY in an environment where I CAN NOT get at LEAST 10 feet of separation! It will not work, without a LOT of post work... sometimes including roto-scoping!

We are often hired to come in behind others as a "last ditch effort" to get a good clean key... I've written SEVERAL posts on my methods, and I'm sure you can find them if you take the time... I will reiterate one thing: get a waveform monitor to measure your lighting on the background! My same buddy at ILM shared this fact with me about 8-9 years ago... I can't thank him enough for that one! That is the true "secret" to pulling off a clean, successful chroma key, especially in HD! Because Zebra stripes occur when a certain, designated IRE level is present... there is no way to know what that level is without a WFM! You may have the stripes set at 75, but the light level is really 82... the stripes will still be there! So even if your ENTIRE viewfinder has stripes... it may not be evenly lit! If you measured your light levels with a WFM, you'll KNOW if it's even! If you don't own one, RENT one! It WILL be worth it!

Pulling off a good key is all about lighting... it's not so much WHAT KIND of lights you're using, but how they are used. I will agree, these lights look a lot like Westcott TD5 Spider Lites. I use those nearly every single day as my "key light / fill light" for interviews... HOWEVER, I don't think they are appropriate for lighting a chroma background. I'd suggest a florescent along the lines of a Kino Flo or equivalent, or a "fresnel" that you can spot and flood. Again, if you don't have them, and they are accessible, consider renting them! They aren't that expensive to rent.

Many try to cut corners when shooting on a tight budget... unfortunately this can present NIGHTMARES in post when trying to key... I know... I tried everything for years... it never worked well... now, when I use a WFM, light evenly, and have enough separation, I can typically key something in 5 clicks of a mouse or less in "Keylight" inside of After Effects, with phenomenal results!

Bottom line is this: TEST, TEST, TEST! Set up your gear and shoot something... go back and try to key it in post! It may or may not work. YOU WILL LEARN something if you do that! I promise. Hopefully, the next time, if you had less than expected results, you won't make the same mistakes... After enough shoots, you won't make any! Don't make them in front of your client! That's the worst!

One last thing... I'd recommend that you do some research on your NLE or post application to find out what LEVEL of IRE to light your background for keying... for example... I had a client recently who wanted me to key the background at 40 IRE! That's nearly 1/2 of what I normally would do! He was CERTAIN this was correct... He told me he used "Ultimatte" do pull the keys. I emailed the company, they sent me specs. They prefer a 1:1 ratio of lighting for the subject and background. "If anything light the background BRIGHTER than the subject... The closer you can get the background to 80-82 IRE, the better!" (keep in mind, this is for THEIR program!) I shot the footage the way the client wanted... it was HORRIBLE! It didn't work... At the end of the shoot... I took 5 minutes to rearrange the lighting, put a subject in front of the camera, and shot about 10 seconds with an IRE level set to 81. I took a picture with my cell phone of the WFM, showing the "recommended settings"... The client later told me "the last little interview worked... the rest didn't!" Since, I've contacted EVERY manufacturer of a "keying" product, to find out the specified requirements for the best key... they vary, but if I ask a client what they're using, it always works out.

Good luck. Let us know how it comes out!

Curt

Curt Pair
Picture This Productions
Sony ICE Team
F900/F800/F350/PDW700/EX1/EX3/D790/D600
Adobe Premiere Pro CS3 HD/Matrox
Phoenix, AZ


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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 6, 2009 at 6:37:29 am

Curt,

Thanks very much for the detailed information and encouragement. I know I'm going to find it useful, and I'm very sure others will as well.

I'm delighted to hear of your experiences lighting with 'opposite' color spectrum as that (potentially) removes something about which I was a bit worried. Anything that makes things easier is always welcome.

Having said that, I must also completely agree with your attitude pushing shooters into testing. If you can only have two of the three (fast, cheap, good), I've structured my entire production to be unpressured by time. A luxury as I have no clients, and am working on a project that is all my own. I have been all about the research, and I'm about to be all about the testing (I get my lights next week). I will try it all ways, I will test these cheap lights and screw-in bulbs, I will see what my new camera likes and dislikes.

Jeez, I just thought of the horrible image of a makeup artist with one of those little airbrushes for makeup hitting my talent with red powder in the areas of green spill. Guess that wouldn't work...

I will test, I will see what works, I will adapt, I will keep coming back to these boards as they are an invaluable resource, and I promise to share what I've learned. Many thanks, again, for the help.


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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 9, 2009 at 12:31:43 am

Hmm, turns out supersaturation works well enough for Kino Flo to sell coated bulbs. Not much different from a gel, it seems. Mr. Size has never used added green. Perhaps simply because he's never heard of it:

"For the best results the screen needs to be lit evenly and with the best possible color saturation. Evenness is easily achieved using Kino Flos because of the soft quality of the light and the wide beam spread. The best saturation of color is achieved by using blue-spike lamps on blue screens and green-spike lamps on green screens. It’s not as much about how much light is used to light a screen, but rather what produces the best saturation of reflected blue or green light."

http://kinoflo.com/FYI/FAQs.htm

"Each Kino Flo® Visual Effects lamp displays a narrow band of light energy in the color spectrum. The phosphor inside each lamp produces a desired color, measured in nanometers (nm) at the highest point in the energy level. The colors include two types of blue light, and two hues of green light. The 420nm blue and the 525nm green are often used in traveling matte photography on bluescreen and greenscreen stages. Kino Flo recommends safety-coated blue 420nm lamps for bluescreen and safetycoated 525nm lamps for greenscreen applications. The safety coating cuts the ultraviolet end of the color spectrum to produce a cleaner matte."

http://kinoflo.com/Kino%20Flo%20lamps/Visual%20Effects%20and%20Designer%20C...

Respected poster to the The Cinematography Mailing List Geoff Boyle also seems to use the technique (I don't have a direct quote, however): "Super-saturating the screen helps considerably, but only if your subject isn't standing directly on the screen. If they are, then you're stuck with white light. If not, super-green Kinos work great, as do tungsten lights with Lee Fern Green #122 (a Geoff Boyle trick, and it works spectacularly well)."

I'll keep looking for information and I'll test as soon as possible the gels I have over 5500k fluorescent screw-ins coming through a diffuser included with the kit.


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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 9, 2009 at 12:39:53 am

They also seem to be liking supersaturation over on a RED forum:

"Just did some extensive green and blue screen testing both under daylight and tungsten settings. (over 100 setups with all the variables !)

We found we got the best results lighting with supergreen kino tubes on digi green screens, with daylight balanced FG/

Even under and overexposed shots could be pulled on tungsten and regular (not supergreen kino's) but they weren't as nice.

Every little bit helps.

__________________
John Brawley
Cinematographer
Sydney Australia
http://www.johnbrawley.com"


I'm not familiar with Kino Flo. If they sell a specialty bulb, can you use it in a a non-Kino fixture? I wonder how new these bulbs are, and whether there are any (Chinese?) copies out there. Will do further research.


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Dennis Size
Re: Help lighting a chroma backdrop
on Jun 9, 2009 at 3:18:39 am

Wow.... what will they think of next ? !

Thank you for sharing this great information Ian ....especially the website for those newfangled Kino Flo lights. Who knew such fluorescent technology even existed?
I hope I have the opportunity to try them someday.

DS



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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 9, 2009 at 7:01:00 am

"The best saturation of color is achieved by using ...green-spike lamps on green screens. It’s not as much about how much light is used to light a screen, but rather what produces the best saturation of reflected blue or green light."


Your attempt at clueless sarcasm actually sounds closer to real truth on this topic. Just in case, as you're STILL not demonstrating a real grasp of the topic or the information I post, these are green producing Kino Flo fluorescent bulbs, specifically made for (what's this topic title again?) lighting chroma backdrops. Your hostile condemnation of supersaturating a chroma screen, in practice or even in theory, your careless / ignorant responses, and your heavy negative attitude somewhat discredit you from further comment, and as I started this topic I'll ask you to leave it to those interested in (and capable of) honest discussions of practical set lighting.

I'm sure expensive Kino Flow lights have a number of advantages, and from a preliminary scan of the website, it doesn't look like their bulbs would be compatible with other Fluoro fixtures.

Their use is interesting, especially in that "Each Kino Flo® Visual Effects lamp displays a narrow band of light energy in the color spectrum. The phosphor inside each lamp produces a desired color, measured in nanometers (nm) at the highest point in the energy level." So they're actually generating a green spike in a desirable frequency, and are probably much more efficient than a gel filtering out standard 5500k and only letting through what the daylight fluoro bulb produces in its green frequency. So that is a knock against trying it the inexpensive way. There is one other possible benefit of using the gel -cutting ultraviolet from the backdrop. I'd like to know more about that.

I'd also like a greater understanding of the relationship of that green bulbs' color measurement in nanometers to color temp in Kelvin.

"...safetycoated 525nm lamps for greenscreen applications. The safety coating cuts the ultraviolet end of the color spectrum to produce a cleaner matte."


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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 9, 2009 at 7:52:22 am

Damn, I don't know much about Planckian temperature, but these 525nm bad boys


http://www.filmtools.com/kino-flo-green-550nm-55w-compact-55c-k5x.html

look like some potent stuff:



http://upload.wikimedia.org/wikipedia/commons/b/ba/PlanckianLocus.png

Better than throwing a gel over a 5500 bulb. Now I really must know whether it's possible to build a fixture that will run them well, and what it would cost.

ps The info from the RED board may be colored (npi) by the fact that the camera's sensor is tuned to work optimally with daylight color. I found that interesting.


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Michael Palmer
Re: Help lighting a chroma backdrop
on Jun 9, 2009 at 3:29:44 pm

Ian,

Here are some quotes from some extremely talented people with extensive green screen experience.

Mark Suszko
"Super-saturating the screen using filter gel lights seems like overkill. The particular shade of green doesn't even matter all that much, though too much yellow gets you closer to skin tones and that's bad, but Beyond a certain amount, saturation is no longer the issue; flat, even level across the screen is, and as long as you have a strong contrast, you don't need it to glow like green neon to key well. "

Bill Davis,
"You're spending too much time THINKING about green screen and too little time actually doing it.

The geometry of good key shots is relentless. Distance from camera to subject is critical to allow you to get as much of head to toe shot as you need. And further distance from the talent to the screen is important to avoid spill. "


Ian if you only have a 14x12 room with 9' ceiling you may not want to use super green tubes as this is mainly used on very large studio stages for CGI block buster feature films where there is sufficient room to work with. The biggest problem you are facing is not having enough room to work. If you plan on adding green gel or using green tubes you will need to control these units so that none of the raw light hits your subject. If you don't have any lighting experience you most likely will over light the green and this mass amount of green bounce will fall onto your subject and you will have major issues in post pulling a key.

In a room this small my advice is to use the same color temperature units on the green screen and on your subject. My suggestion with the Philips T-8 tubes would be cost effective and you can get plenty of light from 2-4' 2 tube units for the green screen and you can select either 3000k or 5000k to match up with you Key (main subject) light. You may even want to use them as your Key and Back light and keep everything the same. You may also want to paint the ceiling and side walls Black and consult with a good Key Grip to help you order some grip gear so you can set some Floopy Siders and top Teezer to control the green screen bounce.

The best way to learn lighting is to turn every light OFF on the set and turn each unit on individually to see just where the light falls, this will train your eye to see where light needs to be added or eliminated.

Ian you have been given great advise here, and I couldn't agree more with Bill Davis's quote, ""You're spending too much time THINKING about green screen and too little time actually doing it. ".

Ian Please keep responses positive or I will moderate (delete) your post.

Good Luck
Michael Palmer


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Dennis Size
Re: Help lighting a chroma backdrop
on Jun 9, 2009 at 3:42:06 pm

IAN....Thank you so much for sharing your incredible wealth of knowledge on this topic.
Some of us just have no idea what we're doing, so your invaluable research will be quite a asset.
When one has no experience, and forced to work under tight budget constraints in a tiny studio, you have provided wonderful goals to target, and hopefully try to attain.

For those of us who can't afford real greenscreen fabric, and can only light our green paper with cheap Impact Fluros, you have shown us a "brass ring" to reach for. Perhaps someday some of us might get to actually use one of those neat Kino Flo lights you know so much about. I'm looking forward to more of your wonderfully informative posts. I find your graphs especially cool (I love all those pretty colors)!
While I'm waiting, I'll pass the time trying to figure out how high to place my meager Impact fixtures and how to use this complicated diffuser that came with it.
After a few weeks -- and with the assistance of your excellent advice -- I'll try to get the courage to attempt that neat trick you described about putting green gel on the fixture. Could you clarify one more thing, instead of using that plastic gel, is it possible to just use green hair gel or even green Jello?
DS





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Ian MacLean
Re: Help lighting a chroma backdrop
on Jun 9, 2009 at 4:42:19 pm

Michael

Thanks very much for the considered advice. If I'm unable to get my Impact kit to light evenly, I will certainly return them and go with your recommendation. It'll be more research and work, building a DIY fixture, but gratifying as well. I'm very grateful for your expounding on the capabilities of these newer bulbs as, like most uninformed or inexperienced people, I have a bias against 'old' fluorescent technology and the mood it created in film lighting.

I am going to keep doing research on supersaturation as there seem to be two possibilities: Either the physics is sound and one may be able to build a DIY replacement for Kino ParaZip fixture, then put in the specialty Kino bulbs, which come in small 21" size and are reasonably priced (around $30), or Kino just likes selling expensive bulbs for profit.

http://www.bhphotovideo.com/c/product/434715-REG/Kino_Flo_55C_K5X_Compact_L...

Your statement that my use of such bulbs would "most likely will over light the green" suggests that they are, in fact, a valid and even effective means of lighting a chroma backdrop, so I want to know more about the option to do so. It may well be that supersaturation is only a practical option for those who can afford several $1200 ParaZip fixtures. If so, that's good information for those doing the same research I have been.

And Curt, I forgot to mention that I am aware of the benefits of a waveform monitor, and had always considered having a laptop with the software that provided such. Sadly, I'm on the mac side, and those options are limited. It was a definite factor in my research for a camera, and I'm very happy that my HPX170 has a built-in WFM which I'll be able to see on a 24" monitor in my studio. So I do have that capacity to help me tune my lighting. Thanks again for the excellent advice.

I'm also delighted, Michael, that you have the capability to delete posts that are negative in tone. Please, if you can, carefully read these topics I've started, and see whether I am anything but humble and grateful when I get good help. If you can block Dennis Size from further posts that would be great as he's a definite negative influence on my topic here, which I feel has some interesting and valuable information. Many thanks.


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