Help lighting a chroma backdrop

[Mark Suszko]

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.

[Bill Davis]

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.

[Ian Maclean]

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.”

[Ian Maclean]

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.

[Dennis Size]

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

[Michael Palmer]

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.

https://www.truesun.com/philips_TL950.php
https://www.bulbs.com/eSpec.aspx?ID=9738&Ref=Base&RefId=21
https://www.advancetransformer.com/products/fluorescent-electronic.jsp?pbid=3

Good Luck
Michael Palmer

[Mark Suszko]

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.

[Ian Maclean]

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.

[Bill Davis]

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.

[Dennis Size]

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