Shooting against pure white back drop
Just wanted some tips really, I have a shoot that requires the talent to be filming in front of a pure white backdrop.
I use Lite panles Bi colour so was wondering wether to go Tungsten or Daylight? Is there a preference? I have more daylight lights so that would be my choice.
Shall I expose the white at 90IRE or 100IRE?
Color temp should make no difference as long as it is all the same. Since you have more daylight instruments to me it'd just make sense to crank your LItePanels over to the daylight side.
Well I said "as long as it is all the same"... which of course it not totally true. In a setup light that I'll sometimes use a backlight that is a bit on the warm side, maybe not cranked all the way to tungsten, but somewhat. In many case a somewhat warmer back/side/hair light gives a good look, I think. Conversely, I recently worked with one client who preferred that his backlights were a bit cooler, so it's just a matter of personal pref and the look that you want. But as long as your key fill and backdrop lights are all the same temp, you should be good to go.
And I probably wouldn't shoot much above 90, if that. Definitely not 100.
And for what it's worth (and this was discussed recently in another thread), I've had to shoot white backgrounds about a zillion times (especially back in the days when the white limbo "Apple look" was in vogue), and after a few dozen times I finally realized that it was infinitely easier to do them greenscreen and insert the white plate in post. It just made for a much much easier shoot, easier lighting, and easier post. But you may have reasons that you need to do it practically, and of course it can be done.
Fantastic Plastic Entertainment, Inc.
Terry's done this a million times, and so have I. That's why I'm a little surprised that he did not recommend 80ire for white. That's the standard I have know and used for years, and has often been confirmed to me when I work on or visit other of these types of big time shoots; it's always 80ire.
The old time reason is that when video receivers were over modulated (either by video or audio) they would clamp it down. In video this meant that the foreground scene was pushed down too and became darker.
Nowadays we have mostly (non-CRT) displays that are essentially "over bright" in the whites. For all intent and purpose when the image is white, the display becomes a light). Your 80ire video is going to look like 100 on the screeen.
Of course a future of HDR displays threatens our current calculation. These displays are only able to have an extended dynamic range by making the brights even brighter. We can only hope the designers and engineers involved consider this common construct of white limbo as they fiddle further with our well intentioned imagery.
Bottom line; set the white where it looks best on your intended delivery system.
Actually while I've done it a million times, I haven't done it a million times practically... as I said the vast majority of the time I've greenscreened.
And yes, as John said you have to pay attention to your intended delivery system. I believe the last time I did it practically I had goosed the levels up to a normally-too-high 90ish because I knew the video was to be embedded on an all-white web page (and was sure the web designer would be using pure white), so I didn't want the white to appear too gray in the side-by-side immediately-adjacent comparison.
But mostly we do broadcast television, where usually what appears to be pure white in actuality isn't anywhere near 100% white (and the same for black). A lot depends on the end usage.
Fantastic Plastic Entertainment, Inc.
As Todd said, color temp doesn't really matter for these purposes.
He's also right that this kind of thing could be easier to accomplish with a greenscreen. We'd also need to know how tight your shot(s) will be. I'm assuming you want to light it such that the white behind the talent is even and creates a "white limbo"?
If so, and greenscreen isn't your best option, the most foolproof way I do this is to use 2 4'x4-bank kino flos. Remove the egg crate, place them at opposite sides of the white background mounted vertically and cross-shot them across the white. The kinos are a large enough source that, properly placed, they can fill an 8x8 or 12x12 white background evenly and without issue for medium or slightly wider shots. I would also place a black sider on them so none of the raw light spills onto the talent, this can be a 4x floppy, or really any black lightproof material.
Unless you have a bunch of them, and place them carefully so they fill in every shadow, litepanels by themselves are not an ideal choice for this as they aren't a large or soft enough source to fill a background very evenly, unless your shot is a CU where only a small part of the background is necessary to light. A larger and softer source is the way to go and would be an inexpensive rental.
Bear in mind that having enough space to property place lights and the talent so as to minimize/eliminate any unwanted spill from your background and key lights is critical as well.