Interview in front of window – ND gel questions

[John Sharaf]

Sophia,

To start off, there’s no need “to avoid this when possible”.

It’s the Cinematographers job to apply what ever solutions and techniques are required to best tell the story, and often staging a scene (or interview) while also looking out the window can be very important.
Think of a Wall Street tycoon in his big office in a skyscraper looking down on the rest of us!

So whatever the situation or script calls for, you should do your best to oblige. That doesn’t mean that it’ll be easy or cheap!

To your specific questions:

1 – does the gel need to cover the whole window or only the part that is visible behind the subject? In other words, you only see a small section of the window in the shot but is it enough to cover only that bit? For cost saving purposes, that would be great of course.

It’s best to cover the whole window; otherwise a lot of “extra” light is let into your shooting space and may be difficult to control. Furthermore the schedule may change and the sun or light might move into a problematic place that could ruin your earlier setup. Also despite your understanding that “you only see a small section of the window”, you must allow for the director to change his/her mind and want to get a wider shot too.

2 – is it actually practical to apply the gel in new, unknown locations? You don’t want to break anything obviously and don’t want it to slip down the window half way through the shot. Is gaffa tape the best solution or what works best for securing the gel to all sorts and types of windows?

When planning to gel a window, either a tech scout or at least a good set of photos of the location (taken at the time you’ll be shooting) is critical. This will help you determine how much gel and perhaps how much density you’ll need. You always want to put the gel on the outside, as it’s like a mirror and reflections become an issue; especially if it’s not smoothly applied and/or ripply. Also the best application is with sprayed slightly soapy water, the gel cut to fit and then smoothed with a squeegee. This method lends itself to quick and clean removal too after the job. If it’s a French Window, you’ll have to cut individual pieces for each frame of glass, and even if it’s a picture window you’ll have to make straight edge cuts so there’s no leak at the edges.

This gel also comes in Plexiglass 4×8′ pieces, which is very easy to apply, but of course very expensive.

3 – is 0.6 enough assuming that the light coming through the window isn’t overly bright, for example on an overcast day or if the sunlight exposure isn’t direct?

This is the $64000 question, and one which has both a technical and creative answer. The simplest way to determine the required density is to set the shot, light it with your biggest daylight source, set the exposure on the face, and then with that exposure in mind, continue to stop down until you’re satisfied with the outside exposure. If the difference is two stops (say T2.8 inside and T5.6 outside) then you’ll want to use .6ND. You’ll likely find that the difference (unless you have a 4K HMI in the room) will be more in the neighborhood of 4-8 stops, which requires a much denser gel. A lot depends on whether the picture outside is front lit, back lit and the weather clear, cloudy or overcast. A truly professional approach is to prepare for any or all possibilities. when you rent a grip truck package they have all the densities and you just pay for the one roll that you use.

Also be aware that the gel comes as both just ND and also Combination Daylight Correction and ND, refereed to as 85ND.x. This allows you to use Tungsten lights inside, but because they’re inherently inefficient and hot, this is rarely done. A variation on this would be to use uncorrected ND on the window and a 1/2 Blue (daylight Correction) on the Tungsten Light, on which you make your white balance.

Finally, may cameras these days have Log settings and or Cine Gamma (sometimes known as HyperGamma) that preserve more Dynamic Range in the picture, to as much as 14 stops, so that if the outside is 7 stops brighter than the face exposure, you’ll still have some detail, but you should still consider to lower that inside/outside ratio to taste, which is as I have said a creative decision.

You are now fully armed with the information you need.

Good luck!

JS

[Rick Wise]

John pretty well nails it. One more small detail: you don’t want to balance light intensities completely. The outside should be around 2-3 stops hotter than the inside. If they match, the scene looks fake. (It helps to have a spot meter to determine how hot the outside is vs. your f/stop inside.

Rosco makes a 2-stop scrim (https://www.rosco.com/filters/cinegel.cfm?CategoryID=4 — scroll down) that is not reflective. However it works best when it is not in focus, so it’s not so good if someone is standing/sitting close to the window. Another trick is to fly a super clean and seamless 8×8 double far enough back of the subject that it is not in sharp focus, but that cuts only one f/stop.

There’s a long thread on this forum about this topic which includes a Home Depot solution by Todd Terry: https://forums.creativecow.net/thread/47/856454

Rick Wise
Cinematographer
MFA/BFA Lighting and Camera Instructor Academy of Art University
San Francisco Bay Area
https://www.RickWiseDP.com

[Mark Suszko]

We use the combination color correction plus ND gel on our window shoots. It looks weird to the eye, kind of a dusky orange. We tended to apply it with scotch tape on the top most seam, and wet squeegee the rest of the way. Most of our portable lighting is still tungsten, and gelling tungsten lights to match daylight color temperature is REALLY inefficient, basically cuts the effective range of the light in half. So I lobbied the bosses to get us a joker-bug HMI as a better indoor solution.

There’s another trick method for dealing with the window, basically locking down the camera or using a motion control rig, then shooting the scene twice: once, a plate shot “window pass” without the person in the frame, and the shot exposed for the outside view. The second pass is lit to favor the subject and interior, and you can either let the window blow out over-bright, or gel it with ND, or even just cover it with green construction paper on the glass. You then composite the two shots and you have ultimate control over both elements. It’s a lot of work, may require rotoscoping and/or chromakey. You’re trading effort and time in post versus time and expense on the location.