1/4, 1/3, 1/2 stops etc & determining CTB

R

rc444

Well-known member
We did an exercise at film school where we set the lights for a practice scene.

The final light reading we agreed upon (to set) was t5.6 1/3.

The tutor then described a way of translating than to the actual T stops on the camera. However, he was talking in fractions and things like this, and it was so mathematical that it went over my head and I just stopped listening at that point because it was so complicated.

I understand the basic principle of setting exposure, but do how do you set it if your meter gives a reading in fractions? t5.6 1/3 may be all well and good for the meter, but t5.6 1/3 doesn't actually exist on the camera, so how do they work that one out???

Also, I had a question about CTB. CTB seems to also be available in 1/4, 1/3 and 1/2 types. Under what shooting conditions would you use a different CTB? For instance, if you're shooting outside and the light changes, would you switch from a regular CTB to a 1/2 CTB gel?

Thanks,
rc
 
Hopefully someone here can help out on your t-stop question... I'll tackle the CTB one.

The jump from CTB to 1/2 CTB is 1300k, pretty big. I think if you were trying to match a cloudless and a cloudy day you could maybe use it, but that's a pretty big shift.

I use 1/2 CTB when I want indoor and outdoor to work together but seem somewhat natural...e.g. an indoor scene with windows with real daylight. If you want to avoid a one-color studio "look", split the difference with your tungsten lights and bring them up to 4300k, balance the cam for 4300k, and your outdoors will seem a natural blue. The other plus of this is that you won't lose 2/3 of the light from your tungstens like you would if you gelled full CTB. Of course, if you can gel the windows 1/2 CTO instead, you can balance for 3200k and save even more watts.

I'd say I also use 1/2 CTB alot as a backlight or kicker when I'm balanced to 3200k. Also makes for good "moonlight" if your director isn't opposed to the look. Most of the time I use 1/2 CTB, I'm really just looking for "a light blue gel" and not thinking "I need to get halfway to daylight".
 
When youre shooting on film you use the 1/4 and 1/3 CTB/CTO/MAgenta/Green's incombination to shoot a grey card and have the color timer corret the footage to Effectivly "CC" in the lab. Now what yo ucan do for example is this. lets say youre shooting for a warm sunny day look on film. you shoot a grey card with a 1/4 CTB or 1/2 CTB and maybe a 1/8th magenta filter to push the green up a bit. Then yo ushoot your grey card and send it to the lab. all the footage for the day will come back from the lab warm and yellowish with a hint of green.

you can use it in lighting a scene for example in a controlled situation, and shoot lets say, a room thats supposed to have a reddish yellow light in it, like a old lightbulb, but theres supposed to be normal light coming in through a crack in a door. What you do is, you shoot with a normal 32k lamp in the room, and you put a 1/2 CTB on the light coming in through the door. Then in CC, correct the blue out of the door light and it will push the internal light ot a warm yellow. The reason you do it this way is that the HVX200/A1/Z1 will tolerate slightly bluish light better than slightly yellowish/red. you wind up with a cleaner end product.

Plus you can se 1/4 CTB's and CTO's as effect lighting to change he texture of lights from different sources.
 
Hey TimurCivan, if you're using video, you'd just WB on set, not wait to fix it in post, right? Or would you not WB if it was going to push your footage toward red? Is that because of the color compression, or NTSC's difficulty with red, or something else?
I have a bunch of pastel cards I use for roughly the same purpose, I just WB to the blue card to get a warm yellow look, etc. It's really convienient because it's still possible to match settings after the sun goes behind a cloud, or for a uniform indoor/outdoor look.

I thought for sure you'd answer his t-stop question!
 
As far as fractions on your lens stop goes, it means you needed to stop down an additional 1/3 of a stop from 5.6. On an HVX/DVX the iris is calibrated in 1/6-stop increments, so once you spin the dial to where it exactly reads f/5.6, you'd stop down so you see the brightness change by two "ticks" (each being 1/6 stop, so the cumulative effect being 1/3 stop). If you went to f/6.8 you went one tick too far; f/6.8 = 1/2 stop more than 5.6 (and 1/2 stop = 3/6, you wanted to go 2/6 or 1/3).
 
Barry_Green said:
As far as fractions on your lens stop goes, it means you needed to stop down an additional 1/3 of a stop from 5.6. On an HVX/DVX the iris is calibrated in 1/6-stop increments, so once you spin the dial to where it exactly reads f/5.6, you'd stop down so you see the brightness change by two "ticks" (each being 1/6 stop, so the cumulative effect being 1/3 stop). If you went to f/6.8 you went one tick too far; f/6.8 = 1/2 stop more than 5.6 (and 1/2 stop = 3/6, you wanted to go 2/6 or 1/3).
Click to expand...
I probably confused people because I forgot to mention in my example that I was referring to film with regards to the t-stop question, not the HVX.
 
well, film or digital, doesnt really matter. When using Tstop, Fstop, digital or film, 1/2 a stop, a full stop or a quarter is the same thing relatively.

When we get readings in fractions, you basically just eyeball in between the two stops to see if you can get 4.0 and a 1/3rd, if its 1/2, then just keep in between the two stops.. Unless you are using professional cinema lenses that have increments of thirds...
 
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