t-stops and f-stops

[Bryce W.]

If you were to light a match in a black room, what would be the minimum t and f stop required to get a good picture?

 

[Zeb B]

get a good picture?

of what?

 

[David Mullen ASC]

Yes, of what? A face lit by that match? How far away would the match be from the face? The room itself? But it's black, isn't it? So even a big light isn't going to do much to make it less than black.

Exposure is controlled by sensitivity, lens aperture, and exposure time, so asking what f-stop is needed without providing the other factors is an impossible question to answer.

And what defines a "good picture"?

 

[Alexander Ibrahim]

I assume that you wish to take a picture of something illuminated by the match.

I also assume that you are asking to get a practical example to further your understanding of the difference between f-stops and t-stops.

Assuming that you are using a fixed sensor at an equivalent of 2500 ISO, with the match approximately 1 foot from the subject, throwing roughly one footcandle, the answer is:

You need a t-stop of 1.4

but the F-stop required will vary by which lens you are using. They will, on average, require f/1.3

There are a lot assumptions there ... the most uncontrollable being the amount of light put out by a single match. Different kinds of matches will put out wide variations of light level ... but even in a single box of matches different matches will vary in light output.

 

[Bryce W.]

The face lit by the match when held in front of the face about a foot away.
A good picture would be not over or underexposed.

What I'm asking more particularly now is if a zoom lens has a t-stop of 3.5, would it be possible in any way to get a properly exposed picture of a person holding a match to his face about a foot away. If so, can anyone tell me how I would do this?

 

[Stephen Williams]

The face lit by the match when held in front of the face about a foot away.
A good picture would be not over or underexposed.

What I'm asking more particularly now is if a zoom lens has a t-stop of 3.5, would it be possible in any way to get a properly exposed picture of a person holding a match to his face about a foot away. If so, can anyone tell me how I would do this?

Bring the match closer to the face, 5 inches will do thw trick.

 

[Matt Uhry]

If you've got no options give it a try at T3.5 - Most DP's would look for a lens that was at least a T2 or faster for this kind of shot, and then probably still cheat some light on the background when the match was lit.

An interesting and very well cheated dark scene is Greg Toland's work in the beginning of the "Grapes of Wrath" where Henry Fonda walks around a dark house with a lantern. These guys were working with 2.8 lenses and ( making a guess - David Mullen will correct me in a second ) 50 asa filmstock...

Matt Uhry
www.mattuhry.com

 

[Zeb B]

At the recent Reducation Sir Ted demonstrated the use of the "video" style exposure metering on the 5" monitor and suggested that even the flame core should not be blown out. So expose for the flame core and bring the subject face close enough to the source to expose properly (60-70 IRE) or fake some fill light was my take away. This has nothing to do with T-stops but it the way I work for quick results.

 

[Alexander Ibrahim]

The face lit by the match when held in front of the face about a foot away.
A good picture would be not over or underexposed.

What I'm asking more particularly now is if a zoom lens has a t-stop of 3.5, would it be possible in any way to get a properly exposed picture of a person holding a match to his face about a foot away. If so, can anyone tell me how I would do this?

Well, that's relatively easy ... fill the room with some soft warm lights as ambient light. When the match is struck it will add to the existing ambient, adding up to a decent exposure.

In post, you use a power window on the subject for whom the match is the key light, and darken the rest.

No matter how you cut it though, you'll be exposing under key. I try to get the subject into the mid-tones of the image, but "proper" technical exposure would place a caucasian face about a stop over key. (So if you are metering a 4, your faces should reflect a 5.6 - not that this ever happens.)

I'd recommend using a prime for the shot that is f/2 or faster, and crank the ISO as high as you can accept, but at least 1600 with Red MX or Epic. (I used 1600 for one scene like this with a Canon 7D!) You'll get much better, more authentic feeling, results the closer your match is to being the true primary light source ... ideally with no fill at all.

 

[Bryce W.]

Is the MX good at keeping noise to a minimum in such a shot?

 

[Alexander Ibrahim]

Is the MX good at keeping noise to a minimum in such a shot?

Yes, its kind of fantastic. Epic is even better though.

What is your finished product?

While the MX can deliver a good 4K picture using such techniques, it will deliver fantastic 2K and 1080p deliverables that look as clean as if you shot under full lighting.

I still recommend renting a fast lens for that shot that is t/2 or faster.

Hell, for giggles I'd love to see the shot with a Noktor or the like, at t/1. I'd also hate to be the 1AC on that.

 

[Bryce W.]

I haven't shot anything yet. I am trying to get a sense of what lens I will need to do such shots. If you shoot in 2K though will that be good enough to put onto a theatre screen?

 

[Curtis Stanton]

Have you seen this thread http://173.199.159.58/forum/showthread.php?52584-Leo-and-REDlogFilm...&highlight=?

or

http://reduser.net/forum/showthread.php?39998-M-X-at-ISO-2000...

 

[Alexander Ibrahim]

I haven't shot anything yet. I am trying to get a sense of what lens I will need to do such shots. If you shoot in 2K though will that be good enough to put onto a theatre screen?

The vast majority of films are delivered at 2K resolution for theatrical display.

Also ... I second having a look at the Leo images.

I still suggest you get a faster lens.