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EXPOSURE and LIGHT METERS


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#1 Aaron_Farrugia

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Posted 10 April 2006 - 02:11 AM

hello ive just got a small question
ive been shooting digital for a long time and
aboutt to shoot film for the first time
16mm that is

and i had a question about the f and t stops

when i go ahead and get a reading, of just say f4 for example
does that mean that i go to the lens and set it to f4 or do i set it to T4??
thanks
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#2 Stephen Williams

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Posted 10 April 2006 - 02:16 AM

hello ive just got a small question
ive been shooting digital for a long time and
aboutt to shoot film for the first time
16mm that is

and i had a question about the f and t stops

when i go ahead and get a reading, of just say f4 for example
does that mean that i go to the lens and set it to f4 or do i set it to T4??
thanks


Hi,

If your lens is marked in T stops use them. T stops (Light Transmission) are corrected for any light lost through the glass so are more accurate than F stops that are mathematically calculated.

Stephen
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#3 Aaron_Farrugia

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Posted 10 April 2006 - 02:18 AM

yeah the lens im using has both t and f stops marked on it
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#4 Jamie Metzger

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Posted 10 April 2006 - 03:36 AM

Depends on your light meter; some can read in F and some can read in T or both.

Make sure you overexpose about 1/3 - 2/3 if you are using vision 2 (depending on which stock somewhat), but for your first time shooting film, it's better to have a ton of production lights with you ( I mean 2 arri kits would do), and a super bright image, rather than an underexposed one.
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#5 Stephen Williams

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Posted 10 April 2006 - 03:50 AM

Depends on your light meter; some can read in F and some can read in T or both.


Hi,

AFAIK all light meters read F stops. The T stop is a corrected F stop for the light transmitted to the film.

People use light meters in different ways. I usually think how much over key do I want the highlights to be, and how the final scene is to look when choosing a T stop.

Ther was a time when Douglas Slocombe would decide the T stop (Often 5.6) and then twist his meter until it read what he wanted. After a time he stopped using a meter at all.

Stephen
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#6 Andrew Koch

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Posted 10 April 2006 - 06:11 AM

Depends on your light meter; some can read in F and some can read in T or both.

Make sure you overexpose about 1/3 - 2/3 if you are using vision 2 (depending on which stock somewhat), but for your first time shooting film, it's better to have a ton of production lights with you ( I mean 2 arri kits would do), and a super bright image, rather than an underexposed one.


Why would you say it is better to have a ton of production lights. The number and amount of lights depend on many different things, 1st, what is the story? What are you lighting, a large set, a tight closeup? A dark moody scene? a bright scene? Too many lights in a scene will create multiple shadows and look unnatural. If you are using 7218 vision2 500T, you will most likely have enough exposure from a 300 watt bulb. Excessively bright images are not inherently better than underexposed images. If you are trying to get comfortable with exposing film, start by trying to achieve normal exposure (exposing for the key) for one shot. Then increase and decrease your exposure in half stop increments to see what each one looks like. You may find that for different situations, "normal" exposure may not always be appropriate.

As for the 1/3- 2/3 overexposure for vision 2, I think that is good advice, however, I feel that the explanation is unclear for someone who is starting out with film (I mean this as no disrespect to the poster)

Generally cinematographers tend to overexpose color negative (not such a good thing to do in B&W, because of blocked up highlights) by 1/3 to 2/3 to give extra information on the film. This is done by rating the film at a different ASA than the one given by Kodak or Fuji. For example, if you are shooting 7218, which has an ASA of 500 and you wanted to overexpose the film by 2/3 of a stop, you would change the ASA on your lightmeter to 320. Shoot your greyscale and everything else at this setting. When you take your readings, expose normally as if the ASA were 320. So if your meter says 2.8, shoot it at 2.8. By doing this, you will automatically be overexposing your negative by 2/3 of a stop. When you make a print, the lab, will print it down back to normal. If everything goes correctly, the image should appear "normal"

When you overexpose and print down, you get richer blacks, better shadow detail, and less grain. If you underexpose and print up to normal, you will get milky blacks, more grain, and less shadow detail. Overexposure and printing down does not apply to just Vision2. It applies to Color negative in general. It does not apply to reversal. Overexposure with reversal is deadly.
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#7 Chris Keth

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Posted 10 April 2006 - 04:47 PM

Hi,

AFAIK all light meters read F stops. The T stop is a corrected F stop for the light transmitted to the film.

People use light meters in different ways. I usually think how much over key do I want the highlights to be, and how the final scene is to look when choosing a T stop.

Ther was a time when Douglas Slocombe would decide the T stop (Often 5.6) and then twist his meter until it read what he wanted. After a time he stopped using a meter at all.

Stephen



Ditto. I've never seen a meter that gives you T-Stops, since a T-Stop is for a given lens and not a general calculation.

In short, use T-Stops for setting exposure, since they take light loss inside the lens into account. Use F-Stops for calculations for depth of field since they are mathematically derived from the diameter of the open iris.
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#8 Aaron_Farrugia

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Posted 10 April 2006 - 06:46 PM

well were not shooting a movie as such
were just doing some stock tests just to get used to it
we did a small test last week but we exposed using the f stops on the lens
do you know what the point of having both f stops and t stops marked up on the lens is?
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#9 Eric Dinger

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Posted 10 April 2006 - 08:19 PM

If I'm not mistaken, F stops are used to set hyperfocal distance.
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#10 Stephen Williams

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Posted 11 April 2006 - 01:50 AM

well were not shooting a movie as such
were just doing some stock tests just to get used to it
we did a small test last week but we exposed using the f stops on the lens
do you know what the point of having both f stops and t stops marked up on the lens is?


Hi,

Depth of field is calculated in relation to F stops.

Stephen
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#11 Chris Keth

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Posted 12 April 2006 - 06:29 AM

Hi,

Depth of field is calculated in relation to F stops.

Stephen



Bingo. Any calculation not involving a qualtity of light is done with f-stops rather than T-stops. This is because f-stops are directly related to the diameter (and area) of the iris opening at that f-stops. A t-stop would actually be open wider than the number would indicate and DoF would be off as well as hyperfocal distance set incorrectly.
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#12 Dimitrios Koukas

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Posted 12 April 2006 - 07:39 AM

Use t-stops on the lens for proper exposure and put the same number for the f/stop reading at your light meter.
f/stops are calculated mathematically and t-stops is the actual openning of the lens iris that factory compensates for light loss.
(As Stephen allready explained).
Dimitrios Koukas
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