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Help with exposure and filter in regards to handheld lightmeter


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#1 Fabian Prell

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Posted 27 April 2009 - 12:11 PM

Hi there,

I am planning to shoot a short on Super 8. Just have two questions regarding the correct exposure:

1.My Nizo has a shutter angle of 150 Degrees (or 151 as the manual says).

I am going to shoot at 24fps, which gives this a shutterspeed of 1/57.

As I am using a vision2 200T, so the in-built lightmeter will not recognize the stock and I cant use it.

As a result I am using a handheld lightmeter. The Lightmeter I am using is fixed at 180Degrees.

So lets say I set everything correct in Lightmeter (24fps, 200T), and the Lightmeter gives me a reading of 4.0 stops.

What should I set my camera to (in regards to the difference between the 150Degrees on the cam and the 180Degrees the lightmeter is set to).

How do I calculate the difference? Is there a formula? Or do I just overexpose by 1/2 - 1 stop when shooting?

2 I am shooting outside. But I am using a 200t (tungsten). To correct this I am using the in-built correction filter of the nizo. How much light do I loose through it? Should I still keep the lightmeter set to 200T, even when shooting outside with the correction filter? If the lightmeter gives me 4.0 at 24fps and 200T, how do I set my camera to make up for the light-loss of the filter?

Many thanks!
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#2 Chris Millar

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Posted 27 April 2009 - 07:36 PM

180/151 = 1.19205298013245

Put this into an inverse Log2 calculator like here

and you'll get your answer ...

0.253448 i.e. a 1/4 of a stop which makes sense once you have a think about how shutter angles affect exposure, a 1 stop adjustment would account for a halving or doubling of the shutter angle (try out the numbers)

as it works in ratios you'll get the same answer for 151/180 (the reciprocal of 1.1920...) - again try it if you please ;)

You just need to interpret the +/- sign... in your case you need to open the iris to account for the metering/shutter angle difference
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#3 Jim Carlile

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Posted 27 April 2009 - 08:12 PM

The 200T will work fine with the Nizo 561's exposure meter. It will be set at ASA 100, which is deliberate on Kodak's part-- they advise a one-stop overexposure.

If you don't want this, just take a reading and then close down the aperture one stop.

I recommend using the auto meter over a handheld. If you use a hand meter, you must also compensate for the loss in the lens and light path, which is about 3/4 of a stop in that camera.

To make it easier, just set the hand meter to a 1/60th setting-- don't worry about shutter angles-- you've already taken this into consideration when you calculate the shutter speed.

The lighmeter "angle" is different than the shutter angle of the camera, BTW. Just set the meter at 1/60th.
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#4 Art Leal

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Posted 27 April 2009 - 09:50 PM

The 200T will work fine with the Nizo 561's exposure meter. It will be set at ASA 100, which is deliberate on Kodak's part-- they advise a one-stop overexposure.

If you don't want this, just take a reading and then close down the aperture one stop.

I recommend using the auto meter over a handheld. If you use a hand meter, you must also compensate for the loss in the lens and light path, which is about 3/4 of a stop in that camera.

To make it easier, just set the hand meter to a 1/60th setting-- don't worry about shutter angles-- you've already taken this into consideration when you calculate the shutter speed.

The lighmeter "angle" is different than the shutter angle of the camera, BTW. Just set the meter at 1/60th.


Jim:

Was wondering if setting the lightmeter to 1/60th is something you recommend for this specific model or a general rule when using them with S8 cameras. Thanks
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#5 Fabian Prell

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Posted 28 April 2009 - 02:24 PM

Thanks for all the answers, I just want to summarize this in my own words to see if I understand correctly, verication appreciated:

1. With 16mm and 35mm there is no lightloss from the lense to he film, correct? That is why the lightmeter gives you the stops, that you should set the lense to (Or at least the lightmeter is already set to account for the stoploss in 16mm and 35mm cams).
However, on a the Nizo 651, there is a specific lightloss, between the lense and the gate, which a handheld light meter does not take into account: 3/4 of a stop, correct?

2. The lightmeter of the Nizo rates 200T Kodak V2 as ASA100. Thats why I can use the in built camera reading and close down by one stop (If I wanted to expose on the spot). That would mean, that for every 100 ASA less that a filmstock has, I can simply compensate by opening up the aperture by one stop. That means if the light meter give me a 5.0 reading at 500ASA film, it will give me a 3.0 reading at 300ASA, a 2.0 reading at 200ASA and so on (just an example to understand how the ratio works)?

3. Now to the 1/60 shutterspeed setting on the hand-held lightmeter:
The shutterspeed of a Nizo with 24fps and a shutterangle of 151 Degrees is 1/57.
So you set the lightmeter to 1/60 because its the closest it can get to 1/57? This would mean that the shutterangle of 151 is basically set in the lightmeter by the 1/60 shutterspeed, correct?
It sounds correct to me, just by logic and maths, my question now is:

Does the 1/60 setting on the lightmeter take the 2/3 stop loss of the lightpath into account already or not? Or would I do a reading with the external lightmeter at 1/60 shutterspeed (24fps, ASA200 for 200T) and open up the aperture by 2/3 of a stop on top of it?

I will probably go with the lightmeter of the camera. Lets say I want to expose for the highlights, then I would have to walk to the area with the highlight and take a quite close reading with the camera to get the reading for the highlights, like a refelective lightmeter, just that i have to go close to the object, right? The lightmeter of the camera does not recognize the zooming in from a distance and close down its reading area, does it?

This hole thing just made me a bit worried of how to actually expose best for the highlights with the camera now... or how to control what I expose in the picture.. thats why I thought a handheld lightmeter would the best option... hmm.. seems like it isn't with the nizo's...

Sorry for the long post, just want to know how to control exactly what i will get as result. No room for experiments in his upcoming shortfilm of mine...and no time for tests anymore either..
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#6 Richard Tuohy

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Posted 28 April 2009 - 07:00 PM

I agree with Jim.
Use the internal light meter of the camera if you aren't in a position time wise to shoot a callibration test to callibrate a hand held meter to the camera.

You are quite correct that most 16 and 35mm cameras with reflex viewfinders have a mirrored shutter and thus there isn't light lost by the reflex system. Instead the viewfinder will 'blink' with each exposure as the mirrored shutter rotates. Bolex 16mm reflex cameras aren't like that however, and neither are super 8 cameras (except the beaulieu models). So there are as Jim said, two issues, one is the shutter opening, the other is the light loss of the reflex viewfinder system.

As for the 85 filter question, if you use the internal light meter then you don't have to take that in to account. if you used an external meter, you would certainly have to take the filter in to account as well. An 85 filter absorbs 2/3rds of a stop of light.

If you want to use the hand held meter and you don't have the will to do a test, then (and this applies to shooting negative film ONLY - if it was reversal film you MUST shoot a test as there is no latitude to the exposure) I would factor the following: 1/3rd of a stop for the shutter, 2/3rds for the reflex viewfinder, 2/3rds for the filter and another 1/3rd to either fatten the neg up, or to compensate for the inacuracy of the previous approximate compensations. That makes for 2 stops. I would then set the ASA on the light meter to 2 stops UNDER that of the rated speed of the film. Thus, for 200t I would set it to 50 asa. Since you have taken the shutter in to account, you can then use the meter as a CINE meter - and use its FPS settings (18, 24 etc)..

But I don't think you should do that. You should just use the NIZO meter as read and have a 1 stop over exposure (if that is indeed what a nizo will do... you would have to rely on other people for that one, but Jim seems to agree with you there). This would be catastrophic for reversal film, but quite o.k. for neg..

In your last post you showed some confusion about the way the asa series works. Remember it is a log series, not a linear series. Thus the difference between 100 asa and 200 asa is 1 stop, the difference between 200 and 400 is also 1 stop, and the difference between 100 and 400 is 2 stops (not 4 stops). 100 to 500 is 2 and 1/3rd stops. The familar numbers in the asa series are 1/3rd stops apart. Thus from 12 it is 12, 16, 20, 25, 32, 40, 50, 64, 80, 100, 125, 160, 200, 250, 320, 400, 500, 640, 800, 1000 etc..

hope that helps.
richard
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#7 Jim Carlile

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Posted 29 April 2009 - 02:00 AM

Those are all good questions, Fabian. I'll try to answer them.

All cameras and lenses suffer a pathway light loss. Most 35mm and 16mm camera lenses are measured in T-stops, which takes this fact into consideration, but super 8 cameras are not. Super 8 cameras also tend to have big zoom lenses and complicated internal light paths.

The "shutter speed" that you calculate does not take into consideration any light loss. It's only an approximation, too. Roughly put, 24 fps is about 1/55th in most non-XL cameras (like the 561) and 18 fps is about 1/40th, give or take.

So, you set the handheld meter to about 1/60th or so, then take a reading, and open up the lens to about 2/3 of a stop more, to compensate for the pathway light loss.

In negative film this isn't critical-- there's a lot of latitude to play around with, plus you can adjust most problems at the transfer stage. You don't even need to use an external 85 filter with this tungsten film, either, because the color cast can be removed in post.

The best thing to do is use the internal meter, and if you choose, close it down a little if you want it to resemble an ASA 200 setting. But it's not necessary with VISION films-- Kodak actually prefers it overexposed, which is why they deliberately set it up to read at ASA 100 in most cameras.

The difference between ASA 100 and 200 is one stop. But that's only because as the ASA doubles, you get a one-stop increase. So ASA 25 to ASA 50 is one stop, and ASA 25 to ASA 100 would be two stops-- it doubles at ASA 50, then doubles again at ASA 100. Going up the scale, ASA 500 would be one stop above ASA 250, and two stops above ASA 125, etc.

If you want to expose for the highlights, you're right-- either move in and zoom in, then 'fix' the reading at that point. Set it manually there if you have to. I'm not sure if that Nizo has a 'fix' button where you can lock the aperture at a desired setting. You may have to twirl the manual dial to set the aperture at a specific reading.

The easiest thing to do is use your Nizo meter as a reference-- it's actually a high quality Gossen, I believe, and just as good as any external handheld meter.
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#8 Fabian Prell

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Posted 29 April 2009 - 07:40 PM

Thanks for all the great answers! Great amount of knowledge!

To finalize the understanding of why film gets shot a certain way there are three more questions (before i feel confident to control super 8 to some extent;)):

Everyone recommends to overexpose by one stop when shooting with good colour negative film. Why is that?

To my understand it is for the following reasons:

1.Negative film shows increased grain when underexposed. Grain decreases (picture becomes rather grainless and fine) when slightly overexposed. So you basically prevent the film from becoming grainy, and you can then later in post, stop the footage down to the originaly intended exposure, without the grain it would have had.

2. Film looses details easier in the black areas, than in the bright areas. Therefore it is overexposed when shot and can be stopped down in the grading process, where the picture will then have the same amount of "brightness" as if it was correctly exposed, just that the detail in he black areas is preserved (and less grain), correct?

Would it make sense then to overexpose by one stop when shooting and then tell the filmlab to push it down one stop when developing? Would the result be an image, with the same "brightness" (or stop), as if it was exposed correctly on the shoot, just that there is more detail in the blacks, and less grain?

What would be the correct way to bring the image back to the correct exposure, once it has been shot intentionally overexposed.


3. Now a practical question for the upcoming short of mine (shooting this firday, first super8 shoot, wish me luck):

We are shooting a scene with a character inside a car. It will be daylight and there will be no extra lighting. My instinct from shooting with digital is the following:
If I expose the character correctly, the sky will burn out in the background and the information in the sky will be lost. Naturally I would then stop down so I can get some detail in the sky, without having the character too dark. In post i can then push it up slightly without burning out the sky.

Now negative film has a way bigger latitude in contrast and color-range when it comes shooting tricky light situations. But for this scene I am worried: If I (as everyone suggests with negative film) overexpose the character by one stop. The sky will loose detail completely, or not? Not only would I have lost information in the sky through the big contrast of light between the character and the sky, but also would I have overexposed by one stop, which would make me loose even more detail in the sky.
What I am asking is basically, will the 200t vision T accommodate to expose for the character in the car, overexpose by 1 stop and still see detail in the sky?
Or should I for this particular shot expose correctly, or even underexpose to get the blue sky in the background as well, AND the character (which is suppose to be the main focus of attention, so he has to come out decent)? What are the experiences there?

Many thanks!!
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#9 Jim Carlile

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Posted 30 April 2009 - 12:15 AM

Well, now you know why old time movie makers shot scenes in the a studio instead of outdoors.

The rule is, expose for the faces, for the characters, the actors, or whatever. If you try to get the exteriors in any kind of detail as well, you'll sink the faces-- they will be way underexposed.

This is just the kind of trade off you have to make-- the bright outdoors will get blown out by the correct interior exposure, but that's just the way it is. With negative film you'll have some detail-- enough-- but you have a choice to make: do you want to take pictures of the outside, or the inside?

You're basically correct about why a little overexposure is preferable for negative film. With overexposure you'll have more control over the transfer because you can do more with a thinner image than a dense one.

Right now, don't go pushing the film or anything-- just a bit of overexposure is enough. Whatever you do, have fun.

If you're near any kind of used bookstore, look for Independent Film Making, by Lenny Lipton. You can probably find a copy for about 99 cents. Read it through good-- it's a fun and easy book.
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