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increase/decrease stops


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#1 Jon Bel

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Posted 09 October 2010 - 08:31 AM

I'm currently reading Kodak's reference guide for filmmakers. I'm looking over the chart for conversion filters and I will be using the 85 filter to do some tests. It says that the exposure increase in stops is 2/3. I know what it's saying but just wanted to be sure. Does increase means close down or open up on lens or does it simplify things to just change exposure index on meter?

My meter is set at 320EI currently. My shutter angle is 120deg (older camera). My filter will be amber 85.
My manual says shutter at 120 - decrease 2/3 stops. Taking all this into consideration, how should I expose this?

I need cinematographer knowledge.
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#2 Kyle Reid

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Posted 09 October 2010 - 11:10 AM

I'm currently reading Kodak's reference guide for filmmakers. I'm looking over the chart for conversion filters and I will be using the 85 filter to do some tests. It says that the exposure increase in stops is 2/3. I know what it's saying but just wanted to be sure. Does increase means close down or open up on lens or does it simplify things to just change exposure index on meter?

My meter is set at 320EI currently. My shutter angle is 120deg (older camera). My filter will be amber 85.
My manual says shutter at 120 - decrease 2/3 stops. Taking all this into consideration, how should I expose this?

I need cinematographer knowledge.


It means that in order to compensate for the light lost (absorbed) by the 85 filter, that you need to open up the aperture to allow more light in. The amount of compensation needed is 2/3s of a stop, so to correctly compensate, open the aperture 2/3s of a stop. You can account for this change by setting your meter to a lower effective film speed. Since you are set at 320 film speed now, you can set your meter from 320 down to 200 film speed. This way you can meter, and correctly compensate for your light loss.
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#3 Jon Bel

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Posted 09 October 2010 - 04:45 PM

Thanks Kyle, just wanted to confirm this.



It means that in order to compensate for the light lost (absorbed) by the 85 filter, that you need to open up the aperture to allow more light in. The amount of compensation needed is 2/3s of a stop, so to correctly compensate, open the aperture 2/3s of a stop. You can account for this change by setting your meter to a lower effective film speed. Since you are set at 320 film speed now, you can set your meter from 320 down to 200 film speed. This way you can meter, and correctly compensate for your light loss.


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#4 Bill DiPietra

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Posted 09 October 2010 - 06:22 PM

In my experience, the manufacturer's recommended filter factor is very often a rather conservative one. You will probably find that you will need a full stop to compensate for the filter. If this is just a test roll, I would shoot at some different exposures and keep a record of each shot. This way, when you get the film back from the lab, you can see what worked and what didn't.
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