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exposure with k40?


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#1 Michael Althaus

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Posted 09 June 2006 - 12:05 PM

I used my Arriflex 16S/B with built in lightmeter for the first time. I don't have a handheld lightmeter yet.
I used Kodakrome K40 and got a little confused when I set the lightmeter. I shot outdors so I had to use a 85B filter since K40 is tungsten balanced film. I set the lightmeter to ASA 25 but I'm not sure if it's right. The lightmeter mesures through the filter so why do I have to compensate 2/3 stop for the filter? Isn't there a difference if you use a handheld lightmeter or if you use the built in lightmeter?
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#2 John Pytlak RIP

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Posted 09 June 2006 - 02:26 PM

I used my Arriflex 16S/B with built in lightmeter for the first time. I don't have a handheld lightmeter yet.
I used Kodakrome K40 and got a little confused when I set the lightmeter. I shot outdors so I had to use a 85B filter since K40 is tungsten balanced film. I set the lightmeter to ASA 25 but I'm not sure if it's right. The lightmeter mesures through the filter so why do I have to compensate 2/3 stop for the filter? Isn't there a difference if you use a handheld lightmeter or if you use the built in lightmeter?


AFAIK, if the built-in meter is indeed measuring the light coming through the lens, you would use EI-40 as the film rating. Using a filter in front of the lens reduces the light for both the film and the meter, so the 2/3 stop "filter factor" for an 85B is already compensated.

Yes, for a handheld meter, you rate an EI-40 tungsten film as EI-25 daylight, as the 85B is only affecting the light reaching the film, so you need a "filter factor" for the meter.
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#3 Michael Althaus

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Posted 10 June 2006 - 07:40 AM

So I rate the film at ASA 40 if I shoot outdors with a builtin lightmeter (that messures through the lens) and if I use a handheld lightmeter, I rate it ASA 25 to compensate for the filter. That was the way a thought it was but I did it wrong. That means I overexposed everything by 2/3 stop. Should be still usable, right? The latitue of K40 is around 6-8 stops, right?
Thank you for your help...
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#4 Bryan Darling

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Posted 10 June 2006 - 03:27 PM

The latitude of K40 is around 6-8 stops, right?
Thank you for your help...

K40's latitude is no where near 6-8 stops. That's the latitude of modern color negative film stocks. You may have about 3 stops. What you need to understand is that latitude doesn't necessarily correlate to overexposing and everything coming out fine...especially with reversal film and especially with Kodachrome. Latitude is the range of stops a film will "see." For instance most modern negative stops will have about 8 stops depending. So let's say that the "correct" exposure for your subject and scene is f5.6. The film will capture (see) anything that is f4, f3.5, f2.8, f1.9. Additionally it will capture anything at f8, f16, f22, f32.

Now while it may have captured all that information, that doesn't mean that everything it captured will look the same. What I mean is that everything below the 5.6 will be darker and perceived as darker. Everything above the 5.6 will be brighter and perceived as brighter.

Ok, so let's say that Reversal has about 1 1/2 stops under and about 1 stop over. I am perhaps being conservative but better to be conservative that way out there. If your "correct" exposure for your subject and scene was 5.6 but you shot f8 (1 stop under) then the film would capture everything up to f5.6 and everything down to say f16. But that means that anything that was at 5.6, what should be "correct," is twice as dark as it should have been. This means your shadow/dark areas or what should have been your shadow/dark areas will be twice as dark. So when a lot of your scene is being put in the "dark" part of the film there isn't much left for the brighter areas. So now your brighter areas have become more gray.

I know this may seem rather overwhelming. I hope I've explained it to some degree why latitude won't make up for bad exposures per se. I will say that with wide exposure range, it does make it easier to correct for bad exposures later in the telecine or printing process. Since reversal is designed to be directly projected, it requires your exposures to be extremely accurate otherwise it will appear too dark or too bright. Everyone goes through this when their first starting out. You have to make mistakes in order to learn. We've all gone through it, it's part of the curriculum :)
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#5 John Pytlak RIP

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Posted 12 June 2006 - 03:34 PM

KODACHROME film is not very forgiving of overexposure. At 2/3 stop overexposed, expect to see washed out highlights and pasty flesh tones. Don't confuse exposure latitude with dynamic range (sensitometric straight line) of a film.
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