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Film Latitude


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#1 Chris Jordan

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Posted 25 June 2008 - 10:54 AM

Hello All,

I'm having some trouble understanding what the latitude of film is and how to figure it out. Since I am learning this stuff on my own there are some things I just don't know. I don't understand how to read the curve and am having trouble finding any information out. This is probablly a stupid question, but as the saying goes, better to look stupid for a few minutes and ask the question, than stay stupid forever by not asking. Any help would be great.
Thank you.
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#2 Paul Bruening

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Posted 25 June 2008 - 01:23 PM

Not at all Chris. Everyone starts from somewhere. If you get the idea of f-stops then you can figure latitude out. In its simplest concept it's about the range of light that a film (or sensor, though more correctly called dynamic range, as was pointed out on another thread) can capture. That range is often calculated in f-stops since those are an easy standard of measure. Now, it's not so simple in it's most complex considerations like resolving power at each density... but that isn't a big deal for you. Right now, just think of it as the 11 numbers on the volume knob on a Fender guitar amp. It's the film's equivalent range in light power sensitivity.
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#3 DJ Joofa

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Posted 25 June 2008 - 09:24 PM

Wrote the following on a different thread, but is applicable here also:

Dynamic range is the number of variations you can have in your signal from pitch black to max white. "Tonal range" is an important parameter and that is typically the range a cinematographer has in mind that the image should have. They may not want to use the full range of variation that is offered by a camera for a few reasons and one is mentioned below. Since, by definition, the full range (dynamic range) of a camera is typically more than the range one wants to have in an image, the left over space or room is called latitude -- it is only useful in the post production after acquiring an image to shift the tonal range up or down for a more pleasing image.

Please bear in mind that the normally the print film (the one that will somehow get to projection in a theater) has typically a smaller number of variations between black and white than the original camera negative. Another way to say the same thing is that the dynamic range of print film is less than camera negative. However, that is fine, because once a cinematographer has decided that which portion of the larger dynamic range offered by the camera negative to be printed to film (i.e., the tonal range), they should strive to keep that tonal range not exceed the capacity of the print film.

There are several reasons that the print film variation (or dynamic range) is less than the camera negative, and one important one is that in a theater / cinema there is always some flare present that tries to reduce the contrast of projected film, hence, in order to compensate for that fact the print film has higher contrast than the camera negative, and that also makes its available range of variation less than camera negative.
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