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which first ASA rating or Toe/Knee adjustments


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#1 Mark Reynolds

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Posted 30 June 2007 - 08:43 PM

Hi all.

This is a 2 part question

1) I have been reading an article at

http://www.digitalci... HD Cameras ASA

on how to rate your camera. I have also read many other articles that differ from the above technique.
First of all i never use the camera straight out of the box, ,i always adjust my toe, knee and curves to get a few more stops out of the camera as well as dsc chart line up. (still Learning )

Should this be done before the camera is rated or after ?,
what are the consequences of either?.
also does anyone have any other techniques in rating cameras ?


2) how do you measure the latitude of your camera ?

Thanks Guys.
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#2 Michael Nash

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Posted 04 July 2007 - 05:58 PM

The purpose of "rating" a video camera is to be able to predict an approximate shooting f-stop for a given lighting setup. If you change your gamma or knee significantly, then you might also change your exposure to compensate for or take advantage of those adjustments. Looking at it that way, you'd want to rate your camera after you set up you "digital emulsion." It's a similar procedure to under-rating a film stock by one stop, with the intention of pull-processing the film.

But of course video cameras don't have a true or consistent exposure index, and you may still adjust your exposure depending on scene content and light levels anyway.

Latitude is defined as the amount you can over- or under-expose an image and still recover a "normal" looking image in post. Dynamic Range is a more appropriate term for the range of brightness that the camera can capture. You test both of these by bracketing exposures of a grayscale and sample subjects (like a person's face) and noting which iterations can be recovered acceptably, and noting which iterations produced unwanted results (like where detail in midtone is lost, and what happens to skin color at various exposure). Overexposed video images often lose fine detail and color becomes pastel or artificial-looking; underexposed video images tend to accumulate noise.
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#3 Mark Reynolds

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Posted 06 July 2007 - 01:40 AM

The purpose of "rating" a video camera is to be able to predict an approximate shooting f-stop for a given lighting setup. If you change your gamma or knee significantly, then you might also change your exposure to compensate for or take advantage of those adjustments. Looking at it that way, you'd want to rate your camera after you set up you "digital emulsion." It's a similar procedure to under-rating a film stock by one stop, with the intention of pull-processing the film.

But of course video cameras don't have a true or consistent exposure index, and you may still adjust your exposure depending on scene content and light levels anyway.

Latitude is defined as the amount you can over- or under-expose an image and still recover a "normal" looking image in post. Dynamic Range is a more appropriate term for the range of brightness that the camera can capture. You test both of these by bracketing exposures of a grayscale and sample subjects (like a person's face) and noting which iterations can be recovered acceptably, and noting which iterations produced unwanted results (like where detail in midtone is lost, and what happens to skin color at various exposure). Overexposed video images often lose fine detail and color becomes pastel or artificial-looking; underexposed video images tend to accumulate noise.



Thanks you for the break down and clarification Michael
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Media Blackout - Custom Cables and AKS

Glidecam

Ritter Battery

rebotnix Technologies

Opal

Visual Products

Gamma Ray Digital Inc

Aerial Filmworks

Rig Wheels Passport

Tai Audio

FJS International, LLC

Metropolis Post

CineTape

Wooden Camera

Paralinx LLC

Technodolly

CineLab