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How To Overexpose A Stock


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#1 Patrick Ryan

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Posted 09 July 2007 - 08:31 PM

I have three questions about over-exposing a stock,

I understand that it allows for a denser negative and it can also act as a backup so you don't go crazy with underexposure.

My first question is how do you underexpose the stock? I see that 2/3's of a stop of ASA 500 is 320, but how do you caculate 2/3 of a stop? I'm pretty bad with math so if someone could explain the caculation I'd be very greatful.

Second when you shoot the grey card, if you have an ASA of 500 now its 320 (for the slight over-exposure) you shoot it at an ASA of 320 so it will be printend down, not 500. Correct?

My last, is will over exposueing a stop, already 2/3 of a stop over make your image to hot?

Thanks
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#2 Xavier Plaza

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Posted 09 July 2007 - 11:11 PM

My last, is will over exposueing a stop, already 2/3 of a stop over make your image to hot?


No, when you're talking about exposure (over/under), that's only about exposure, you can't make an image more warm or cool with exposure, perhaps just only obtain more rich or pure colors with different techniques but not make it hot...
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#3 Patrick Cooper

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Posted 12 July 2007 - 01:01 AM

"My first question is how do you underexpose the stock?"

Don't you mean overexpose? Rating a 500asa film as 320 would be overexposing.

"I see that 2/3's of a stop of ASA 500 is 320, but how do you caculate 2/3 of a stop? I'm pretty bad with math so if someone could explain the caculation I'd be very greatful."

Well one possible way you could do this is to take a light reading with your meter set at 500asa, take a mental note of whatever f stop is recommended and then look at the corresponding f stop engraving on the aperture ring on your lens and note the distance between it and the next smallest f stop value (larger aperture) next to it. Line up the initial f stop on the aperture ring opposite the aperture mark, or dot, and then rotate the aperture ring two thirds of the way towards the next f stop (the next largest aperture setting.)

Of course if your light meter has a 320asa setting, just use that and then set whatever f stop it recommends on your aperture ring.
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#4 Dominic Case

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Posted 12 July 2007 - 02:14 AM

My last, is will over exposueing a stop, already 2/3 of a stop over make your image to hot?

you can't make an image more warm or cool with exposure,

There's a language problem here.

Most people use the terms warm and cool to indicate colour casts - warm is a yellowy orange cast, cool is a bluish cast - these are the shifts you get if you are balanced for the wrong colour temperature. (Though a higher colour temperature is bluish, which we call cooler!)

But the term hot is often taken to mean overexposed: bright images, faded colours, blown highlights. It tends to give a very hot desert-like feel to an image. No colour shift involved.

Cold doesn't mean under-exposed though. Probably it means the same as cool, but more so: quite seriously blue.

It's never ever a good idea to use these terms if there is any danger of being misunderstood. Which is probably most of the time :(
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