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Rating Film ISO


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#1 Dominik Muench

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Posted 10 August 2005 - 07:26 PM

hi guys,


i was wondering, what is the point of rating film at different isos and what si the procedure to do so ?
lets say for example i have vision 2 500t and i want to rate it with an iso of 320, i set my lightmeter to 320 and expose for that iso ? and then ? i tell the lab they should handle it as 320 stock ? what difference does that make later on for the look of the film ?
thanks for the help.
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#2 Filip Plesha

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Posted 10 August 2005 - 07:40 PM

The point of rating film differently is to get it overexposed or underexposed.
In that case you don't tell the lab anything, it gets processed normally.

You could also rate it differently in case you intentionally want to get the look of pushed and pulled film, in which case you tell them to push or pull.

Another reason I can think of is that you dissagree with the EI on the box.
For example, you find that the film is actually a bit faster, or slower than Fuji and Kodak sells them as. In that case, you make your own EI test, and rate it as such.
Rating can sometimes be as subjective as printing.
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#3 Dominik Muench

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Posted 10 August 2005 - 08:06 PM

ah ok, that clears things up :)
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#4 Dominic Case

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Posted 10 August 2005 - 09:35 PM

lets say for example i have vision 2 500t and i want to rate it with an iso of 320, i set my lightmeter to 320 and expose for that iso ? and then ? i tell the lab they should handle it as 320 stock ?

In your example, if you rate at 320, and say nothing to the lab, they will process it as normal. Then you will get a negative that is 2/3 stop denser than it would be if you rated it according to the manufacturer's recommendation. You may want that because you think it works better, or because you want to be sure of minimisiing grain in a blow-up etc (as Filip says).

If you rate at 320 and then tell the lab to treat the film as 320EI, then they will pull-process 2/3 stop (underdeveloping), and the film will behave more as though that was its true rating. In other words, close to the density it would be if everything was normal.

Simply rating the film at a different speed (with normal process) is exactly the same as rating it normally and over or underexposing. Except that you can set the aperture straight off the meter reading, instead of having to remember to adjust up or down 2/3 stop or whatever.
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#5 John Pytlak RIP

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Posted 10 August 2005 - 10:13 PM

If you rate at 320 and then tell the lab to treat the film as 320EI, then they will pull-process 2/3 stop (underdeveloping), and the film will behave more as though that was its true rating.  In other words, close to the density it would be if everything was normal.


<{POST_SNAPBACK}>


Although it is certainly possible to offer push processing in 1/3 stop increments, I thought the logistics of offering so many choices have led most labs to offer only a push-1 and maybe a push-2 ECN-2 process.
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#6 Dominik Muench

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Posted 11 August 2005 - 01:59 AM

thanks for that, so a denser negative would result in finer grain and more saturated colors ?
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#7 Dominic Case

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Posted 11 August 2005 - 02:47 AM

I thought the logistics of offering so many choices have led most labs to offer only a push-1 and maybe a push-2 ECN-2 process

Good reality check, John. I was writing hypothetically, sticking to the figures in the example.

In reality, if asked to push (or pull) 2/3 of a stop, I think I'd call the DP and suggest that if the exposure is that close, then a standard process would be the best way to go.

so a denser negative would result in finer grain and more saturated colors ?

Did I say that?

I usually answer that a thinner neg will result in more graininess and less saturated colours (which is not quite the same thing). In general, you can get a slight increase in colour and reduction in graininess with increased exposure, but the effect soon levels out.
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#8 Dominik Muench

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Posted 11 August 2005 - 03:10 AM

Good reality check, John.  I was writing hypothetically, sticking to the figures in the example.

In reality, if asked to push (or pull) 2/3 of a stop, I think I'd call the DP and suggest that if the exposure is that close, then a standard process would be the best way to go.

Did I say that?

I usually answer that a thinner neg will result in more graininess and less saturated colours (which is not quite the same thing). In general, you can get a slight increase in colour and reduction in graininess with increased exposure, but the effect soon levels out.

<{POST_SNAPBACK}>



no i didnt want to say that, i just asked if thats the case :)

thanks for the help, i might just leave the iso rating as it is and get the propper filmstock for the proper scene :)
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#9 Filip Plesha

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Posted 11 August 2005 - 05:58 AM

One more thing. I don't know if this applies to motion picture stock too, but I'll mention it:

pull processing reduces contrast, somewhat reduces grain, and has a bit of a color shift: highlights tend to go a bit blue/cyan, and shadows go in the oposite direction (yellow-ish)

Push processing increases contrast, increases grain, highlights shift more to yellow, and shadows shift more to blue-ish.
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