[pure-silver] Re: Under exposed frame
- From: "Rob Champagne" <app@xxxxxxxxxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Wed, 05 Jan 2005 15:12:32 +0000
At 04/01/2005 21:38 -0500, you wrote:
>From: XRadar@xxxxxxx
>Subject: [pure-silver] Re: Under exposed frame
>Date: Tue, 4 Jan 2005 19:07:05 EST
>
>> Are you saying that by using the 2 filters in separate exposures you
>> can produce a paper curve different then can be obtained using a
>> single filter setting for one exposure?
>
>Right.
>
>> I always thought that anything that two filters used separately
>> could produce could be duplicated with one filter assuming that
>> filter was perfect for the contrast needed.
>
>In split filter printing, this is usually the case.
>
>> Or are you taking advantage of some nonlinear paper response to
>> extreme filters?
>
>This is taking advantage of nonlinearity of individual silver halide
>crystals (threshold effect). In order to do this, the exposure with G5
>filter must be very brief so that only the deep shadows areas are
>developable when not combined with the main G2 exposure.
I don't follow this reasoning. According to Ilfords data sheets (which are not
always reliable), all of the blue sensitive emulsions are of the same speed and
they constitute the high contrast element of the print. The green emulsions
have varying speeds and they constitute the low contrast element of the print.
The blue emulsions being of the same speed are therefore cumulative across
different exposures and any threshold of that accumulation would be taken up by
the first exposure if it was the G2 exposure or the G5 exposure if it was the
first exposure. Ilfords charts show the blue emulsions characteristic curves
all originating from the same point.
discuss.
>--
>Ryuji Suzuki
>"Keep a good head and always carry a light camera."
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