[pure-silver] Re: ZONE VI VC HEAD, was No More Below the Lens Polymax Filter Kits?

  • From: "mail1" <mail1@xxxxxxxxxxxxxxxxx>
  • To: <pure-silver@xxxxxxxxxxxxx>
  • Date: Sat, 7 Feb 2009 22:16:30 -0800

Rob, yes it is usable. In regards to the hump when I run a test using a step
table I prefer to match the step table densities to corresponding densities
in a negative. This means the step densities .05 to 1.40 when printed would
match the densities of a print made from a negative of the same density
range.  This test was overexposed because I used the same F stop, and Time
as the test without the cc40y filter. When I rerun the test I will change
the exposure time and this might smooth out the hump. If there is not a
calibration problem with the step table or the densitometer; which will have
to be checked; a hump sometimes indicates the different variable contrast
emulsions are not matching. The hump is in the toe area and therefore
effects the transition from mid range to highlights. 

I might find some time next week to rerun the test with a cc20y filter with
an adjusted exposure. Unfortunately it takes some effort to determine the
best combination of settings to keep the exposure compensation at a minimum
when a change in paper grade is made. I suspect the light sensor in the head
might not be in the best place for the clock to compensate for the increase
in light from the changing brightness of the tubes. I try to balance the
light intensities of the tubes so that the exposure stays the same as I
change paper grade. 

Cold cathode mercury tube variable contrast heads work on the principle of
adding blue light to the green light to increase the contrast. Usually the
green light output does not vary, an example of this is the Aristo vcl4500.
Some VCL4500 units have a rheostat to adjust the green light level to reach
the higher contrasts. The Zone VI also includes variable green and blue
light. The problem is how to decrease the green light as the blue light is
increased so that the light intensity stays the same so that the exposure
does not have to be adjusted with each contrast adjustment. This problem is
corrected better with incandescent light with filters. Dichotic filters
usually require some adjustment to exposure time. Some of the Durst Dichroic
heads have the ability to introduce neutral density to adjust for this
problem.

To avoid these complications I use a condenser enlarger by choice and cold
light when a negative calls out Cold Light. I also try to optimize my
negatives so they match paper grades that have curves that enhance each
other harmoniously. 

Jonathan Ayers  [mail1@xxxxxxxxxxxxxxxxx] 

-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Robert Krawiec
Sent: Saturday, February 07, 2009 12:31 PM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: ZONE VI VC HEAD, was No More Below the Lens
Polymax Filter Kits?

So it is usable with the filter? Does the abrupt hump you describe cause a
lot of issues?

Rob


--- On Sat, 2/7/09, mail1 <mail1@xxxxxxxxxxxxxxxxx> wrote:

> From: mail1 <mail1@xxxxxxxxxxxxxxxxx>
> Subject: [pure-silver] Re: ZONE VI VC HEAD, was No More Below the Lens
Polymax Filter Kits?
> To: pure-silver@xxxxxxxxxxxxx
> Date: Saturday, February 7, 2009, 1:03 PM
> Bob, greetings,
>  
> Rob had mentioned “Yes, this is more or less what I am
> seeing. It isn't the
> way the head is supposed to work though! I was told that
> placing a yellow
> filter (cc40y?) between the head and the neg stage will
> give you performance
> as expected, i.e. soft and hard at max should be close to
> grade 2, but I
> haven't tried it yet.”
>  
> I ran the test to verify what he was told, and yes the
> maximum soft and hard
> setting did in fact produce a grade 2. With out the filter
> addition these
> settings produced ES.78 effective grade 4 shot toe.
>  
>  Coincidently when looking for a cc40y filter I found a
> cc30y filter I had
> removed in the Zone VI Non VC cold light head.
>  
> The plotted curves from this test were distorted in the toe
> with quite an
> abrupt hump. The results without the filter were much
> smoother. I would
> normally rerun this test changing the exposure time for the
> added filter. I
> did not do this because I was studying the differences
> between having a
> filter and not.
>  
> Jonathan Ayers  [mail1@xxxxxxxxxxxxxxxxx]
>  
>  
>    _____  


      
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