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

I have not had an opportunity to use the Zone VI 4x5 model.

With my Zone VI type 1 head maximum green and maximum blue settings produces
an ES.78 effective grade 4 shot toe curve.  With the Maximum blue lamp on
and green off the head produces ES 0.60, eff. grade 5 short toe. So it
appears the tubes might be different in the 4x5 head.

A thought about the apparent dimness of cold light heads.

My type 1 cold light have a lamp power supply / controller box which
measures 12x11x6 inches inside this box are two large transformers with
Variac controllers. This unit appears brighter than my Aristo VCL4500. This
is because the difference in tubes between the two light sources. The Zone
VI has phosphor coated tube with a wider spectrum of light than the VCL4500
which uses phosphor coated colored glass tubes so the spectrum is narrower.
Since the eyes response to blue tube is very low the VCL4500 appears darker.

I checked one of my print logs and noticed an 11-14 enlargement of a 6x6
dense negative, requiring a paper ES 1.2 was printed on Ilford MC Paper with
my Zone VI set at Max Green - Min-1 Blue which equaled eff. Grade 1. The
time of exposure was 12 sec. at f5.6 using a 90m/m Schneider APO lens. The
same negative printed on my Durst condenser enlarger 300 watt bulb at 110
VAC using an Ilford 0 filter; eff. grade 0. The time of exposure was 20 sec.
f 5.6 105m/m Rodagon Apo lens. If we allow for the difference in lamp
heights because off lenses and the papers response to the different light
sources the exposures are similar. The image on the easel from the condenser
is quite bright compared to the Zone VI. The VCL4500 is dimmer still, and an
addition 1 stop grade 5 burn to the sky would have been difficult for me
because my eyes seem to have a poor response to the VCL 4500 blue lamp.

For large print on my Durst I use a 500 watt lamp run at 120 volts which
leaves the cold lights in the twilight zone.

I have noticed the different response photo paper has to each of the light
sources imparts a different rendition of the same negative. Cool.

Jonathan Ayers  [mail1@xxxxxxxxxxxxxxxxx] 
 

-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx
[mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Jean-David Beyer
Sent: Sunday, February 08, 2009 4:42 AM
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: ZONE VI VC HEAD, was No More Below the Lens
Polymax Filter Kits?

mail1 wrote (in part):
> 
> 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.

With my Zone VI VC head (a 4x5 model), I can adjust the green and blue tubes

separately.

> 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.

Since the Zone VI VC head is so dim, what I do is run either the green or 
the blue tube at maximum intensity so as to get as much light out of the 
unit as possible.

So for grades 00, 0, 1, and 2, I have the green at maximum.
For grades 2, 3, 4, and (wishful thinking) 5, I have the blue light at 
maximum. I calibrated things with a step tablet and a photometer so that 
Zone V always matches the grey card, using a constant 22 second exposure 
time. This results in apertures of f/8 for the extreme contrasts up to f/11 
for grade 2. Fortunately, my enlarging lenses can have their click-stops 
turned off. So part of my chart looks like this:

GRADE   SOFT    HARD    F/
00      MAX     OFF     8
0       MAX     B-      10
1       MAX     F       10
2       MAX     MAX     11
3       E       MAX     10
4       MIN     MAX     9
5       OFF     MAX     8

This is for Ilford MGIV VC paper in my version of D-72 developer 1+2 using a

Kodak T-14 step wedge in my enlarger's negative holder for an 11x14
enlargement.

> 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.
> 



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