Archived posting to the Leica Users Group, 2000/05/20

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Subject: Re: [Leica] Cold light, dichroic
From: Mark Rabiner <>
Date: Sat, 20 May 2000 18:57:29 -0700
References: <>

Walter Levy wrote:
> Jeff Segawa asked how does a cold light head differ from a dichroic diffused
> head.  I'll tell you... I don't know.  All I know is I have to put these
> acetate multicontrast filters between the cold light head and the negative
> stage.  With dichroic head, you can just dial in your desired contrast...
> handy!

It's a graduated filter that passes in front of a blazing hot Hologon bulb.
As you turn the dial the filter is like a wheel which moves to a denser or less
dense part of its gradation
If you use the same "number" of gradation  (Say number 100) often that part will
fade and you will have "bumps' in your gradation.
ie 100 will be less filtration than 99 or even 98!

The Aristo VC 4500 head though works differently. 
It has two bulbs, both cool on the negs (so as to not pop them) florescents.
But one bulb is blue for the high contrast, (same as magenta)
And the other is Green for the low contrast, (same as yellow)
These bulbs don't have filters passing in front of them they ARE that color all
the time but work on dimmers.
So it's not a hot bulb with a dense filter in front of it.
Its a bulb that is just not turned up so high and would have been cool running
even if it were turned up high.
A much more efficient arrangement if you ask me!
Mark Rabiner

Replies: Reply from "Dan Post" <> (Re: [Leica] Cold light, dichroic (longwinded reply and editorial!))
In reply to: Message from "Walter Levy" <> ([Leica] Cold light, dichroic)