CMY Filter Kit Enigma (academic question)

[AgX]

I got together with a monochrome Agfa Varioscop 66 MF-enlarger some loose parts.

Among these are CMY filters, one pair of filters per colour. They are true glass filters of 0.8mm (about half the thickness of taking filter panes). Each filter is mounted in a chromed steel frame. Each pair consists of one filter to be mounted in the variable filtration part and a 2nd filter of same density to be added to highten the filtration by 100units. Each pair was designated and packed as spare. Well finished. The panes have even ground edges.

My first question was. "Why would someone, seemingly at same time, order all three filter pairs"

The early samples (early 50s) of the respective Agfa colour head still had gelatin filters (likely laminated between glass panes). So I assume when they faded the true glass filters were available meanwhile and were bought (the packaging looks 70s).
However the colour head manual from 1961 explicitely states the filters being from massive glass and colourfast, but nevertheless in detail hints at changing the filters, gives the order numbers, even got an addendum with new order numbers. As if those glass filters are consumables...


Each filter mount carries a figure with one decimal. Crudely written by hand onto the mount. By etching-ink resp. by pulsed welder. Each pair has a different mean value.
What does that refer too and why was such needed ??


The static mounts all have at one side the designation "Upper Side" althoug both sides are identical.
Why such designation?

 

[Bill Burk]

It was probably Ctein’s

 

[AgX]

I doubt he can write in German... as that is what the designation actually is in.

 

[ic-racer]

Are they dichroic filters. That is 'mirror filters?' Because, if they not, they will be dependent absorption of light by dye and irrespective if the dye is in the glass or sandwiched between the glass, there can be fading. Dichroic filters reflect the unwanted color away, and are therefore less susceptible to molecular damage from the photons messing with the electron energy levels of the conjugated dye molecules in standard absorption filters.

 

[AgX]

They are neither dichroitic nor dyed-gelatin filters, but of mineral coloured homogenous glas. Such filters do not fade.

 

[ic-racer]

They are neither dichroitic nor dyed-gelatin filters, but of mineral coloured homogenous glas. Such filters do not fade.

I don't know much about those in enlarger use. Maybe the first I have heard about it in an enlarger in this thread, have you ever seen these filters in an enlarger? Maybe the extra filters supplied due to breakage risk since they are so thin.

I'm curious can you post some pictures?

In the USA, one of the common color enlargers (Chromega) used acetate filters before switching to dichroic filters.

 

[AgX]

In spite of explicetly having been offered as spares they seem that rare that there is not even a trace on the net.

They are about 33x33mm and each mounted by flat springs in a surronding rectangular sheet steel frame that next to the filter leaves a opening of same size to act as window for an underlying filter to be partially pulled in front of that window. The static +100 filters are of same mount but got each a rod to go through the head casing to be pulled from their idle into their active position directly. The moveable filters of course are operated by gear over scaled turning knobs.

The most likely way to break the filter panes is by frontal impact as during handling loose. I guess they might survive even falling on hard ground. Once installed in the enlarger head they likely should be indestructable so to say.

Basically these filters are mechanically operated as the more recent dichroic glass panes. The major difference being their lesser Dmax, by this needing each a companion to be pulled-in to achieve densities above 100units.

 

[Bill Burk]

They sound cool. I bet the “wear” they might get so that you would have to replace them would be careless cleaning giving them scratches.

Or maybe they really are susceptible to fading in active use (to the extent that they fall out of calibration).