Dichroic filters have a metallic coating that is deposited on the glass in a vacuum. There is little or no chance of them fading. However, lamps age, diffusion chambers can become something else then their original color, if it was around smokers that could create color changes over time, if your enlarger is not voltage stabilized then changes in line voltage can change the lamp's color output, etc., etc.Originally Posted by Jac@stafford.net
On some of the Durst colorheads, the filters can bind in the movement range... Set the controls to 0 cc and turn on the enlarger cold while just viewing the light while projecting onto a piece of white paper... Rotate the cc knobs for each color, and look for the color to darken as you turn each knob... Flip the filter in/out lever a few times and see if it goes back to the same color setting... Allow the head to get hot, and repeat above... See if there is a full movement of the filters when turned...
If not, how to fix??? Maybe not so easy... You can carefully clean the shafts and sliders with a solvent such as lighter fluid, and re-grease with silicone grease, and check the condition of the nylon gears inside near the lamp (and order a new set or two while you are at it), and push the shafts with your finger (while cold) and note resistance... If bad, you might just push the filters out of the way, and use MG filters as suggested above, or consider a new LED head...
My experience with the CLS heads that heavily used ones develop binding and sticking, and plastic parts inside can crumble, so plan on an upgrade if problems start... Get as many plastic spares as you can for the entire enlarger while you can if you intend to use a used enlarger long term...
Good Luck with it!!!
Steve K
Dichroics are not metal layers. They are related to AR coatings on modern lenses. Not that it matters. They do tend to be very stable with time. Any degradation would appear as flaking, dots, coating-itis. They cannot fade as the color you see is created by interference. That said, filtering LEDs with dichroics is problematic. Depends on the relative spectrums of the LEDs and the filters. Dichroics are so efficient at their filter bands and LED light color is specific to doping (unless the LED is 'white', then the color is regenerated by the phosphor in a more broadband fashion). If the light color and the filters don't line up properly, you will have non-linear behavior from your paper, as far as contrast is concerned. My suggestion, if you want to use the dichroic filter, use the lamp designed for the filters (which is a broad spectrum black-body radiator. If you want to use LEDs, use royal blue and bright green, as these will register the best with the spectral sensitivity of the paper. Then use split printing or variable contrast filters.
Best of luck. EW
I have to agree with Bob on this, the mixing chambers of some boxes can cause a loss, but I have been printing with Dichroic filters and never experienced a problem.
When using filters for Black and White that is a complete other monster and I am always buying new sets due to handling, heat and scratches.
Eric, most, if not all, lens coatings are metallic. One of the major benefits of the first coatings were that they made the glass much harder to scratch, since they were metallic.
Bob, not metallic. They have metals in them, sometimes, but what doesn't. Even hydrogen is a metal under some conditions. Metallic implies silvery, malleable, electrically conductive. Coating are things like magnesium fluoride, silicon dioxide, and many other oxides, sulfides, or fluorides. Depends on the base material, but one likes a high and a low index of refraction material to build layered filters. Metallic filters would tend to be neutral density type and not dichroic.
Dichroic filters made from glass do fade over time. I used to manage 1 hour labs and bulbs burning 10 hours a day will fade dichros over say 5 years. Now, you have an enlarger not on constant burn so they will or should last much longer
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But with the filters, they should be evenly colored if good, and not chipped/cracked/broken/blotchy and there... Then you are good to go... I have wrenched on many color heads and only rarely have the dichro filters been bad... So rarely the issue...
And the big one is if the unit is only being used for B/W, you have to come up with your own scale for the different grades... Now, if you were doing color printing, that would be a whole different matter...
Also, the lack of high contrast might be just that some papers don't have a ultra wide MG contrast range (like a paper might only be from grade 1 1/2 to maybe a little over 3 is not uncommon)... Try printing for higher contrast through only a very dark blue filter and see what you get... The paper's contrast layer is blue sensitive, so this will give that layer the max exposure... (Note/ the exposure will be very short...)
Steve K
I have an ancient Omega color head for my F. I found a plethora of problems inside the well used head after I purchased it, all of which would impact MG printing: the dichroic filters were very dirty, they were misaligned, the internal mechanisms to adjust them were jamming (so the dials read numbers the actual filters never got to) and the mixing chamber had changed color. I strongly strongly suggest you get inside that head and check the integrity of its operation you may be pleasantly surprised that a few hours of cleaning and adjusting will get things back on track.
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