Need new dichoic filters for color head for VC paper printing
Anyone have a source for the dichroic filters in color heads? I have an Omega Super Chromega D II color head, which was in production for decades and in wide commercial use.
I need yellow and magenta only, because I only print black and white VC. I could use the bare filters or the OEM arm/filter assembly. I'm real happy with this 4 X 5 head, fitted into my 5X7 metal Elwood with some cutting of the top casting. I'd like to keep it running, but the yellow filter especially has some visible fading.
I see many sources for dichroic filter blanks, but what to specify? These are optical companies and I have no idea what specific yellow and magenta would work in an enlarger for VC. OTOH, any thin glass dichroic filter that could be cut to fit the little windows in the metal holder arm would work. A "stronger" filter than the one used in color heads like the Omega would actually be better, if it was available. Many workers are using gel filters for the extremes of contrast with VC papers since the original dichroic filters are not that strong in filtration and don't produce the maximum the paper is capable of.
I'd like to try a commercial dicroic filter if I knew which category to buy. Any ideas? For example, are the filters in color heads additive or subtractive? How is strength of the filter specified? What passband is best for yellow and magenta for VC? Answers here might help a lot of users in the future as enlargers get older and start to fail, with no replacement parts to be had.
Thanks, Todd Foster.
It's a long story, but I was recommended these filters for my DeVere 507: http://www.edmundoptics.com/onlineca...d=1734&showall
It's been a while since I delved into this arcane subject so I think they should be additive ones - the subtractive is also available from the link above. My project has stalled due to not having access to a dark enough room to use the dang thing!
“Do your work, then step back. The only path to serenity.” - Lao Tzu
These were available as replacement parts, so you should be able to order them from either KHB or Harry. I think the cost is around $30 per filter, but I'm not sure on that part.
There they are!
Originally Posted by ic-racer
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What about reversing the filter in the holder as a stop gap measure? The trailign edge has rarely ever been in the light path. That being siad, the further you dial in the filter, the less colour stauration if you are dialing in the most faded bit.
The other option if you usually use Y to some degree, ala printing RA-4 is to put a CP or CC above the negative, taped to the top of the neg holder for say 50cc's, and then use the faded to dial in the last 5-80 units needed. I do this when trying to wring high contrast from old VC papers - max magenta ala Ilford grade 5, and magenta from the dichroic head.
my real name, imagine that.
If you are going to throw away the faded filters, I'd like them. I'm trying to collect faded dichroic filters. (have yet to find one........)
More on those filters, and thanks for great info!
Thanks to all that contributed to answer my question, very helpful.
Mike's idea of reversing the filter so the faded edge is not the one entering the light beam is a good one, as well as using supplementary gel filtration above the neg. I have gels, I could do that.
I'm looking into the Edmund filters, which are $35 for a 50mm square. Harry says he measured the original at 20mm, so the Edmund filters should cut into 4 replacement sized filters. Harry suggests a diamond tip glass cutter which I don't have. This idea gets my interest, because combining Mike's idea of supplementary filtration with new dichroics makes me wonder if I couldn't put in a double layer of the new filter to kill 2 birds with one stone? If they're thin enough, they could both fit nearly within the thickness of the filter arm and see how that works.
I think I'll get just the yellow in case it's a complete bust, which I doubt. That's the one with a faded area near the leading edge. The magenta seems even enough, but looks like some pinholes have appeared. This head was heavily used in commercial color printing for many years. Lots of photon impacts on those "non fading" dichroic surfaces, not to mention heat. Since I'm doing this, I might as well get new filters in both once I see what happens with the yellow.
ic-racer: why do you want faded filters for a collection with no members yet?
I'm curious. I'll not throw them out when the time comes just in case.
Best, Todd Foster.
I was going to send it back to Omega and try to get a new filter in exchange. But I guess you could do that also
Originally Posted by Todd Foster
Here is another source, looks like 2" square is $12.80 USD
Last edited by ic-racer; 10-31-2010 at 09:06 PM. Click to view previous post history.
Please report back on how this all works out for you. I'll be looking at doing the same.