De Vere Dichromat head - fade?
Was recently told by a reputable dealer that the De Vere Dichromat heads should never need the filters changed as the colour is impregnated into the glass rather than a surface coating and are virtually unfadeable. I'm not convinved, especially on say an enlarger that has been used professionally on a daily basis. What's peoples experience on these heads and changing the filters.
Theory says they should not need changing... Dichroic filters consist of multiple thin-film deposits on a glass substrate (a bit like the coating on a lens) it is not a coloured dye. IIRC, they rely on interference to reflect unwanted wavelengths and allow wanted ones through. They should last indefinitely.
That's the theory at least, others may have practical experience that contradicts theory as I guess it depends on the quality of the coatings and substrate which would need to be of low expansion glass because of the heat cycling.
Thanks, Bob. There is a heat reflective glass before the Dichroic filters and seeing as this is a De Vere it is built well.
They do fade, especially the magenta. I can go run the old filter through a densitometer if you insist, but the fade is significant and easily visible. The filters on both my 504 and 810H were very faded. On both of those enlarger, the heat absorbing glass is on the mixing chamber. As such the filters are between the lamp and the heat absorbing glass, and so they get seriously nuked with heat.
Originally Posted by HolgaPhile
Filters can be obtained quite reasonably from Focal Point in Florida.
However said that they don't fade is demonstrably wrong.
the guys in canada who do devere stuff now told me they would'nt fade as well but i was dubious. i have a 10x10 devere vertical.
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I've got a horizontal one. I'd prefer a vertical one, but I don't have the space. At least now I can give kids rides, as the carriage is motorized.
I'd like to put the question to rest about dichroic filters fading. When my company Focal Point was in it's hay days we rebuilt literally hundreds of color heads each year. Believe me Dichroic filters fade. This having been said if you aren't a pro lab that uses the enlarger every day at least 8 hours per day, it will take a decade or two to notice any difference in your enlargements.
Singe bulb heads aren't so much of a problem but with multiple bulbs and multiple sets of filters the fade will become noticable since your color enlargements will have a shift in color from side to side. Devere's, as all multiple bulb enlargers, will show the color shift in mostly in broad expanses of the same color. Like a grey backdrop.
If you begin seeing color shift in your photos don't start replacing filters though. There are other causes that could be causing the problem. All of you with multiple bulb heads should take the bulbs out and put them on a light table sometime. Unless you religiously replace all the bulbs in the head when one blows you'll see somr pretty amazing color differences in the light that's passed through the bulb reflectors. I've known many pro labs that would buy a full case of bulbs and inspect them on a light table and match colors before putting any replacement bulbs in the heads. Bulbs from a single manufacturer can vary slightly but you'll see dramtic color differences from one manufacturer to another. I suggest that you never mix bulb manufacterers in multiple bulb heads. It's a formula for crappy enlargements.
You also may need to replace the lamp sockets if you see color shifts. Older sockets will not pass current as efficiently as new ones and if all bulbs don't get the same voltage on them they'll burn at different colors.
I suggest that you make a standard negative of an evenly lit sheet of background paper. Then try and print an 18% grey photo to test evenness of the color in your head. If you can't get perfectly even color over the entire print begin with the bulbs, then lamps sockets, then replace the mixing chamber lining, test printing after each change. If you can't get the color shift out by then you have faded filters. Magenta filters fade the fastest, then cyan, then yellow. Since a full set of filters for a four bulb head is several hundred dollars I suggest changing the magentas first. That usually takes care of your color shift problems. If not then the cyan set is next. It's seldom that you have to replace the yellow filters but it's not unheard of either. When we rebuilt a head everything was changed out. Sockets, bulbs, all filters, and mixing chamber liner.
If anyone has any questions let me know. I no longer sell filters or rebuild heads though. The business in replacement parts, and head rebuilds just isn't there any longer. I can't afford to purchase nor stock the filters in large enough quantities (100 of each color) to be able to charge a reasonable amount to make me money and not require customers to take a second mortgage on thier homes to pay me.
Such is life.
I'm happy to have found this site though. Darkroom photography is still an art form and it's nice to see some people wanting to keep it alive.
Mike, thanks for the response, my head is a single bulb unit and I am in the process of changing the holder and bulb itself. I have also been told the single bulb units are better for home use as you have a longer exposure time and are not worried about pumping images out by the hour. Bulb wise they seem to be used in disco lighting a lot so you can get them for £6. But, I have been told you need a special one for the De Vere and guess what, it's £14. The filters are tempting but my £100 eBay enlarger will double if not triple in what I originally payed out.
This enlarger has been used on an industrial, basis and I know the filters have been changed, not sure how faded they actually are though unless I replace them.