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LED Enlarger Head
Lately I have been considering building an LED light source to replace the projector bulb in my beseler dicro enlarger. I only enlarge B&W so I am not worried about the filtering in the head and I have heard that blue light is better for B&W than white. Is this true or am I better off getting white LED's.
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Graded paper is sensitive to blue light only, VC paper is sensitive to blue and green. If you plan to use VC paper, then the white LEDs would be better, this way you can use filters to change grades. If you are going to use only graded paper, then get the blue LEDs, you will have shorter printing times.
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A slowly moving project of mine is to build an LED enlarger head, although what I am looking to do is a bit different than what you are describing.
The difference in color temperature between a bulb and an white LED is significant, not only in center temperature, but in the quality of the light. White LEDs are actually blue LEDs with a phosphor on top that absorbs blue and emits various colors of light. The overall emission is perceived as white.
Presuming you are using VC paper, your filtration will have to be recalibrated when switching to an LED source - the amounts of blue and green light in the two sources are really quite different.
The brightest LEDs normally available are at www.luxeon.com - the 5W versions are really quite intense!
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Have a look here for some ideas on LED enlargers: http://www.huws.org.uk/
Cheers, Bob.
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Or you could try a bank of blue and a bank of green and vary the intensity of each to (try to) control contrast.
Hmmm...
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Huw's page, which Bob referenced above, explains how to do just that.
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Addendum...
This link does not have the advert banner: http://www.textklick.demon.co.uk.
Also, I see that Maplin in the UK now stock some of the Lumileds, which is nice....]
Cheers, Bob.
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For those of us that spilt filter isn't that head serious over kill? Just need to power the LEDs. Turn them on/off. No need to vary them to achieve contrast grades.
On the more complicated front. Somebody was talking about a red/green/blue head for colour work.
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 Originally Posted by Nick Zentena
For those of us that spilt filter isn't that head serious over kill? Just need to power the LEDs. Turn them on/off. No need to vary them to achieve contrast grades.
On the more complicated front. Somebody was talking about a red/green/blue head for colour work.
Yup, for split-grade printing two on/off switches will do, but that's what you get when an engineer gives himself a project: he's going to stick a microprocessor in there somewhere... Main problem I see is the lack of a grade 5 with the LEDs - a pity, but I guess one can live with that for split-grade printing and it's pretty rare to need grade 5 in normal printing in any case.
Colour is a different problem as you can't adjust the colour an LED emits: they will only emit very close to one specific wavelength (which is a useful property for a safelight). Not sure how you would get over that problem for printing colour.
Bob.
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I glanced at the website with the LEDs and the blue didn't seem that blue. 470 wavelength. Would something lower work better?
I don't really understand additive colour printing. My understanding is you make three exposures. You vary the colour by varying the relative exposure of each colour. So more red means a longer red exposure.
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