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#1
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help with light source for 8x10 enlarger
Hi,
I'm building a new light source for an Elwood 8x10 enlarger. Have modeled the diffusion box on the one in my Saunder 4x5 machine. However, the illumination is not yet even: about 1 stop drop-off from center to edge. I've researched Fresnel lenses, and believe one would work (12x12 lens with a FL of about 250 mm, I calculate). The source I've found is in China, and the price is not reasonable. Questions: Will the Fresnel lens actually increase the edge brightness? Is the FL about right for this enlarge size? Background: The light source is two assemblies from Ektagaphic projectors, 250 W each, beaming into the difussion box through side holes to create a large bright spot at the top of the box. Because of the size of this spot, I believe the FL of the Fresnel lens shouldn't be critical. Thanks |
#2
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help with light source for 8x10 enlarger
Rather than pointing to the top of the box, shouldn't the sources be
aimed to the side and top corners? |
#3
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help with light source for 8x10 enlarger
Bill,
I have had great succes (1/3 stop difference across the field) with an 10x12 diffusor, I use a scrap of white acrylic I had lying around, and 4 150W CFL bulbs, approx 4" above, spaced 5" apart, centered on each long side. I will be using an electric shutter for the exposure, so the start up time isn't an issue for me, though once warmed up, they are fairly consistent in brightness. The other option is to find a neon sign bender and have him make you a grid similar to the Aristo lights, shouldn't be very expensive at all. erie Bill wrote: Hi, I'm building a new light source for an Elwood 8x10 enlarger. Have modeled the diffusion box on the one in my Saunder 4x5 machine. However, the illumination is not yet even: about 1 stop drop-off from center to edge. I've researched Fresnel lenses, and believe one would work (12x12 lens with a FL of about 250 mm, I calculate). The source I've found is in China, and the price is not reasonable. Questions: Will the Fresnel lens actually increase the edge brightness? Is the FL about right for this enlarge size? Background: The light source is two assemblies from Ektagaphic projectors, 250 W each, beaming into the difussion box through side holes to create a large bright spot at the top of the box. Because of the size of this spot, I believe the FL of the Fresnel lens shouldn't be critical. Thanks |
#4
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help with light source for 8x10 enlarger
John J wrote:
Rather than pointing to the top of the box, shouldn't the sources be aimed to the side and top corners? Been thinking of that, and also adding a diffuser inside the top of the box--I can take one from a Chromega head for a 4x5 enlarger. Will also experiment with additional diffusion layer. Using only a piece from a flourenscent fixture at present. thanks, Bill |
#5
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help with light source for 8x10 enlarger
Bill wrote:
Hi, I'm building a new light source for an Elwood 8x10 enlarger. Have modeled the diffusion box on the one in my Saunder 4x5 machine. However, the illumination is not yet even: about 1 stop drop-off from center to edge. I've researched Fresnel lenses, and believe one would work (12x12 lens with a FL of about 250 mm, I calculate). The source I've found is in China, and the price is not reasonable. Questions: Will the Fresnel lens actually increase the edge brightness? Is the FL about right for this enlarge size? Background: The light source is two assemblies from Ektagaphic projectors, 250 W each, beaming into the difussion box through side holes to create a large bright spot at the top of the box. Because of the size of this spot, I believe the FL of the Fresnel lens shouldn't be critical. Thanks Bill, You might try giving Jeffry Kay a call at Lens and Repro in NYC a call. 212/ 675-1900 If he can supply parts he should be able to give you an idea of where to look. Feel free to use my name Dave Smith Yes, really, I have proof. =;~) Jeff is a friend and knows just about all there is to know about large format. Best, Dave |
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