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help with light source for 8x10 enlarger



 
 
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  #1  
Old April 9th 09, 03:18 PM posted to rec.photo.equipment.large-format
Bill[_12_]
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Posts: 3
Default 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  
Old April 9th 09, 04:48 PM posted to rec.photo.equipment.large-format
John J
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Posts: 110
Default 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  
Old April 9th 09, 06:00 PM posted to rec.photo.equipment.large-format
erie patsellis
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Posts: 35
Default 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  
Old April 27th 09, 06:12 PM posted to rec.photo.equipment.large-format
Bill[_12_]
external usenet poster
 
Posts: 3
Default 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  
Old April 27th 09, 07:40 PM posted to rec.photo.equipment.large-format
Dave[_8_]
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Posts: 30
Default 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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