Point source enlargers. Refocusing condensers and lamp question.

[Ulrix]

Care to share the titles of the books you found useful?

Sure. Awating delivery …

 

[Ulrix]

Sure. Awating delivery …

So far, the only one I’ve found useful and informative is Hans Namuth’s description of using a point light source enlarger. You can find it in Darkroom 2, Jain Kelly, Lustrum Press 1978.

Available here:

Darkroom 2 : Free Download, Borrow, and Streaming : Internet Archive

160 p. (p. 160 blank) : 29 cm

archive.org

 

[Ulrix]

I learned this the hard way ... the Durst Varipoint Enlarger fitted with a point light source, will need T coated condensers and T coated glass in the negative carrier. It will not work properly using the regular AN glass and Femacon condensers. These condensers are made for the more common opal light bulb.

 

[koraks]

What happens if you use the non-T coated condensers? Just curious since I have in mind to try something similar one of these days on my 138, but all I have is the regular condensers.

 

[Ulrix]

Here's ns a picture of the projection on the base board without negative. I suspect internal reflections gives the rings and centered hot spot. With the T marked condensers, the illumination is even. This is the Varipoint 1200. 138 may be differnt-

 

[koraks]

Ah; thanks so much, yes, that makes sense. I've boosted contrast in the pic so as to emphasize the issue:

I assume that no amount of trying to optimize distances or the condenser configuration for the particular lens used improved the issue?

 

[choiliefan]

Is this the type of machine you are using?
He shows the condensers for instance but the tutorial is in French.

 

[Ulrix]

Ah; thanks so much, yes, that makes sense. I've boosted contrast in the pic so as to emphasize the issue:
View attachment 391870
I assume that no amount of trying to optimize distances or the condenser configuration for the particular lens used improved the issue?

there is no adjustment to the bulb that makes the rings disappear. Swapping the condenser to a T coated and voila! Gone.

 

[Ulrix]

Is this the type of machine you are using?
He shows the condensers for instance but the tutorial is in French.

Exactly. That’s the one, and he has the coated glass.

 

[Paul Howell]

Wonder why my old federal 2 condenser 6X9 seemed to work fine without coated condensers? No ring at all, all I did was paint the lamp housing with high temp flat black, had a light shop replace the bulb with a halogen bear bulb and dimmer. I was able to move the lamp up and down but not side to side. I used an Kodak Ektara 50 and 90mm 4 element lens, I think they were coated.

 

[Ulrix]

Wonder why my old federal 2 condenser 6X9 seemed to work fine without coated condensers? No ring at all, all I did was paint the lamp housing with high temp flat black, had a light shop replace the bulb with a halogen bear bulb and dimmer. I was able to move the lamp up and down but not side to side. I used an Kodak Ektara 50 and 90mm 4 element lens, I think they were coated.

It looks like a diffraction pattern … but I would expect it’s due to internal reflections. If the filament size is bigger, the pattern also disappears. The Varipoint projects a pin head sized light source from the Pulamp bulb.

 

[avandesande]

I have perfectly even light circle with the standard D2 4 1/2 condenser. The nodal point changes depending on the size of the print, for a 5x7 print I use a 135mm lens and for 11x14 use a 105mm.

 

[Paul Howell]

It looks like a diffraction pattern … but I would expect it’s due to internal reflections. If the filament size is bigger, the pattern also disappears. The Varipoint projects a pin head sized light source from the Pulamp bulb.

Must be the halogen bulb, not pin head size, smaller than the filaments in a standard clear tungsten bulb much larger than pin head size. I never seen either the point source for the Omega D or Bessler 4X5, in AA book the bring there is a picture of the point source sitting on a shelf his 4X5 motor Bessler.