Curious enlarger problem that has me stuck

[Erik Ryberg]

I hope somebody can help me here. I have a very old 4x5 enlarger I have happily used for some time now though it is sort of junky, a "De Jure." It is a conden ser enlarger. I have been using a 135 mm lens for my 4x5 negatives with no prob lems. But recently I acquired an 80 mm lens (Schneider Companon-S) so that I may enlar ge 6x6 negatives with more ease. Only trouble is, the damn thing casts a tiny i mage - too small for the negative. There is massive light fall-off on the edges . So I lent the lens to my father who has a 6x6 enlarger and he used it on his enlarger with no trouble. But I can't get it to work on mine. Is there something about my enlarger that prevents me from using this lens? Sho uldn't a 4x5 enlarger/condenser head work fine with all formats smaller than 4x5 ? It is not vignetting on something internal. Any suggestions would be very we lcome. Thanks Erik Ryberg

[Richard Fish]

Ask you dad if he changed the distance between the condenser and the negative when he put on your lens, because that is what I think your problem is. For example, Omega has different condenser sets for different negative sizes; Beselers have the ability to change the distance between the negative and condenser, via a top bellows. You need to study the difference between your dad's enlarger and your's, and I think you'll solve your puzzle. Best wishes.

[Tony Brent]

The comments about the condensers are right. The condensers cast a cone of light down to the enlarging lens when it is in focus for making a print. If you chang e to a different enlarging lens like you did, it will be in a different portion of the cone of light from the condensers, and wont have full illumination. Thus the different lens mounts for the Omega and the adjustable condensers on the Bes elers.

There might be some locating rings or other markings inside your condenser housi ng for making these changes.

[james mickelson]

I have two De Jur enlargers and the small one I use for 35mm - 6x6 and the other one for 4x5. The 4x5 will not do anything else with out the light falloff. The smaller one will do up th 6x7. They are good enlargers as long as you have adjustments for back to front leveling. I understand from my dad that you could get different condenser lens containers for different formats. You could probably make them just as easily.

[Alan Gibson]

Yes, it sounds like a condeser problem. For even illumination, assuming a point light source, the image of the lamp, through the condensers, should fall on the lens. Because the 80mm lens is closer to the negative than was the 135mm, the condition no longer holds.

Possible solutions/kludges are:

- Obtain a shorter focal-length condenser.

- Stay with the 135mm lens.

- Increase the distance between the lamp and the condenser.

- Turn the point light source into a diffuse source, for example by putting tracing film between the lamp and the condenser. Beware of excessive heat.

[Erik Ryberg]

Thanks everybody,

I clearly needed a lesson in the physics/optics of condensers, and got one. For now I'm going to stick with the 135 mm lens but have my eye out for some opal glass to try. Meanwhile my dad got a nice 80 mm lens for free. . . .

Erik Ryberg