Uneven light 6x6 enlarging

[Michael W]

This problem has me stumped, details as follows.
LPL 7700 condenser enlarger
6x6 B&W neg printed onto 8x10 paper

enlarger set up as per instructions:
light bulb pushed to inner position
top condenser removed
80 mm lens with reversed lens mount (i.e. 50mm lens goes in concave, 80mm goes in other way round)

The problem is that one side prints unevenly, lighter than the rest. Please note it is not the corners but most of one side - the edge nearest to where we are standing to use the enlarger.

The problem is not on the film - it was a well exposed & processed neg of a vase of flowers against a white wall. Wall tonality was quite even on the neg & this is what makes it so obvious when one edge prints lighter.

I have seen something like this happen before when using small filters in the filter tray with a cardboard frame to hold the filter, i.e. the frame blocks some light. In this case we had a full size filter in the tray. But the problem looks similar to that, i.e. that something is blocking the light at one edge. For the life of me I can't see what it could be, wondering if this is something anyone else has experienced & overcome.

 

[Michael W]

A couple more things I thought to mention
It was a Nikkor 80mm lens
aperture was closed down 2 stops.

I'm thinking to try closing the aperture down further.
Or try a 105 mm lens.

 

[jerry lebens]

It could be something to do with having a wrong condenser set up, I'm not familiar with the condenser options on LPL.

Or the bulb is somehow displaced (unlikely).

If the obscured section has a straight edge then, most likely, is that one of the baffles on the neg carrier is, inadvertently, obscuring the light path : on an LPL they're controlled by two (usually yellow) tabs on the front of the neg carrier, make sure they're pushed off to their respective sides, right out of the light path (there are two horizontal/vertical baffles, too, controlled at the LHS of the carrier).

It's easy to knock them into the light path with a sleeve etc, in over 30 years darkroom experience I've never actually found much use for them....

Otherwise, if it's not that, screw the lens off the enlarger and stick your head underneath with it switched on, you should be able to see the problem quite easily. Just make sure the head is locked in place!

Regards
Jerry

 

[Rick A]

Is the bulb centered in the lamp housing? That is the only thing I can envision as a probable cause.

 

[brucemuir]

Is the bulb centered in the lamp housing? That is the only thing I can envision as a probable cause.

Ditto.
My Omega DII would print 135 and up to 6x9...no problem.

When I started to do 4x5 I was getting funky coverage. Turned out the bulb was not positioned correctly in the lamp housing.

It was only slightly askew but that was enough.

 

[Michael W]

If the obscured section has a straight edge then, most likely, is that one of the baffles on the neg carrier is, inadvertently, obscuring the light path : on an LPL they're controlled by two (usually yellow) tabs on the front of the neg carrier, make sure they're pushed off to their respective sides, right out of the light path (there are two horizontal/vertical baffles, too, controlled at the LHS of the carrier).

We tried two neg carriers; first a glassless one that was 6x6 size. This is when the problem was first apparent. Changed to one of the ones you mentioned, a glass carrier with blades however they were out of the way & I'm confident not the cause.
I'm thinking to have a closer look at the position of the condensers, they were in the correct slots but I will look to see if they were misaligned somehow.
The lamp is something else to check.
I might also be able to test a LPL colour head which could be interesting as it won't have the condensers.

 

[Andrew K]

I use a 7700, and have even lighting with it. I would check the following

1 - you have the right globe fitted. The original globe is a tear drop shaped gloge - if you use the wrong globe you will get uneven light

2 - the globe adjustment - make sure it is in the right place.

Also - when using a 80mm lens on a 7700 I use a flat lens board. However using the 50mm board in reverse won't cause any uneven lighting...

good luck