Enlarger lamphouse or bellows leak

Owned by Break/Fix — the room that fogs and the light that is not even, which names this entry as carrying the full signature and supplies the single observation that identifies the fault: a clean white border under the easel blades with a veiled picture area, because the blades masked that strip from light arriving down the lens path and from nothing else. Its second discriminator is the one this entry states from the other side — a lens-path fog grows with the exposure time rather than with the handling time. The capped-lens test belongs to commissioning the enlarger. This entry was built earlier on Kodak’s K-4 and on the geometry the course already taught.

What you see

Fog that is present only when the enlarger has been on, and strongest on the part of the paper nearest the column or nearest whatever part of the head is leaking. A test strip made with the lamp on for a long total time is worse than one made quickly, even at the same total image exposure.

The distinguishing feature against a room leak is that this one is switched: it appears and disappears with the enlarger, not with the door or the time of day. The distinguishing feature against safelight fog is the same thing from the other side — switch the safelight off and the fault survives.

Likely causes

1. An unbaffled vent in the lamphouse. A head has to lose heat, and a hole that lets heat out lets light out.
2. A pinhole or a split in the bellows, which on an old enlarger is the single commonest answer.
3. A negative carrier that does not mask the whole aperture, so light passes beside the negative rather than through it — which fogs the print and flares the image at the same time.
4. Gaps around a filter drawer or a condenser mount, opened by handling.

What is happening: the chemistry and physics

Two different things are happening and they look alike on the print, which is why the entry names both.

Light leaving the head sideways falls on the easel and on the paper at whatever angle the geometry allows. It is ordinary fog with a direction, and it adds density where the paper faced the hole.

Light leaving the head through the lens without having been through the negative is a different animal: it is flare, it lands inside the image, and it lifts the shadows of the print — which are the highlights of the negative — while leaving the rest nearly alone. Part VI’s flare veil entry is the camera version of exactly this mechanism.

The two are separable because the first is worse the longer the lamp is on in total, and the second scales with the exposure itself.

!The confirming test: run the lamp with the lens capped

Cap the lens, put an unexposed sheet on the easel, and run the lamp for the length of a printing session. Process it.

• The sheet fogs: light is leaving the head by a route that does not pass through the lens. The leak is in the lamphouse, the bellows or a mount, and the fix is baffling.
• The sheet is clean but prints still show lifted blacks: the light is coming through the lens, and the causes are a carrier that does not mask, a dirty or uncoated lens, or reflective surfaces around the easel.

Then find it in the dark. With the room dark and your eyes adapted for five minutes, switch the enlarger on with the lens capped and look at the head from every side. A leak that fogs paper is a leak you can see once your eyes are ready, and Kodak’s five-minute rule applies here exactly as it does to the room.

Diagnostic questions

• Does the fault track the lamp or the clock? Lamp means the head; clock means the room.
• Is the paper worse nearest the column? Bearing again, and it points straight at the leaking face.
• Does the carrier mask the whole negative aperture? Hold a piece of paper at the lens and look for light outside the projected frame.
• Has the bellows been extended fully? A split often only opens at full extension, so the fault appears at big enlargements and not at small ones.
• Are the easel and the walls near it dark? A white wall beside an easel returns some of everything the head emits.

Corrective action

Baffle rather than block. A lamphouse vent exists to keep the head cool; closing it trades a fog fault for a heat fault. A light trap — two offset baffles with a black interior — passes air and not light.

Patch a bellows from the inside with matt black material, and re-test at full extension.

Mask the carrier so that no light passes beside the negative, which improves the image as well as the fog.

Then repeat the capped-lens test, because this is a fault that is easy to half-fix.

Prevention

Keep the area around the easel dark, on the same principle that makes matt black paint a calibration operation inside a densitometer.

Inspect the bellows in the dark once a year, with the lamp on and the lens capped. It takes a minute and it catches a split before it costs a session.

Do not diagnose this with a coin test alone. Kodak’s warning stands: excessive fogging may show up only in the image area, because that area receives the enlarger’s light as well.