Technical Support Document 039 - 5/97

POSSIBLE CAUSES OF NEGATIVE POPPING

Visual Symptom

1. Projected image is sharp around the edges and becomes increasingly unsharp towards the middle.
2. Usually associated with larger format negatives.

Visual Indication

1. Indications that the center of the negative is higher or lower in the middle.

Usual Causes

1. Negative insecure in the negative carrier.
2. Excessive heat coming from the color head.
3. Excessive negative curl.
4. Vacuum being created by the color head.
5. Bad projection lens.

Remedies

1. Negative Carrier

Normally unequal pressure being applied around the periphery of the negative will allow the negative to pop. Very often seen on carriers which are hinged at the rear and only the weight of the enlarger head ensures the security of the negative.

2. Excessive Heat

This normally ranks very high on the list. The heat causes the negative to expand. Differential expansion between the emulsion layer and base causes the negative to pop downwards. This can be aggravated if the negative is held in the carrier very securely. i.e. it can only pop to relieve the stress.

3. Excessive Negative Curl

Normally associated with drying films in negative drying cabinets. There is a mistaken belief that film dries more quickly if the drying air is made hotter. This is a false premise. It is the passage of large amounts of dry air moving across the surface of the film which causes it to dry.

4. Vacuum

A gap between the light box and negative carrier sometimes allows a vacuum to form across the negative. The effect is to suck the negative upwards.

5. Bad Projection Lens

Unsharpness caused as a lens aperture is stopped down. Observed to be worse in the middle of the projected area.

Conclusion

On the assumption all the normal remedies have been tried I suggest first:

1. Check the security of the light box in the color head, possibly change it.

2. Exchange all the negative carriers, except the glass 4" x 5".

3. Exchange the Starlite.