REGISTER

If you have misregister problems, it is often due to more than one factor For example, a 2mm spread can cancel a 2mm shrinkage so that the spread fits but an emulsion-to-emulsion contact shows shrinkage. It is important to follow a logical process of elimination to find the causes.

When an emulsion-to-emulsion contact does not fit, examine the vacuum frame very carefully. Turn the original and the contact film by 90 degrees and make a second exposure. Remember that any spread is larger than the original due to the geometry of the light; adding a diffuser at the film plane helps keep this to a minimum.

Fit problems are generally worse on very dry days because differences between films are exaggerated at low relative humidity. If using a light table to check any possible dimensional changes of the film, it should not have lamps which generate heat which will cause the film to expand. Films should not be left lying on light tables for long periods of time as most are usually warmer than the room temperature. The sheet of film nearest the glass will increase in size more than other films in the stack.

CONTACT FRAME

There are several types of light source which may be used in the contact frame and matenals must be matched to the light.  A tungsten halogen lamp provides a point light source and is for use in the darkroom. under red safelight conditions, with orthochromatic film: metal halide or xenon lamps are for use in ordinary light with daylight materials.

Where possible, ensure that the film is positioned centrally in relation to the position of the light source; this is particularly important when using a point light source For instance, if you normally contact 40 x50 cm work on a 76 x100 cm frame, the light should be centred over the area in which you normally place the 40 x 50 cm film. Do not use asingle point light source with multi-layer flats, as they will not be printed in register.

Lamp output will diminish with age and if exposures need to be lengthened this may be the cause. Check lamps at regular Intervals by exposing atest wedge on to the contact film using standard exposure and processing conditions A change in the number of steps visible on the contacted wedge indicates achange in lamp intensity. An easy way to check for exposure Uniformity is to expose a 50 per cent tint and read the result with a densitometer.

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