Versalab Parallel: Parallel Accuracy

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PARALLEL ACCURACY

The absolute accuracy of the PARALLEL is well beyond normal photographic printing or copying requirements. The completed enlarger alignment accuracy will be limited by capability inherent in the specific enlarger alignment mechanisms and the patience of the person performing the alignment. There is usually no need to try and align to the limit of the accuracy level of the PARALLEL, but it may pay off on large critical enlargements.

The PARALLEL can indicate an out of parallel condition of as little as .0006" across a 35mm. negative, which is less than 1/6th the thickness of most negatives.

In this note we will use inches to describe the parallelism error since it is more adapted to this measurement than degrees. In some cases the error will be stated in a certain amount of error per inch of width. This can be converted to a specific negative by multiplying the error by the number of inches of width of the negative.

One can determine the alignment error by a simple calculation based on the position of the reflected dot. The reflected error in parts of an inch, divided by 2, divided by the projection distance in inches = error in inches per inch (out of parallel))

As an example, if the dot is out of the hole by 1/16" of an inch and the distance between the reflector and the PARALLEL is 20" (top of the projector box to the negative stage for instance), then the negative stage is out of alignment by only about .0016" per inch or 1/3 of the thickness of the negative for each inch of width of the negative. That is just over the thickness of the negative (.008") error from one side to the other of a 4x5!

The greater the projection distance the easier it is to see alignment error since the displacement of the dot is proportional to the projection distance.

The PARALLEL is very usable up to 20 feet. The beam becomes less distinct but the error is so magnified by the projection distance that judging alignment remains easy. In some cases the room lights will need dimming in order to properly see the reflected dot.