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srinivas
2-Apr-2006, 02:12
what is the international standard for calibration of step wedge film, I received one step wedge, manufatureer calibrated in nov 2003 but my first started on 18/03/2006 , how long i can use this step wedge
Conrad Hoffman
2-Apr-2006, 07:28
No idea what standards there are, if any exist. Usually calibration intervals for anything are established by need and history. X-Rite would like you to buy new calibration films every year, but IMO that's way too often. I have step wedges from 30 years ago that haven't changed by any amount I can measure. Stored properly, why should they? If we were dealing with electronic equipment where measurements in the parts-per-million region matter, it would be one thing, but photographic density measurements aren't all that precise to begin with, comparatively speaking. Calibrate at an interval that suits your needs. Note that the interval may be shorter for color standards.
Terence Spross
2-Apr-2006, 07:35
The manufacturer will have traceability from certified photometry instruments to a national standards lab (such as the NIST in the US) and used to measure (calibrate) the wedge just after it was made. The certification will have tolerances abd the manufacturer should have information on fading or other changes that can occur to the step wedge due to exposure to light in use or storage and other changes. There should be a prediction based on that when the wedge could go out of tolerance. There should also be info on what mishandling could void the calibration, such as heat above a certain temperature.

A standards company can re-certify the wedge, if necessary. It is a good idea to have at least one other standard in your possession to check against. For example a calibrated illumination source that was measured with a photometer through a step on the wedge and rechecked periodically and compared with your densitometer reading.

In my opinion, if you have another step wedge, you should store one in ideal conditions and use the other for regular periodic use. Then evey few months do a comparison.