Some of you asked how fast the FAST Box One can test and if it´s possible to test 1/4000th of a second and even faster.
There are good news: from now on it is possible to test up to 1/8000th of a second (<0,000125 second)
The alignment of the light source and sensor has to be perfect to achieve this, but you still got the sensor feedback option to do so!
Please consider the mentioned words down below:
Reciprocity Breakdown at Extremely Short Exposure Durations
In photography, reciprocity failure—often referred to in technical contexts as the Schwarzschild effect—is typically associated with longer exposures. However, under certain conditions, it can also affect images taken at extremely fast shutter speeds, typically those shorter than 1/1000 of a second. In such cases, the film emulsion may not react efficiently to the brief influx of light, resulting in underexposed images despite seemingly correct metering.
This high-speed form of reciprocity failure is not commonly encountered, and as a result, it hasn’t been extensively researched or documented. Most film manufacturers do not offer detailed correction data for exposures in this ultra-short range, largely because newer films are engineered to maintain accuracy even under these demanding conditions. For example, Kodak and Ilford’s modern emulsions generally do not require any exposure adjustment at speeds as fast as 1/10,000 second. Kodak’s technical notes for T-MAX 100, however, recommend a modest increase of one-third of a stop at that speed.
By contrast, films that use older emulsion technologies—such as Fomapan 100—may show signs of reciprocity failure even at 1/1000 second. Although Foma states in its product information that compensation is unnecessary from 1 second down to 1/1000 second, the film’s poor reciprocity behavior at longer exposures suggests that some degree of adjustment might become necessary at faster shutter speeds. Since the manufacturer provides no specifics for this range, photographers are left to determine appropriate corrections through trial and error with their own setups.