Investigations in array sizing 3. The center distance finding technique

Certification of NIST SRM 1962 - 3 micrometer diameter polystyrene spheres

“…Focal-spot patterns from the contacting microsphere structures were photographed on Type 57 positive film. This high-speed material (3000 ASA) has adequate dimensional stability [ 1 ] and low granularity, permitting its use for this SRM calibration. Seventy-six photographs were measured, containing over 4600 measured focal spots.…”

“…Therefore the measured diameter values in Table 1 are corrected afterwards by a somewhat arbitrary increase of 0.002 μm, and a systematic error 0.002 μm is entered in the Error Analysis. If a microsphere is elongated perpendicular to the line of sight, its focal spot will be elongated by the same amount [ 1 ]. The photographed focal spots are almost all very uniform and circular, with a diameter of 0.4–0.5 mm in the film plane corrersponding to 0.5 μm in the object plane.…”

Microscopy and Image Analysis

“…7.2.1.5). For monodisperse samples containing spherical particles, which can be arranged in linear rows of touching particles, size measurement can be conducted for a row of particles instead of single particles; this will increase precision [13,14]. The projected area and the related equivalent size of particles can be determined through visual comparison of the projected area with circles, squares or rectangles of different sizes or through digital image analysis.…”

“…A special way of sample preparation exists for monosized, spherical particles, in order to place them in a hexagonal arrangement with long, linear rows of touching particles [13,14]. The advantage of such rows is that the length of a row can be measured instead of that of single particles (a correction for particle compression may be necessary).…”

“…7.4). NIST has applied this method for certification of some of their Standard Reference Materials [13,14].…”