Components
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Main body, clip and suction cup
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These components are fully standardised and produced using injection moulding techniques. Filters are inserted manually during construction and tested to provide the correct alignment of polarising filters. The clip is suitable for phone bodies up to approx 7 mm depth. The suction cup prevents the unit from sliding off and helps to hold iSPEX in place when mounted in front of the phone camera. Prior to mounting iSPEX on a phone, ensure that the lens of the camera and the phone body are clean to provide good quality measurements. 

Positioners
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Positioners are parameterised by the location of the horizontal and vertical end-stops which, seen when looking at the phone screen, align with the left and top of the phone body without custom case or sleeve.

For popular camera models, injection-moulded positioners may be available. These are produced in small batches and are very stable and sturdy, allowing the positioner to be clipped onto and removed from the iSPEX main body multiple times. 

Alternatively, 3D printing provides flexibility to improve the way iSPEX is seated onto the camera frame. Positioners are then printed with the part clipping into the main body on top, and filler structure to hold up the body during printing. Printing is done at 0.1 mm layer depth or finer, resulting in a clip mechanism which should allow for a few removals over time. However, it is recommended that, **after testing** the correct positioning, the main body and positioner are bonded with superglue. 

To design a new positioner, measure the distance from the phone body edge to the main camera (i.e. 1x zoom rather than wide-angle or zoom camera in multi-camera phones). Additionally, a cutout in the horizontal end-stop can be parameterised for phones with buttons along the side. To improve how iSPEX 2 is seated on phones with protruding cameras, a further frame around the camera island can be configured in 3D printed versions.


Grey cards
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A photographer grey cards is standardised to provide 18% spectrall neutral reflectance. To characterise differences across manufacturers we look at the reflectance spectrum measured at the reflectance port of an integrating sphere.